Resting spores are critical to the ability of many entomophthoralean fungi to initiate epizootics after periods of host scarcity, but the influence of environmental conditions on their activity is poorly understood. In this study, the effects of temperature and soil moisture on the activity of resting spores of Furia gastropachae (Raciborski) Filotas, Hajek, and Humber, an entomophthoralean pathogen of the forest tent caterpillar, Malacosoma disstria Hübner, were investigated in the laboratory. M. disstria larvae were exposed to soil containing F. gastropachae resting spores under nine moisture-by-temperature treatments designed to approximate the range of ambient abiotic conditions present during the early spring period when host and pathogen are active. Both infection and spore production were maximized at high moisture levels approaching saturation but inhibited in highly saturated soils. The percentage of M. disstria larvae dying from F. gastropachae infections was maximized at cooler temperatures, as was the production of conidia from cadavers. This may be related to host phenology; F. gastropachae maximizes infection and dispersal at the cooler temperatures occurring when its host is active. In this study, a Percoll-based technique for the quantification of entomophthoralean resting spores in soil was applied to determine that resting spore densities exceeded 500/g dry soil, 4 yr after an F. gastropachae epizootic had been observed.

The predation rate per hour of Macrolophus pygmaeus Rambur (Hemiptera: Miridae) under light and dark phase was examined in relation to the host plant, photoperiod, temperature, and life stage of the predator. Individuals from each nymphal stage plus adults of both sexes of M. pygmaeus were put individually into petri dishes on an eggplant or pepper plant leaf infested with nymphs of Myzus persicae (Sulzer) (Homoptera: Aphididae). The experiments were conducted at three photoperiods (8:16, 12:12, and 16:8 h [L:D]) and temperatures (20, 25, and 30°C) on eggplant and pepper plants. Generally, the predation rate was significantly higher in the dark than in the light phase, particularly in the case of larger instars and adults. Interactions between factors showed that the preference of this predator to feed at night is much higher on pepper plants than on eggplant, and this difference is more prominent at 30°C. The importance of these results in understanding foraging behavior and how aspects of this behavior affect the predator’s potential in biological control are discussed.

Protist communities found in the hindgut of subterranean termites (Rhinotermitidae) historically have been quantified and identified using a variety of methods, thus making comparisons between studies difficult. We examined four saline solutions and compared protist estimates by using two different cell-counting platforms. Estimates of protist populations were greater using a hemocytometer counting chamber than sealed coverslip mounts. Estimates of the protist population per Reticulitermes flavipes (Kollar) worker averaged 90,000 in Trager U, 79,000 in Ritter, 68,000 in Mannesmann, and 50,000 in 0.6% NaCl saline solutions. The percentage of protist survivorship significantly decreased after 5 min under microscopic examination in untreated media. Sparging one of the saline solutions (Trager U) with nitrogen gas provided a solution where protist populations averaged 91,000 and percentage of protist survivorship did not significantly decrease for 15 min. Identification and quantification of protists require time, and extending cell life provides more time to make accurate counts. We therefore propose the technique described in this study be adopted for its ease of use and improved accuracy.

Laboratory studies were conducted to determine the effects of incorporating selected almond fungicides into the diet of larval honey bees, Apis mellifera Linnaeus. One-day-old larvae, from mixed Italian stocks, were grafted to basic larval diet or basic diet containing various fungicides. Experimental concentrations were calculated from field dose application rates of formulated product per hectare. Larvae were transferred to fresh diet daily and incubated in the dark at 35°C and 95% RH. After defecation, prepupae were moved into a dark incubator at 35°C and 75% RH. Mortalities of larvae, prepupae, and pupae were recorded daily. No larvae fed Captan, Rovral, or Ziram completed development to adults. In the case of Rovral, a novel amorphogenic effect was observed. There were no significant differences in total mortality between the controls and larvae fed Abound, Elevate, Flint, Rally, and Vangard.

Dispersal of adult tortricid moths between habitats may have important consequences for pest management in orchards, but little is known about how flight parameters are affected by environmental conditions during preimaginal development. The influence of changing temperature and photoperiod (both singly and in combination) as well as of larval crowding and food deprivation were investigated in Cydia molesta Busck (Lepidoptera: Tortricidae), a species that has been found to disperse after peach harvest and colonize pome fruit orchards. Comparative assessments of flight parameters were made on a computer-linked flight mill and life history traits were evaluated. A significant increase in flight performance was correlated with preimaginal exposure to decreasing photoperiod. In addition, pupal development was delayed and larger individuals emerged, but preimaginal survivorship was reduced. Decreasing and increasing temperature regimens and increasing photoperiod did not influence adult flight. Larval crowding was associated with increased flight, but the differences were not statistically significant. Food deprivation was associated with accelerated preimaginal development, lower pupal weight, less fecund adults, and reduced flight. We propose that the main factor eliciting dispersal in this tortricid is decreasing photoperiod.

Bruchidius dorsalis Fahraeus (Coleoptera: Bruchidae) enters winter diapause in either the fourth (final) instar or during the adult stage (Kurota and Shimada 2001, 2003b). In the middle part of Japan, it overwinters in several developmental stages: nondiapausing young instars, diapausing instars, and adults (Kurota and Shimada 2002). To understand the relationship between the complex overwintering stages and the adaptive diapause strategy of B. dorsalis, I investigated (1) overwintering survivorship in developmental stages observed in the field and (2) cold hardiness at all stages including nonoverwintering ones such as eggs and pupae after enduring a controlled chilling experiment at 5°C for 100 d. The following results were obtained: (1) survivorship of nondiapausing larvae under natural conditions was almost as high as that of diapausing larvae and adults, and (2) cold hardiness in eggs and pupae was much lower than the other developmental stages in terms of survivorship and reproductive ability after the chilling treatment. From these results, I concluded that larval and adult diapause of this species would be induced at the most appropriate time to avoid overwintering in developmental stages with low cold hardiness. The complex overwintering stages in species that inhabit the middle part of Japan are likely to result from the adaptive timing of diapause induction at the two stages.

We investigated the performance of larvae of the invasive maize, Zea mays L., pest Diabrotica virgifera virgifera LeConte (western corn rootworm) on roots of alternative host plants. During laboratory feeding trials, we measured growth and amount of ingested food and determined the food conversion efficiency of second instars. We tested eight species of weeds (seven monocots and one dicot) and three monocot crops with regard to host plant suitability by using a newly established method. We additionally examined the carbon/nitrogen ratio and the phytosterol content of the different plant species as parameters to interpret larval performance. Larval growth, the amount of ingested food, and the food conversion efficiency differed significantly between plant species. Plant species with a high nitrogen content were less suitable for D. v. virgifera development. The phytosterol content had a significant influence on the amount of ingested food, but not on larval weight gain. The performance of D. v. virgifera larvae on alternative hosts was comparable with their performance on maize. The ability to use alternative hosts for larval development may contribute to the invasion potential of D. v. virgifera and has important implications for integrated pest management.

A laboratory experiment compared development and kikuyu, Pennisetum clandestinum Hochst. ex Chiov. South, consumption in preimaginal grass webworm, Herpetogramma licarsisalis (Walker), at 15, 18, 20, and 25°C. Mean developmental time from oviposition to adult emergence was 25.0 d at 25°C, 43.4 d at 20°C, 50.4 d at 18°C, and 81.4 d at 15°C. Survival decreased with decreasing temperature but not significantly. Total and daily kikuyu leaf area consumed per larva differed significantly with temperature. Leaf consumption increased exponentially with instar. Some larvae developed through six instars, rather than the usually reported five, at temperatures <25°C. Compared with five-instar H. licarsisalis, those with six instars spent longer in the egg stage, had smaller head capsule widths at all but first instar, faster developmental rates but lower kikuyu consumption for each stadium above the second, and slower egg-adult development. Developmental time from egg to adult emergence was significantly shorter for females than for males due to a shorter female pupal stage. Results from this experiment support the view that H. licarsisalis is surviving close to its lower developmental limits over the winter period in Northland, New Zealand, and provide data that will be useful in conjunction with field-collected data for predicting potential geographical distribution and survival.

The development, reproduction, and life history of Encarsia citrina Craw were studied in the laboratory on San Jose scale, Quadraspidiotus perniciosus (Comstock), at constant temperatures of 15, 17.5, 20, 25, 27.5, and 30°C at 60–70% RH, and a photoperiod of 16:8 (L:D) h. Larval development did not occur at 15 and 30°C. Total developmental time varied from 22.7 d at 27.5°C to 47.4 d at 17.5°C. The lower development thresholds for larval, pupal, and egg to adult periods were 10.4, 6.3, and 9.0°C, respectively. The number of degree-days required to complete development was 434.8. The average longevity of adults ranged from 34.3 d at 15°C to 8.0 d at 30°C. The average fecundity of females ranged from 96.3 eggs at 20°C to 40 eggs at 17.5°C. Life table parameters were also determined at four constant temperatures (17.5–27.5°C). The intrinsic rate of increase, r_m, values for E. citrina ranged from 0.074 at 17.5°C to 0.176 at 27.5°C. The highest net reproductive rate, R₀, of 93.7 female offspring/female was estimated at 20°C. The mean generation time, T, ranged from 49.3 d at 17.5°C to 23.4 d at 27.5°C. The results of this study emphasize E. citrina survival and population growth under varied temperature conditions.

Morphological variations in insects have been shown to be influenced by latitude and elevation. Here we show that these two parameters markedly influence the appearance of the corn leafhopper Dalbulus maidis (DeLong and Wolcott). Leafhopper samples were collected in maize from 27 localities in 10 Brazilian states, with latitudes from 5 to 28° S and elevations from 16 to 1,628 m. D. maidis was the only Dalbulus species found in the samples. Up to 10 males and 10 females of D. maidis from each collection site were evaluated for size, pigmentation, and body weight. Females were always bigger and heavier than the males in the same locality. For both sexes, there was a positive and significant correlation between the morphological variables measured and the latitude and elevation from where specimens were collected. Individuals from higher latitudes (southern region) were bigger, darker, and heavier than those from lower latitudes (northeastern region). There was also a tendency for an increase in body weight, head capsule width, and wing length at higher elevations.

Life table analysis was performed on Podisus maculiventris (Say) adult females at constant temperatures of 16, 26, 30, and 36°C. Survivorship curves were linear type II, with steeper rates of decline at higher temperatures. Longevity at 16°C (47.2 d) was significantly longer than that at 26°C (14.3 d) or 30°C (12 d). Adults under the 36°C survived only 4.9 d and laid no eggs. Percentage of eggs that hatched was relatively constant at ≈ or about 40% at 16, 26, and 30°C. Numbers of egg clutches (ranging from 5.9 to 9.4), eggs per clutch (13.6–14.6), and eggs in the first clutch (9.0–15.1) did not differ significantly at these three temperatures. However, preoviposition period was significantly longer at 16°C (20.3 d) than at 26°C (6.3 d) and 30°C (4.9 d). Number of eggs laid was related to body weight by the equation E = −139.1 3.49w, where E is number of eggs laid per female lifetime, and w is the weight of the predator female. Life table analysis of P. maculiventris female adults showed that both net reproductive rate (R₀) and gross reproductive rate (GRR) were highest at 26°C, estimated at 47.8 and 156.0 females per female, respectively. However, the shorter generation times at 30°C (T = 42.2 d) resulted in higher values for the intrinsic rate of increase (r = 0.09), the finite rate of increase (λ = 1.09), and doubling time (DT = 7.7 d). Analysis of cumulative egg production suggests that 26°C may be more suitable for maintaining colonies of P. maculiventris because of the sustained levels of egg production over a longer period, compared with the 30°C treatment.

The attractiveness of Barley yellow dwarf luteovirus (BYDV)–infected wheat plants to Rhopalosiphum padi L. was evaluated under laboratory conditions. Two untransformed wheat varieties, virus-susceptible Lambert and virus-tolerant Caldwell, and one transgenic wheat genotype (103.1J) derived from Lambert and expressing the BYDV coat protein gene, were tested in three bioassays. First, R. padi responses to BYDV-infected or noninfected Lambert and Caldwell were evaluated. Significantly more aphids settled onto virus-infected than noninfected plants when aphids were able to contact the leaves. Second, aphid responses to headspace from virus-infected or noninfected Lambert and Caldwell were tested. Significantly more aphids congregated on screens above headspace of BYDV-infected plants than above headspace of noninfected plants of both varieties. Third, aphid responses to headspace from virus-infected or noninfected and sham-inoculated (exposed to nonviruliferous aphids) Lambert and 103.1J plants were examined. Significantly more aphids congregated on screens above BYDV-infected than above noninfected or sham-inoculated Lambert. No significant differences in R. padi preferences for headspace above BYDV-infected compared with noninfected or sham-inoculated 103.1J plants were observed. The concentration of volatiles extractable from whole plant headspace was greater on BYDV-infected Lambert than on BYDV-infected 103.1J, noninfected, or sham-inoculated plants of either genotype. This is the first report of volatile cues associated with BYDV infection in wheat plants influencing the behavior of the vector R. padi. Additionally, these findings show for the first time that transgenic virus resistance in wheat can indirectly influence the production of volatiles making virus-infected plants less attractive or arrestant to aphids than are infected untransformed plants.

A laboratory bioassay was developed for testing oviposition preference of southern green stink bug, Nezara viridula (L.) (Heteroptera: Pentatomidae), toward chemicals extracted from soybean, Glycine max (L.) Merrill, pods and leaves. In this bioassay, an artificial substrate (cheesecloth) was stretched over a wooden ring (embroidery hoops), treated with plant extracts or chromatographic fractions, and then exposed to adult stink bugs to assess oviposition preference. The methanol extract of pods stimulated the greatest oviposition. After a chromatographic separation on a reverse phase open column, the most active fraction derived from this extract was that eluted with 20% methanol in water. After subjecting this fraction to chromatography on silica, the greatest activity occurred in the fraction eluted with 60% methanol in methylene chloride. Further fractionation of this material by thin layer chromatography gave no single fraction with demonstrated activity, but the recombined fractions were again active, indicating that multiple components are probably involved in eliciting oviposition. Antennectomized females did not differentiate treated versus untreated substrates, but females with the hairs of the genitalia coated did, indicating that the oviposition-eliciting compounds were sensed by the antennae, rather than by hairs of the genital plaques.

Spatial and temporal variation in the genetic structure of local populations of tobacco budworm Heliothis virescens (F.) were surveyed using 11 polymorphic allozyme and 36 random amplified polymorphic DNA (RAPD)-polymerase chain reaction markers. Allelic and genotypic frequencies were calculated from male moths caught in pheromone traps from 5 to 6 local populations from 1995 to 1997. Overall, populations showed little spatial differentiation that indicates a high effective gene flow rate over the spatial scale under investigation. The data show that allelic differentiation arose more frequently in the second generation than in any other generation, suggesting that dispersal was more limited during this period of the summer. Based on allozyme data, estimates of Wright’s standardized genetic variance among populations, F_ST, ranged from 0.001 to 0.018, with the highest values found from the second generation. Estimates based on bootstrapping over loci suggested that genetic variance among populations was significantly higher in the second generation than other generations. Genetic variance tended to increase progressively through the season, peaking in the second generation and decreasing in the latter part of the summer. This temporal pattern of genetic structure is concomitant with changes in gene flow rates and may be influenced by phenological changes in the primary host plants. The F_ST estimates and average heterozygosity from RAPD markers were consistently higher than those estimated from allozyme markers. However, patterns of change over the course of the summer were similar, and the two types of genetic markers provide similar insights into the dispersal biology of H. virescens.

A seasonal development study of the cerambycid beetles Phoracantha recurva Newman and Phoracantha semipunctata (Fabricius) (Coleoptera: Cerambycidae) was conducted under field conditions to look for differences in the developmental parameters of these congeneric species in southern California. Neonate larvae were introduced into eucalyptus logs in February, May, July, and October, and the infested logs were held in field cages at two locations: an inland desert site and a more temperate coastal site. Development times from neonate larva to emerged adult and percent emergence were recorded for beetles from all log cohorts at both sites. Under southern California climatic conditions, P. semipunctata seems to complete only one generation per year. Adult P. semipunctata emerged from infested logs from June to October. In contrast, P. recurva seems to be able to complete one generation and begin a second generation within the same year. Adult P. recurva emerged from infested logs from February to October. Across all treatments, a greater percentage of P. recurva (70 ± 2.5%) completed development in host logs than P. semipunctata (64 ± 1.5%). The majority of P. recurva (74.9%) and P. semipunctata (99.4%) emerged during June, July, and August. Host quality was correlated with beetle size. Overall, the differences in the developmental parameters of the two species may be contributing to the replacement of P. semipunctata by P. recurva in their shared habitat niche in southern California.

The goals of this study were to determine the population dynamics of sweetpotato whitefly, Bemisia tabaci (Gennadius); green peach aphid, Myzus persicae (Sulzer); and the cotton/melon aphid, Aphis gossypii Glover, as well as to explore the incidence of the complex of aphid-borne viruses of watermelon, Citrullus lanatus L., on different planting dates. Four (1998–1999) and six (1999–2000) watermelon plots were monitored under grower management conditions in La Huerta and Casimiro Castillo, Mexico. Plant growth, sweetpotato whitefly, and aphid (adult and nymph) populations, and percentage of virus-infected plants were measured in fall–winter watermelon plots planted at different dates. The population of sweetpotato whitefly varied significantly by planting date and showed two different population patterns. Watermelon planted in early October had higher population density at young developmental stages, whereas plantings from mid-October had more adults at flowering or harvesting. Aphid species may be present at any time in fall–winter watermelon. However, higher levels of infected plants and more damage caused by viruses occurred when watermelon was planted on 16 November or later. Several factors acting separately or interactively may influence the population dynamics of vector populations and the complex of viruses in watermelon. Current levels of vector populations (nymphs) may not be high enough to produce direct damage to watermelon plants, but adults may be important factor in the viruses’ infection process. Planting before mid-November may aid in getting lower levels of infected plants and improving yield.

The high-altitude wind-borne migration of beet webworm, Loxostege sticticalis, moths with other insects and their short-distance dispersal were observed with a digital scanning radar and twin light-traps (a vertical-pointing searchlight trap operated alongside a ground-based conventional light-trap) in northern China in 2002. Catches in both light traps suggested there were four flight periods of L. sticticalis during our study. The ovarian development stage of females caught in the light traps coupled with radar observations indicated that L. sticticalis migrated to the northeast in early June, whereas locally bred moths dispersed over shorter distances in mid-July and early August. The variation of the area density of insects through time during the spring migration was different from that during the summer dispersal; there was no density peak during spring, but such a peak occurred every evening in summer. Collective orientation by the moths was observed in the spring migration, with the direction of orientation being toward the northeast. In contrast, there was no common orientation in summer. Multilevel layering of migrants was seen every night in our observations in both spring and summer. The layering phenomenon was related to wind speed maxima rather than to temperature inversions when the air temperature was above the threshold for migration.

Spatial distribution patterns of black-legged ticks, Ixodes scapularis, in deciduous and coniferous woodlands were studied by sampling ticks in different woodland types and at sites from which deer had been excluded and by quantifying movement patterns of tick host animals (mammals and birds) at the Lighthouse Tract, Fire Island, NY, from 1994 to 2000. Densities of nymphal ticks were greater in deciduous than coniferous woods in 3 of 7 yr. Only engorged ticks survived the winter, and overwintering survival of engorged larvae in experimental enclosures did not differ between deciduous and coniferous woods. Nymphs were not always most abundant in the same forest type as they had been as larvae, and the habitat shift between life stages differed in direction in different years. Therefore, forest type by itself did not account for tick distribution patterns. Nymphal densities were lower where deer had been excluded compared with areas with deer present for 3 yr after exclusion, suggesting that movement patterns of vertebrate hosts influenced tick distribution, but nymphal densities increased dramatically in one of the enclosures in the fourth year. Therefore, movements of ticks on animal hosts apparently contribute substantially to tick spatial distribution among woodland types, but the factor(s) that determine spatial distribution of nymphal I. scapularis shift from year to year.

American beech, Fagus grandifolia Ehrhart, is currently threatened by the insect-mediated disease complex known as beech bark disease. The organisms (beech scale, Cryptococcus fagisuga Lindinger, and two pathogenic fungi, Nectria galligena Bresadola and Nectria coccinea variety faginata Lohman, Watson, and Ayers) associated with beech bark disease were assessed using a qualitative rating system and correlated with other biotic and abiotic factors in 10 permanent plots in the Great Smoky Mountains National Park from spring 1994 through spring 1997. Tree mortality, as well as the presence of another scale species [Xylococculus betulae (Pergande)], also were documented and analyzed. During this study, incidence of C. fagisuga and overall tree mortality increased (55.6–87.9 and 16.0–26.8%, respectively). A forward stepwise logistic regression model selected average overall ratings of C. fagisuga, sum of presence of X. betulae, average presence of. X. betulae, average overall ratings of Nectria spp., maximum presence of X. betulae, sum of south ratings of C. fagisuga, average south ratings of C. fagisuga, and diameter at breast height (dbh) of the tree as significant variables that best explained mortality of American beech. Pearson correlation analysis showed significant associations between ratings of Nectria spp. and C. fagisuga from both the previous season and previous year during fall 1996 and spring 1997. Moderate correlations between elevation, as well as aspect, and north, south, and overall ratings of C. fagisuga from fall 1995 to spring 1997 were documented. The significant association between presence of C. fagisuga and infection by Nectria spp. suggests that control of C. fagisuga could decrease occurrence and slow the spread of beech bark disease. Unless appropriate control and/or management of the disease complex is identified and implemented, mortality of American beech is expected to increase throughout most areas in the Great Smoky Mountains.

Distributions of soil macroarthropods were studied monthly for 1 yr (February 2001 to January 2002) in three depth strata (0–8, 8–16, and 16–24 cm) at six sampling sites along a moisture gradient stretching from the shore of Lake Yale, central Florida, to an upland hammock. Annual mean density of total soil macroarthropods at these sites varied from 312 to 1,809 individuals/m²; highest density was recorded near the center of the gradient. The most abundant groups of soil arthropods were Isopoda, predominantly Armadillidium vulgare (Latreille), and Diptera larvae (mostly Limoniidae, Chironomidae and Bibionidae). Species of five genera of Chironomidae (Paraphaenocladius sp., Pseudosmittia sp., Metriocnemus sp., Bryophaenocladius sp., and Smittia sp.) were found. Total number of macroarthropod species at individual sites varied between 40 and 70. The majority (61–92%) of soil macroarthropods from all sites was recovered from the near-surface stratum. Proportion of soil macroarthropods found in the two deeper strata increased with distance from the shoreline, elevation above lake water level, soil carbon content, and acidity of soil. The two sites located near the shoreline were continually flooded from September to January after the lake water level increased by up to 30 cm. Two inland sites were periodically (June–September) flooded by rain water. Flooding at either site caused decreased density of soil macroarthropods, with the effect of lake flooding being more pronounced. Density of soil macroarthropods at flood-affected sites peaked during spring, whereas seasonal changes in density of these invertebrates at most upland sites were less pronounced and peaked in autumn. Results indicated that seasonal migration and recolonization by soil macroarthropods along the moisture gradient are important strategies to overcome flood-affected population losses.

The kipuka system, a network of forest fragments surrounded by lava flows on the island of Hawaii, offers an opportunity to study the natural, long-term fragmentation of a native ecosystem. We examined the impacts of habitat edges upon the community structure of nocturnally active native spiders, primarily in the genus Tetragnatha. We measured plant and spider species distributions across the edges of four small fragments and one large continuously forested area that were surrounded by a lava flow in 1855. Results indicated that an ≈20 m edge ecotone surrounds core forest habitat. Spider community structure changed across the edge, with a decrease in total species richness and diversity at the forest/lava boundary, and a change in the dominant taxon from native Tetragnatha (Tetragnathidae) to native Cyclosa (Araneidae). Severe habitat restrictions were found for some spider species. In addition, nearly all of the spiders captured were endemic species, and the few introduced species were limited to the younger and more open lava flows. Our results suggest that species responses to edges can vary, and that core habitat specialists may decline in fragmented conditions.

In this study, I analyzed the diversity of the dung beetle community (Coleoptera: Scarabaeidae: Scarabaeinae) in relation to its bovine dung-removal efficiency in a cattle ranch with a load of 250 animals currently under holistic resource management. A total of 3,430 individuals of 8 Scarabaeinae species was collected, of which 5 species are abundant in the area: Euoniticellus intermedius (Reiche), Digitonthophagus gazella (Fabricius), Onthophagus mexicanus Bates, O. knulli Howden and Cartwright, and Canthon humectus (Say). Of these 5 species, E. intermedius, D. gazella, and C. humectus were dominant in terms of abundance and biomass. Cattle dung pats were exploited mostly within the first 48 h after deposition. The activity and abundance of dung beetles recorded in the study were insufficient to remove the amount of fresh dung deposited in cattle pastureland.

This study investigated the interactions of the pupal fruit fly parasitoid, Dirhinus giffardii Silvestri, with each of four egg- or larval-pupal fruit fly parasitoids: Fopius arisanus (Sonan), Diachasmimorpha longicaudata (Ashmead), Diachasmimorpha kraussii Fullaway, and Psyttalia concolor (Szépligeti) in Hawaii. F. arisanus attacks host eggs, whereas the other three attack host larvae; all four parasitoids emerge from host puparia. D. giffardii attacked host puparia that had been previously parasitized by all of the other four parasitoids. Attacks by D. giffardii on young fly puparia in which the secondary (parasitoid) host pupae had not fully formed resulted in high offspring mortality of D. giffardii compared with those developing on older host puparia, in which the host pupae had fully formed. Adult D. giffardii that developed on secondary host species were smaller and had higher mortality than those reared from the primary host, the Mediterranean fruit fly, Ceratitis capitata (Wiedemann). Developmental times of male and female D. giffardii were not affected by the host species. D. giffardii preferred to attack older rather than younger host puparia. D. giffardii also preferred to attack the primary rather than the secondary host species and invested more female offspring in primary than in secondary host species. Because of its nature of facultative hyperparasitism, D. giffardii may pose significant nontarget risks to other primary fruit fly parasitoids.

Periplaneta americana (L.) is one of the major hygienic pests distributed worldwide. Evania appendigaster (L.) is a parasitic wasp species of oothecae of P. americana and could, therefore, be used in the control of P. americana. Before releasing the parasitized oothecae, however, it is important to inhibit embryogenesis of P. americana to prevent them from hatching. Hence, the objective of this study was to investigate the effect of four physical treatments (freezing, heating, UV irradiation, and gamma irradiation) on the hatchability of the treated oothecae and also to measure the parasitism rate, emergence rate, and developmental time of E. appendigaster in the treated oothecae. The results revealed that P. americana hatched from UV-treated oothecae, whereas the eggs receiving the other three treatments did not hatch. The results also indicated that, except for the oven-heated oothecae, those receiving the other three treatments had no effect on the parasitism rate of E. appendigaster. In addition, the freezing treatment had the highest impact on the emergence rate and developmental times of E. appendigaster, with <20% emergence. Overall, our results suggested that gamma irradiation had the lowest impact on the parasitism rate, emergence rate, and the developmental times of E. appendigaster. The application of parasitized oothecae to P. americana habitats, such as sewer networks, together with bait control, may effectively reduce the population of P. americana.

This study examined the potential role of native parasitoids in suppressing pest populations of Argyrotaenia citrana (Fernald) in coastal California apple orchards. An initial survey of larval and pupal parasitoids of A. citrana found that the most common parasitoids of A. citrana were the braconid Apanteles aristoteliae Viereck and the ichneumonid Exochus nigripalpis subobscurus Walsh that together parasitized 33% of the A. citrana larvae collected. To identify which parasitoid species caused most host mortality, parasitoid-induced mortality was examined more closely using sentinel A. citrana larvae. Small batches of both newly hatched and older (third and fourth instars) larvae were released and recaptured to collect emerging parasitoids. The results suggested that most parasitoid-induced mortality occurred in young larvae attacked by A. aristoteliae. To determine whether A. aristoteliae would be likely to suppress A. citrana populations in apples, further release–recapture experiments were conducted to assess the parasitoid’s response to host aggregation. A. citrana larvae were released into small patches (individual clusters of fruit) and larger patches (an entire tree) at varying densities. In both the cluster and tree scale experiments the percentage of larvae parasitized by A. aristoteliae remained fairly constant at 40% regardless of the number of host larvae in a patch. These results indicate that A. aristoteliae attacks A. citrana in a density independent manner, which suggests that this parasitoid alone does not exert a strong regulatory effect on summer populations of A. citrana in apples.

The black vine weevil Otiorhynchus sulcatus (F.) is the primary insect pest of field and container-grown woody ornamentals in the Pacific Northwest (PNW). These studies were conducted to determine the natural occurrence of soil-borne entomopathogens in PNW nursery soils and determine their virulence to black vine weevil. Soil samples were collected July–September of 2002 from field-grown woody ornamental nursery stock in Oregon, Washington, and Idaho. Sample collection in each state took place in the major nursery production areas. A total of 280 samples was collected (Oregon, 170; Washington, 50; Idaho, 60). Entomopathogens were isolated using insect baiting (nematodes and fungi) as well as semiselective media (fungi). Bacillus thuringiensis Berliner was isolated through sodium acetate selection. Soil-borne entomopathogenic fungi occur widely throughout the major nursery production areas in the PNW. The entomopathogenic fungi Metarhizium anisopliae (Metchnikoff) Sorokin, Beauveria bassiana (Balsamo) Vuillemin, and Paecilomyces tenuipes (Peck) Samson were isolated. An entomopathogenic nematode (Steinernema oregonense Liu and Berry) and B. thuringiensis were also isolated. Of the 30 fungal isolates bioassayed, all but one was pathogenic to last-instar black vine weevil. None of the B. thuringiensis isolates collected were pathogenic to adult black vine weevil. The S. oregonense that were collected only infected a single black vine weevil larvae at 15 and 22°C. Pathogens collected from this soil survey will serve as a source of potential biological control agents for black vine weevil.

The efficacy of Thripinema nicklewoodi Siddiqi as a biological control agent of Frankliniella occidentalis (Pergande) was tested on caged impatiens bedding plants in a greenhouse. Inoculative releases of parasitized female thrips were made seven times into the caged impatiens preinfested with adult thrips. Two rates were used, one or two parasitized thrips per release date, and impacts on thrips population and flower production were compared with spinosad insecticide treatment and untreated control. Sampling began 9 January 2003 and repeated every 100 degree-days until 4 March 2003. The best thrips control was achieved in the spinosad treatment. None of the four thrips life stages was found at levels higher than 0.09 thrips per flower. Nematode release treatments also reduced thrips population up to 56% for second instars, 72% for adult females, and 62% for adult males, compared with thrips numbers in untreated control cages. However, no difference in reduction of thrips populations was found between the two nematode treatments with different release rates. Both spinosad and nematode treatment cages produced up to 3 and 1.4 times as many flowers compared with the control, respectively. A simpler rearing method for production of T. nicklewoodi also was presented. Using a “thrips-egg-embedded” rolled bean leaf as the transmission arena, 2.7 F₁ parasitized female F. occidentalis were produced for each P₁ parasitized thrips used for inoculum.

The biology of Episimus utilis Zimmerman, a natural enemy of Brazilian peppertree, Schinus terebinthifolius Raddi, was investigated in a quarantine laboratory as part of a classical biological control program against this invasive weed in Florida. Adults lived on average 6.8 ± 0.8 d, and a generation was completed in 43.6 d at a temperature of 22.0°C and a photoperiod of 12:12 (L:D) h. Peak egg production occurred 2 d after females eclosed from the pupal stage. Females deposited a maximum of 172 eggs, with an average daily maximum of 13.6 eggs. The durations of the egg, larval, and pupal stages were 5.9, 23.7 (five instars), and 12.0 d, respectively. Stage-specific life tables were constructed to calculate basic population statistics. Under laboratory conditions where predation and food supply were not limiting factors, a population of E. utilis was capable of multiplying its population by 1.17 times per day, and a doubling of the population would occur every 4.4 d. To date, 10 consecutive generations of E. utilis have been produced on potted Brazil peppertree plants in the laboratory. The potential effectiveness of E. utilis as a biological control agent of Brazilian peppertree in Florida was examined using Goeden’s revision of the Harris scoring system.

When important agricultural pests are omnivores instead of strict herbivores, their impact on the host plant may change as the omnivore shifts between consumption of plants and consumption of prey. Lygus hesperus, a key pest of cotton, is known from laboratory and field studies to be an omnivore, but no field studies have ever quantified the importance of predation as a source of food. Cotton growers have long considered the impact of L. hesperus on cotton to be enigmatic, because sometimes crop damage seems to be higher or lower than would be expected based upon the density of L. hesperus estimated through sweep net samples. Here, we conducted focal observations of L. hesperus foraging freely in the field to quantify the relative importance of predation versus herbivory as food resources and to determine whether omnivory was sufficiently common that it might underlie the “Lygus enigma.” In observations of 84 individuals over a total of 56.7 h, we did not observe any predation events. Observations conducted in the laboratory under continuous magnification also yielded no evidence of predation, suggesting that we were not failing to detect predation events on small or cryptic prey in the field. Thus, L. hesperus expresses predatory behavior at most very infrequently and develops essentially as an herbivore in California cotton. We did, however, find that adult male L. hesperus spend more of their time resting and spend less time on the vulnerable reproductive structures of the cotton plant compared with nymphal stages or adult females. Further work on the Lygus enigma will examine the differential ease of sampling different L. hesperus life stages and the possibility that they contribute unequally to crop damage.

This 2-yr on-farm study was designed to evaluate the ability of grain sorghum, Sorghum bicolor (L.) Moench, to serve as a trap crop for the corn earworm, Helicoverpa zea (Boddie), by attracting corn earworm females into the sorghum as they emerged from cornfields. Three plots of sorghum trap crops and three equally sized plots of cotton, Gossypium hirsutum L., trap crops were planted in a strip between a commercial cornfield and a commercial cotton field. The cotton field adjacent to the trap crop plots was divided into field cotton plots associated with the sorghum trap crop plots and field cotton plots associated with the cotton trap crop plots. Three commercial cotton fields adjacent to corn, but without trap crops, also were sampled. The number of corn earworm eggs per plant and the percentage of plants with corn earworm eggs was higher in the sorghum trap crop plots than in the cotton trap crop plots for both years, demonstrating that corn earworm females preferred to oviposit in the grain sorghum over cotton. A higher percentage of plants with corn earworm eggs was found in cotton in control fields compared with fields with trap crops, indicating that the grain sorghum trap crop was not the source of corn earworm. An economic threshold of 5% corn earworm young (first and second instars) was exceeded more times for cotton in control fields compared with cotton in fields with trap crops. Thus, for two seasons the grain sorghum trap crops helped reduce the need for insecticide applications for this pest. Percentage of parasitization by the egg parasitoid Trichogramma pretiosum Riley and the number per plant of the predator Orius insidiosus (Say) were higher in the sorghum trap crop plots than the cotton plots. However, the grain sorghum trap crop plots were not sinks for these natural enemies. We conclude that grain sorghum could serve as an effective trap crop for corn earworm in cotton.

Migratory adult potato leafhoppers, Empoasca fabae (Harris), have shown a preference for particular cultivars of edible beans, Phaseolus vulgaris L. Laboratory experiments were conducted to determine the role of visual and olfactory cues in these preferences. No preference for any particular cultivar of edible bean was detected in Y-tube olfactometer binary comparison tests: when selecting leaves on the basis of olfactory stimuli. Adult potato leafhoppers chose ‘Berna Dutch brown’ as frequently as ‘Stingray white’ bean and ‘EMP 419’. When adult potato leafhoppers selected leaflets of uniform shape and size from an aerial position in a Plexiglas chamber, ‘Berna Dutch brown’ was significantly preferred (54%) over ‘Stingray white bean’ (24%) and ‘EMP 419’ (22%). An external integrating sphere attached to a portable spectroradiometer was used to determine the wavelength reflectance of ‘Berna Dutch brown’, ‘Stingray white’, and ‘EMP 419’ bean leaflets. ‘Berna Dutch brown’ bean leaflets had higher percent reflectance readings in the green region of the spectrum and lower percent reflectance readings in the blue and yellow regions of the spectrum compared with ‘Stingray white’ and ‘EMP 419’. Although host-finding behavior may involve an interaction between visual and olfactory stimuli, the results of this study indicate that leaf color significantly influences host preference, whereas host odor does not.

We compared the flight behavior of Lygus hesperus Knight and Lygus lineolaris (Palisot de Beauvois) relative to age, sex, and time of day by using tethered (flight mills) and untethered flight (vertical flight chamber) assays. Both species and sexes initiated flights throughout the day, and flight mill assays recorded flights throughout the night. For both species and flight systems, most flights were <5 min in duration, with longest flights occurring from 1 to 3 wk of age. Number of flights and flight duration were influenced by age and sex for tethered individuals and by sex for untethered individuals. Species differences were less apparent, but tethered L. lineolaris had more sustained flights (individual flights >5 min) that were of longer cumulative duration compared with L. hesperus. The longest flights were obtained with flight mills and were 17–18 times longer than the longest flight (22 min) in the flight chamber. Determination of flight periodicity, throughout the day and night, was only possible for tethered insects, and females exhibited more distinct periodicities for sustained flights than males. For L. hesperus females, sustained flights followed a diurnal to crepuscular periodicity, whereas sustained flights by L. lineolaris females were nocturnal. No significant correlations were found between egg load and any of the flight parameters when grouped by species, but there was a positive correlation between the number of spermatophores and several of the flight parameters for female L. hesperus. In the vertical flight chamber, takeoffs began at low light levels and were always higher for L. lineolaris than L. hesperus. Rates of climb toward the skylight cue were ≈50 cm/s, indicating a capacity for strong, self-directed flight by both species.

The purpose of this study was to determine whether preferred prey of Podisus maculiventris (Say) (Heteroptera: Pentatomidae) adult females also conferred maximal fecundity. We also studied egg development and maturation as a function of predator age, i.e., “ovigeny” as used predominantly in the context of parasitoids. To determine prey preference, adult females were simultaneously offered five pest prey: 1) beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae); 2) fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae); 3) cabbage looper, Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae); 4) greater wax moth, Galleria mellonella (L.) (Lepidoptera: Pyralidae); and 5) yellow mealworm, Tenebrio molitor (L.) (Coleoptera: Tenebrionidae) (n = 20). In a second experiment, adult P. maculiventris females were provided a single species of prey (for each of the five prey species, n = 10). This experiment was repeated over four durations: 7, 15, 22, and 30 d. After each time trial, egg load dissections were performed, and numbers of mature and immature eggs were recorded. P. maculiventris displayed a preference of beet armyworm, whether measured as numbers attacked or estimated biomass consumed. However, no significant differences were found in cumulative numbers of eggs laid under the different prey treatments, with the exception of the 22-d trial where significantly more eggs were laid when feeding on the cabbage looper. During the 22-d trial, the number of egg clutches and numbers of eggs per clutch were highest when fed cabbage looper and lowest with yellow mealworm. Percentage of egg hatch combined across time trials was highest in cabbage looper (81.7%) and lowest in greater wax moth (63.8%). Egg load dissections revealed that the total number of eggs and numbers of mature eggs declined significantly with predator age. However, numbers of immature eggs increased. The mean number of mature eggs in 7-d-old predators represented only ≈5% of mean cumulative numbers of eggs laid by 30-d-old predators, indicating that P. maculiventris is strongly synovigenic, where egg development and maturation continues during adulthood. The implications of these results are discussed from the context of P. maculiventris as a biological control agent.

Vision is considered to be an important component of the sensory system used by herbivorous insects to locate host plants. We investigated preferences for transmissive colors and contrasts in the apple blossom weevil, Anthonomus pomorum L., which colonizes apple trees, Malus domestica Borkh., in early spring. The main components of the supposed visual system, green, blue, and UV light, were offered to the weevils versus black or versus each other in a dual choice arena. Furthermore, silhouettes of two different achromatic contrasts were offered in front of the colors blue and green. We also tested whether visual preferences change with time, i.e., 2, 4, and 6 d after termination of diapause in early spring. Female weevils chose UV, green, and blue over black, whereas males only chose UV over black in a series of dual choice experiments. Both sexes preferred blue to green. Weevil response to silhouettes of different contrasts was influenced by the background color, i.e., the silhouette with the higher contrast was preferred in front of green, whereas the silhouette with the lower contrast was preferred in front of blue. The preferences during visual orientation did not change with time after diapause. The more discriminating response of females may reflect a greater visual acuity or a greater visual responsiveness in females than in males because of a higher affinity for the host plant. Our findings indicate that weevils might have a trichromatic visual system and that they are able to include visual cues for the location of host plants in the field.

Various trap types were evaluated for catching western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), and hoverflies (Diptera: Syrphidae). More western flower thrips were attracted to blue (458-nm peak reflectance) sticky card traps compared with yellow (560 nm) or white sticky card traps. Blue light-emitting diodes (LEDs; 465-nm peak emission) increased the efficacy of blue sticky card traps for catching western flower thrips. Numbers of western flower thrips caught on blue flat rectangular card traps were increased 2.0–2.5 times when cards were equipped with blue LEDs. Hoverflies adults are pollinators, and larvae are natural enemies of aphids and other pest insects. Hoverfly adults were attracted to blue sticky card traps. Nylon screen cages effectively excluded the hoverflies from the blue sticky card traps.

Adult Colorado potato beetles, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), released uniformly at densities of 2, 8, 16, and 32 beetles per plant, had an emigration rate independent of initial density per plant. The overwintered (postdiapause) and summer (prediapause) adult beetles emigrated at overall mean rates of 0.403 and 0.398 beetles over the first 4 h after release. The reduction in the mean percentage of released overwintered and summer beetles per plant over a period of 124 h after the initiation of the release followed an exponential decay model. Over that period, the emigration rate of overwintered populations changed faster than that of summer populations. The corresponding immigration rates into beetle-free areas (342.8 m²), which surrounded the RAs (37.4 m²) of the potato plots, were low. The overwintered and summer adult beetles immigrated at overall mean rates of 0.09 and 0.07 beetles over the first 4 h after release. A capture-mark-release-recapture test carried out using the eight beetles per plant density in 1998 showed that cross-contamination of the release plots was not a factor in the study.

Flights of univoltine mole crickets are usually female biased and peak during spring and autumn. A male Gryllotalpa africana Palisot de Beauvois song recording was broadcast weekly at 93.7 dB (200 mm from speakers, 20 μPa) just after sunset for 1.5 h over an annual period. Attracted individuals (conspecifics) were sexed and females were dissected. Temperatures were measured at each sampling date, and moon phase was recorded. Adult G. africana flew to the song broadcast from spring to autumn, with activity peaking mid-spring and again in late summer to early autumn. Spring flights were characterized by a significant female bias, whereas sexes were present in equal proportions during summer and autumn. The monthly sex ratio of flying individuals was not significantly different from that of mole crickets sampled in the field. Flying females were only reproductively mature in spring to early summer and contained eggs beginning in late spring. Eggs per flying female declined into summer. Flight activity and gender of G. africana were significantly positively related to temperature, with air temperature showing the highest degree of correlation. Moon phase showed no significant relationship with the total number of flying individuals or that of genders.

We tested the host specificity of Pseudacteon curvatus Borgmeier from Formosa, Argentina, on North American colonies of the red imported fire ant, Solenopsis invicta Buren, and the native fire ants Solenopsis geminata (F.) and Solenopsis xyloni McCook. No-choice tests showed that P. curvatus hovered over and attacked all three species of fire ants. The number of pupae successfully completing development to adult flies in the trials was 5.03 ± 1.55 (mean ± SE) per female fly in S. invicta, 0.66 ± 0.24 per female fly in S. xyloni, and 0 per female fly in S. geminata. Paired preference tests showed that P. curvatus preferred to hover over S. invicta instead of S. xyloni 77 ± 3% (mean ± SE) of the time and preferred S. invicta over S. geminata 87 ± 4% of the time. The oviposition attempts of active female P. curvatus were 2.8 times higher on S. invicta than on S. xyloni and 16 times higher on S. invicta than on S. geminata. These results demonstrate that this new biotype of P. curvatus is more host specific to North American red imported fire ants than a previous biotype collected from black imported fire ants.

The locomotory activity of both hungry and satiated individuals of Carabus hortensis L. was studied both in pine and beech forest by tracking the beetles by using a portable harmonic radar system. The degree of locomotory activity as well as walking distances was recorded for both males and females. Hungry males and females show a similar degree of activity. When satiated, locomotory activity of females is significantly lower than that of males in both types of forest. These differences in locomotory activity are considered in the context of male-to-female ratios in pitfall catches. It is proposed to use the male-to-female ratio for C. hortensis, and possibly other species, as an indicator of food accessibility in forest habitat: the more males in pitfall catches in relation to females, the better the food situation in the forest.

Plastic UV reflective mulch (metalized mulch) and wheat straw mulch delayed colonization by Bemisia argentifolii Bellows & Perring and the incidence of aphid-borne viruses in zucchini squash. No insecticides were used in either mulch treatment. The mulches were compared with a preplant treatment of imidacloprid and an untreated, unmulched control. In 2000, yield of marketable fruit in the plastic and straw mulched plots was approximately twice that from the imidacloprid plot. In 2001, yield from the straw mulch plots was twice that of the imidacloprid and plastic mulch plots. Yields from both mulched plots and from the imidacloprid plots ranged from 3 to 12 times higher than those from the control plots. The mulches were more effective than a preplant application of imidacloprid in reducing the incidence of both B. argentifolii and aphid-borne viruses. Plants growing over the plastic mulch and the straw mulch grew more rapidly and reached a larger size, as determined by plant dry weight, than did those growing over bare soil, with or without imidacloprid. The spectral quantum flux from the plastic averaged between 80 and 90% of ambient spectral quantum flux values in the UV (300–400-nm) range. Spectral quantum flux values of wheat straw were similar to those of the reflective mulch and ambient near 300 nm but were virtually identical to bare soil beyond 320 nm. The metalized mulch reflected 94% of the incoming photosynthetically active radiation (PAR) in the 400–700-nm range compared with ambient, whereas the straw mulch reflected 85%. Bare soil reflected only 41% of incoming PAR compared with ambient.

Sampling of Lepidoptera-infesting cotton bolls [Helicoverpa armigera (Hübner), Diparopsis watersi (Rothschild), Spodoptera littoralis (Boisduval), and Earias spp.] in Cameroon is based on examination of whole plants. To reduce the time taken by sampling procedures, we studied the suitability of a subsampling plan based on examination of plant terminals. The development of such a subsampling plan requires that the proportion of larvae located on plant terminals should remain constant. However, our study of the within-plant distribution of larvae revealed that their proportion on the five upper fruiting branches was too variable to allow the development of a sampling plan. Examination of the 10 upper branches led to less variable results, but the proportion was still significantly influenced by the pest species and time after crop emergence. We designed a conservative sampling plan in which the proportion was constant and equal to the lower bound of the 90% confidence interval for its predicted minimum (0.594). With this underestimation, the probability distribution of the number of larvae on the ten upper branches of a n plant sample was a compound of a negative binomial and a binomial distribution. These results enabled the design of a sampling plan that reduces sampling time by up to 60%, but the cost of this reduction is an increase in the risk in deciding on intervention when the mean infestation is lower than the critical density.

Insect sampling/monitoring inside grain bins is time consuming, cumbersome during the summer heat in the headspace of grain bins, may require investment in costly sampling devices for sampling of grain, and involves a certain risk to employees. Thus, it is important to explore unbaited sticky traps on the outside of grain elevators as decision support tools for improved management of stored grain. In this study, we analyzed seven trap catch data sets of unbaited sticky trap catches on the outside of grain bins and corresponding probe trap catches in the upper level of the grain mass at three farm bins in 1991, with capacities ranging from 68 to 141 metric tons, and at two commercial steel bins in 1993 and 1994, with capacities of 5,400 and 6,800 metric tons. We used response surface regression analysis to analyze standardized trap catches of the rusty grain beetle, Cryptolestes ferrugineus, and showed that (1) from late June to late July, catches on unbaited sticky traps placed on the outside of grain bins preceded probe traps inside the bins by ≈3 d, which suggested immigration into bins; and (2) in late August, unbaited sticky trap catches on the outside of bins started to decrease, while probe trap catches inside the bins continued to increase until mid-September. We concluded that, from late June to mid-August, immigration of C. ferrugineus individuals into grain bins influences abundance in the upper grain layer, whereas later in the season, the two types of trap catches were only loosely associated. This study is consistent with results published elsewhere that immigration of C. ferrugineus into grain bins initiated shortly after wheat was loaded into the bins.

Oligophagous herbivores that move between host species may face tradeoffs between reduced reproduction and improved dispersal capabilities. We tested the hypothesis that, in oligophagous insects, larvae reared on a suboptimal host will eclose to adults with greater flight tendency but poorer reproductive output than adults that develop on optimal hosts. Accordingly, we studied the effects of larval food on the potato tuberworm, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), an oligophagous herbivore in which some populations seem to have recently increased their host range to include tomato. Larvae that were fed tomato foliage eclosed to adults with a higher tendency to fly (i.e., were more likely to disperse) than those that developed on potato leaves, an optimal host (61.7 ± 8.7 versus 31.0 ± 3.3% were classified as “flyers” when reared on tomato versus potato foliage, respectively). A higher tendency to disperse from poor host plants would retard the evolution of host races in herbivore populations. Variations in larval food plants and in the tendency of adults to fly correspond with female wing loading, energy reserves (lipid content), and reproductive output. We suggest that the effect of host quality on adult dispersal is mediated primarily by biomechanical factors, such as wing loading.

The forest tent caterpillar, Malacosoma disstria Hübner (Lepidoptera: Lasiocampidae), is distributed throughout North American hardwood forests. Although considered polyphagous, regional populations tend to use only a few host species for oviposition, suggesting that M. disstria is more oligophagous than commonly thought. We tested this premise using larvae from Manitoba, Canada; Michigan; and Louisiana in a factorial, reciprocal transplant experiment. Pupal mass, development time, and survival were recorded for each population after rearing larvae in Louisiana on three primary hosts used by southern populations (water tupelo, Nyssa aquatica L.; sweetgum, Liquidambar styraciflua L.; and water oak, Quercus nigra L.) and in Michigan on three northern host trees (red oak, Quercus rubra L.; trembling aspen, Populus tremuloides Michaux; and sugar maple, Acer saccharum Marshall). Manitoba, Canada and Michigan populations had the highest pupal mass, best survival, and most rapid development on trembling aspen and red oak, both northern species. Louisiana larvae attained the highest pupal mass on water tupelo, a primary host across the Gulf States. Northern populations grew poorly on water tupelo, whereas Louisiana caterpillars had the smallest pupal mass and poorest survival on sugar maple. Both red and water oaks were acceptable hosts for all three populations. Our results indicate that M. disstria is actually a composite of regionally adapted populations rather than an extreme generalist. It is unclear, however, what mechanisms might reduce gene flow, allowing such specialization to evolve and persist. We suggest that varying phenology in adult flight times among populations feeding on different hosts could provide at least a partially isolating mechanism, allowing for the evolution of host adaptation.

Lysibia nana Gravenhorst (Hymenoptera: Ichneumonidae) is a solitary hyperparasitoid that attacks newly cocooned prepupae and pupae of braconid wasps in the subfamily Microgastrinae. One of its preferred hosts is Cotesia glomerata L. (Hymenoptera: Braconidae), a gregarious endoparasitoid of white butterfly caterpillars that feed exclusively on plants producing partly inducible glycoside toxins known as glucosinolates. Here, adult body size, egg-to-adult developmental time, and developmental mortality were compared in L. nana reared from prepupae of C. glomerata (the “primary host”) emerging from larvae of Pieris rapae (L.) and Pieris brassicae (L.) (Lepidoptera: Pieridae) that were in turn maintained on two related crucifers, Brassica oleracea L. and Brassica nigra L. (Brassicaceae). Moreover, offspring sex ratio of L. nana reared in the laboratory was compared with that of field populations of C. glomerata reared on P. brassicae. Hyperparasitoids attained larger mass when “originating” from P. brassicae than P. rapae, a pattern that closely reflected host quality for C. glomerata. However, for a given host cocoon mass at parasitism, hyperparasitoid mass was greater on P. brassicae reared from B. oleracea than from B. nigra. Developmental time was more uniform across the different species combinations. Sex ratios in L. nana were higher than in C. glomerata, irrespective of the secondary (herbivore) host. Our results suggest that plant and herbivore quality are important factors affecting the development of L. nana as mediated through the primary parasitoid host. Consequently, both qualitative and quantitative constraints characterize interactions among L. nana and lower trophic levels.

We evaluated the suitability of three grassy weed species, large crabgrass (Digitaria sanquinalis L. Scop.), giant foxtail (Setaria faber Herrm.), and barnyardgrass (Echinochloa crus-galli L. Beauv.), and a forage grass, tall fescue (Festuca arundinacea Schreb.), along with maize (Zea mays L.), as hosts of the northern corn rootworm, Diabrotica barberi Smith & Lawrence. Potted greenhouse plants were infested with northern corn rootworm eggs, and after hatch, larvae were recovered over time by using Tullgren funnels. The percentage of larvae recovered varied significantly between species at each sample date. The highest percentage of larvae were recovered from barnyardgrass, maize, and large crabgrass followed by giant foxtail and tall fescue. When sample dates were combined to test the main effect of species, there was no significant difference in the percentage of larvae recovered between maize and three other species (barnyardgrass, large crabgrass, and giant foxtail). The change in head capsule width (growth to new instars) also varied significantly between grass species on the second, third, and fourth sample date, but not the first. On the second sampling date, most of the larvae from maize were third instars, and their head capsule width was greater than the head capsule width of larvae recovered from any of the other species. Although the greatest percentage of larvae was recovered from barnyardgrass, larval development on this species was reduced, because average head capsule width of larvae recovered from all sample dates indicated they were mostly second instars. Average larval weights were not impacted by the grassy weed species evaluated. In a laboratory experiment, we studied the host-searching behavior of neonate larvae, in which the movement patterns were traced after contact with and removal from the roots of different species. In this study, we included the above-mentioned species, side-oats grama (Bouteloua curtipendula Michx. Torr), sorghum (Sorghum bicolor L.), and moistened filter paper, which served as a control. There were significant differences in the area searched, number of turns, path crossings, and the average velocity of the northern corn rootworm neonate larvae exposed to the different plant species and the control. The importance of the results in relation to resistance management is discussed.

Larval performance of the cottonwood leaf beetle, Chrysomela scripta F., was evaluated in relation to genetic variation in phytochemical characteristics among first year micropropagated ramets of five aspen clones (Populus tremuloides Michx.). Foliage from the juvenile ramets used in this experiment exhibited moderate variation in nitrogen, phenolic glycosides, and condensed tannin concentrations among clones, and overall, had very high levels of phenolic glycosides (15–22% dry weight) and low levels of condensed tannins (4–6% dry weight). Results from performance assays indicate that genetic differences among aspen clones resulted in only marginal differences in larval performance of this specialist leaf beetle. Although tannin levels were quite low in the juvenile trees, larval growth rate was reduced by 30% with increasing condensed tannin concentrations (R² = 0.209). Recent evidence suggests that aspen undergoes ontogenetic shifts in foliar concentrations of secondary metabolites resulting in decreased phenolic glycoside and increased condensed tannin concentrations as trees age. The high phenolic glycoside and low condensed tannin phytochemical profile of juvenile aspen appears to make it an ideal host for cottonwood leaf beetles.