The behavior and biochemical adaptations of 3 generalist insect species (Tettigonia viridissima L., Ruspolia nitidula Scopoli, and Conocephalus discolor Thunberg) and 3 specialists (Galeruca tanaceti L., Chrysolina geminata Payrtull, and Cloantha perspicillaris Boisduval) to the hypericin-containing leaves of Hypericum perforatum were investigated in southwestern France. The generalists preferentially fed on the part of the leaf lacking the phototoxic, hypericin-laden dark glands. The specialists showed no discriminatory feeding pattern but exhibited a negative phototaxis that is presumed to be an efficient strategy to circumvent the light-induced toxicity of hypericin. The constitutive and hypericin-inducible activities of glutathione reductase and glutathione S-transferase, 2 antioxidant enzymes which are considered to be biochemical adaptations used by phytophagous insects to attenuate the oxidative stress caused by photosensitization, were determined in the fatbody and midgut of T. viridissima, C. discolor, G. tanaceti, and G. geminata. The specialist insects had lower constitutive activities of glutathione S-transferase and glutathione reductase than the generalists, although the application of hypericin induced the activity of glutathione S-transferase in specialist insects only. Insects with different lifestyles therefore are capable of circumventing the phototoxic effects of hypericin by appropriate behavioral and biochemical strategies.

Water-soluble root extracts of the Mexican marigold, Tagetes minuta L., composed mainly of the compounds alpha-gurjunene, 5-(But-3-ene-1-inyl)-2,2′-bithiophene, palmitic acid, alpha-terthienyl, and 5-(4-Acetoxy-1-butenyl)-2,2′-bithiophene, were assessed to determine their impact on six species of nontarget aquatic invertebrates. Test organisms were collected from a polluted stream—Gammarus lacustris Sars (Amphipoda)—as well as from a local nearly pristine stream—Lepidostoma pluviale (Milne) (Trichoptera), Drunella grandis (McDunnough) (Ephemeroptera), Baetis tricaudatis (Dodds) (Ephemeroptera), Rhithrogena morrisoni (Banks) (Ephemeroptera) and Hydropsyche cockerelli (Banks) (Trichoptera). Root extract of T. minuta, formulated with a commercial combination of petroleum solvents and surfactants, caused mortality to some of the organisms tested. Some mortality was attributable to presence of the inert, surfactant/petroleum-based solvent. For example, with L. pluviale, the LT₅₀ for 4 ppm marigold root extract formulated with 0.01 ppm inert materials was 54.7 h (CI 48.1, 64.2), and for 0.01 ppm inert materials alone was 69.8 h (CI 55.8, 101.2). Of the macroinvertebrates tested, R. morrisoni was the most sensitive to inert materials (LT₅₀ 0.01 ppm inert = 4.5 h) and G. lacustris was the least sensitive (LT₅₀ 0.01 ppm inert = 400 h; LC₅₀ 96 h = 1.2 ppm). Marigold root extracts did have a toxic effect at the highest concentration (4 ppm) used on all macroinvertebrates tested. Although previous studies reported the effects of one compound in the root extract, alpha-terthienyl, our research is the first published report evaluating effects of full-formulation marigold root extract on immature aquatic nontarget insect species and a crustacean. If root extracts of T. minuta are to be used as a pesticide, further research should focus on effects of inert surfactants used in marigold extract formulation on nontarget macroinvertebrates.

The root weevil Diaprepes abbreviatus (L.) was reared on artificial diet under controlled conditions of temperature and humidity. The lower thermal threshold for development of neonate larvae was estimated to be 15°C. The growth rate of neonate larvae increased exponentially with increasing temperature up to 30°C. The growth rate of later instars, however, was suppressed at 30°C and mortality was higher than that of larvae reared at 26°C. Larvae reared as late instars only (>56 d old), or continuously at 30°C, had increased mortality and produced smaller adults than larvae reared at 22 and 26°C. Larvae reared as late instars only (>56 d) or continuously at 22°C had similar survival rates compared with those reared at 26°C, and they emerged as larger adults compared with larvae reared at 26 or 30°C. The time required for development from neonate to pupation was 125 ± 3 d (mean ± SEM, n = 38) at 26°C. Duration of the pupal stage was inversely proportional to temperature between 22 and 30°C. Pupal mortality was higher at 30°C than at 22 or 26°C. The total time required for a single generation from oviposition to adult emergence was estimated to be 154 d at 26°C and adequate humidity. Cumulative mean air and soil temperatures and rainfall for a location in central Florida were analyzed and presented for the period October 1991 through January 1999.

Laboratory studies were conducted during the winters of 1996 and 1997 to determine the cold tolerance of overwintering adult bean leaf beetles, Cerotoma trifurcata (Förster). Second-generation adults were collected during early September from soybean fields near Ames, IA. The collected beetles were reared at 24°C with a photoperiod of 10:14 (L:D) h in the laboratory for 3 wk. The beetles were transferred to a chamber with high relative humidity at 5°C and photoperiod of 9:15 (L:D) h for evacuation of gut contents dangling. After 2 wk at 5°C, the beetles were selected randomly and subjected to cold baths maintained at temperatures, including −15, −10, −5, 0, and 5°C. At certain time intervals, beetles were retrieved from the cold baths for the observation of mortality. More than 50% of the adult beetles survived over hundreds of hours at −5, 0, and 5°C, whereas most of the beetles died after 15 min at −10 and −15°C. The results indicated that the critical temperature range causing significant mortality of the overwintering beetles would be between −5 and −10°C. Moreover, during the two-winter study the daily leaf litter mean temperature recorded in woodland mainly stayed at above −5°C. The results showed that hibernating in the leaf litter of woodland allowed the beetles to avoid extreme temperature fluctuations during winter.

We investigated the effects of carboxylic acids on the oviposition behavior of the spruce budworm, a major defoliator of coniferous forests in North America. Carboxylic acids have been implicated as semiochemicals involved in lepidopteran host finding and oviposition, and they occur as free acids in the epicuticular wax of host (Picea and Abies spp.) foliage where spruce budworm lay eggs. In a dual-choice laboratory bioassay, several straight chain and cyclic monocarboxylic acids, and two dicarboxylic acids, significantly enhanced oviposition. Peak activity was associated with saturated acids having 8–12 carbons. Unsaturated oleic and linoleic acids were also preferred. The lowest effective dosage occurred at 7.8 nmol/cm² (1 mM solution). At higher dosages (≥780 nmol/cm²), C₉–C₁₀ acids became strongly deterrent and some shorter-chain and longer-chain acids became stimulating. Electroantennogram responses to C₆–C₁₆ acids indicated that behaviorally active acids are detected by olfaction. The most active acids (C₈–C₁₂ and oleic) have not been reported in the free fatty acid fraction of host cuticular waxes. However, long-chain C₁₄–C₂₈ acids are present as free acids, but they elicited significant oviposition responses only at doses that exceeded their levels in foliage waxes. Spruce budworm preference for carboxylic acids may represent a nonspecific response common to Lepidoptera, which may have evolved because of the ubiquitous occurrence of carboxylic acids in plants.

Experiments were performed to determine the role of the leafhopper Sophonia rufofascia (Kuoh & Kuoh) in damage observed on forest and watershed plants in the Hawaiian Islands. Laboratory manipulation of leafhopper populations on fiddlewood, Citharexylum spinosum L., caused interveinal chlorosis and vein browning on young fully expanded leaves similar to that observed on leafhopper infested plants seen in the field and necrosis on older leaves. Field studies with caged “uluhe” fern, Dicranopteris linearis (Burman), demonstrated that frond veins turned brown within 2 d of leafhopper feeding; and by 141 d after feeding, an average of 85% of the surface area of the fronds were necrotic compared with only 12% necrosis in untreated cages. Field trials with stump-cut firetree, Myrica faya Aiton, were performed to determine the effect of leafhopper feeding on new growth. Our studies showed that the new growth in exclusion cages had significantly greater stem length and diameter, a higher number of nodes, fewer damaged leaves, and almost twice as much leaf area compared with plants caged but with the sides left open to permit leafhopper access. Microscopic examination of sections through damaged areas of several leafhopper host plants showed vascular bundle abnormalities similar to those associated with hopperburn caused by potato leafhopper, Empoasca fabae (Harris), feeding on alfalfa. On Hawaiian tree fern, Cibotium splendens (Gaudichaud), oviposition into the midvein also disrupted vascular bundle integrity and often caused death of the distal portions of the pinnule.

To determine whether the probability of parasitoid attack differed across years, seasons, sites, host plant species, and herbivore feeding modes, leaf-chewing insects (Lepidoptera) that feed on Quercus alba L. and Q. velutina Lam. were collected four times in the Missouri Ozarks (May, June, July, and August–September) in each of the years 1993–1995 and reared in the laboratory. Parasitism rates at a given census were relatively constant from year to year and decreased as the season progressed from May to September: 30% of the herbivores collected in May were parasitized, whereas <15% were attacked in the summer and fall. Similarly, parasitism rates were predictable based on host plant (higher on Q. velutina than on Q. alba) and feeding guild (higher for leaf miners than for external feeders, leaf tiers and leaf webbers, in the summer and fall). Leaf rollers encountered in May had the highest probability of being parasitized. There was also significant variation in parasitism rates among sites. Community composition during the spring was very similar among spring censuses across years and different from all other censuses. In contrast, in the summer and fall, the species assemblage of the parasitoid community remained relatively constant within a year despite the fact that the herbivore community composition changed across censuses.

Larvae of the wheat stem sawfly, Cephus cinctus Norton, feed and complete their development within the lumen of wheat and other hollow-stemmed grasses. Stems with large diameters are preferred and are the most suitable hosts. The sex ratios of wasps are male-biased in small stems and female-biased in large stems. Sawfly fitness, as indicated by wasp size, fecundity, and longevity, increases with host stem size.

We studied responses of ant communities to shrub removal and intense pulse seasonal grazing by domestic livestock for four consecutive years. Weighted relative abundance and percent of traps in which an ant species occurred were analyzed using randomized complete block design, split in time analysis of variance to test for significant differences between means of ant groups. The ant community in the Chihuahuan Desert grassland is dominated by small, liquid-feeding ants, Conomyrma insana (Buckley), and large seed harvesting ants, Pogonomyrmex desertorum Wheeler. The weighted relative abundance of C. insana was significantly reduced on the plots without shrubs. The relative abundance of P. desertorum was significantly lower on grazed plots without shrubs than on the ungrazed plots without shrubs. There were no detectable effects of shrub removal or intense, pulse grazing on the less abundant ant species. These results suggest that the recent encroachment of shrubs into Chihuahuan Desert grasslands has increased the relative abundance of the dominant ant species in these communities. Intensive grazing by livestock has had an adverse effect on the most abundant seed-harvester, P. desertorum.

More than 40 species of herminiine noctuids occur in eastern forests. Nearly all of these are detritivores, skeletonizing fallen leaves and thereby accelerating nutrient cycling in forest ecosystems. Larval feeding assays were conducted for 8 herminiine genera with air-dried leaves from 10 tree and shrub genera. Survivorship was high on dead foliage of Carya ovata (Juglandaceae), Larix decidua (Pinaceae), Prunus serotina (Rosaceae), Quercus alba and Q. rubra (Fagaceae), Vaccinium corymbosum (Ericaceae), and Vitis sp. (Vitaceae); intermediate on Acer rubrum (Aceraceae) and Rhus glabra (Anacardiaceae); and low on Liriodendron tulipiferum and Pinus strobus (Pinaceae). Additional larval feeding assays were performed using Quercus alba leaves treated with an antibiotic, fungicide, and a combination of the two. Treatment with the cell-culture grade antibiotic had no effect on survival of Chytolita morbidalis (Guenée) larvae. In fact, mean pupal weights were significantly greater for larvae fed treated leaves. Treatment with the general purpose fungicide Daconil lowered the survival of C. morbidalis. Given that several species were able to complete their development on air-dried foliage, we suspect that many herminiines are not dependent on the epiphytic bacteria and fungi on leaf litter, as has been suggested by other studies.

The cereal aphids Rhopalosiphum padi L. and Sitobion avenae (F.) coexist on the same host plant but occupy different ecological niches. R. padi arrives first in the season and reaches its population peak before S. avenae. In addition, R. padi prefers the stem and lower leaves, whereas S. avenae is found mostly on the ears and upper leaves of the plant. In greenhouse experiments, the likelihood of competition between R. padi and S. avenae on wheat seedlings and tillering plants was evaluated. The reproductive rate of S. avenae on tillering plants was negatively affected by previous infestation by R. padi, and this effect was larger when R. padi infestation started at an earlier plant growth stage. Likewise, previous infestation by R. padi decreased S. avenae reproduction on seedlings. In contrast, previous infestation by S. avenae on the flag leaf of flowering plants did not affect R. padi on that plant part. When both aphid species co-occurred from the beginning, the presence of either aphid species negatively affected the reproductive rate of the other. R. padi consistently had a higher rate of population increase than S. avenae. The presence of the other aphid species did not affect within-plant aphid distribution or alate aphid production. Results were similar on wheat seedlings and tillering plants. Finally, alate S. avenae preferred uninfested seedlings over R. padi-infested ones, whereas no preference was observed when the experiment was performed with tillering plants.

The development of whitefly control tactics that provide a safer alternative to using pesticides requires a thorough understanding of the interaction between these insects and their host plants. In this study, we investigated the effect of leaf age of zucchini, Cucurbita pepo L., on the oviposition site selection and on the development and survival of immature Bemisia argentifolii Bellows & Perring. Also, we evaluated the effect of squash silverleaf symptoms on adult alighting and oviposition site selection, and on the development of immatures. Whiteflies oviposited significantly more on younger, hairier leaves than on older leaves when tested in a dual-choice petri dish clip cage. Time to 50% emergence was longer on younger versus older leaves, yet survival of immatures did not differ statistically between the leaves tested. In free-flight choice experiments, whiteflies (male and female) alighted significantly less frequently on silverleaf-affected plants than on healthy green plants. However, in dual-choice oviposition experiments, whiteflies did not discriminate between silvered and healthy green leaves. Further experiments revealed no differences in the development of immature B. argentifolii on healthy and silvered leaves. This indicates that the chemical and physiological changes in silverleaf-affected leaves do not have a detrimental effect on the survival or development of whitefly nymphs.

The western corn rootworm, Diabrotica virgifera virgifera LeConte, has altered its movement in east-central Illinois to lay eggs in soybean fields, thereby reducing the effectiveness of crop rotation for western corn rootworm control. Because western corn rootworm larvae cannot survive on soybean roots, adult western corn rootworm population dynamics in these fields is governed by aerial movement. Malaise trap samples from soybean fields were used to describe temporal variation in western corn rootworm immigration and emigration during 1997, 1998, and 1999. Sixty-eight percent of western corn rootworm collected in the soybean fields were female. A diel periodicity in western corn rootworm immigration and emigration was observed on days conducive to beetle flight in soybean fields. Flight activity was low during the early morning (500–700 hours solar time) when air temperatures were cool. Aerial movement peaked between 7000 and 1100 hours. During the first half of this interval (700–900 hours), immigration of western corn rootworm to the soybean field exceeded emigration, thereafter emigration exceeded immigration. Before sunset (1700–1900 hours), flight activity increased. Western corn rootworm were not caught in the malaise traps between sunset and sunrise. Micrometeorological measurements from days when western corn rootworm captures were large indicate that western corn rootworm movement may be gated to late morning, when wind speed and air temperature gradients above the soybean crop frequently create unstable atmospheric conditions that facilitate flight. Because of the diel periodicity and high day-to-day variability of western corn rootworm movement to soybean fields, scouting tools, such as sticky traps and vial traps that integrate captures over an entire day or multiple days, are likely to provide more reliable western corn rootworm population estimates in soybean fields than sampling techniques that measure western corn rootworm abundance at single points in time (e.g., plant counts and sweep net samples).

The foraging behavior and pollinating efficacy of Osmia cornuta (Latreille) and Apis mellifera L. were studied in an orchard of ‘Delicious’ apple, Malus domestica Borkh, in northeastern Spain. Yields after one single visit were more than five times higher in flowers visited by O. cornuta than in those visited by A. mellifera nectar gatherers. This is attributed to the lower rate of stigma contact in A. mellifera visits, rather than to insufficient deposition of compatible pollen when the stigmas are contacted. A. mellifera pollen collectors had very high rates of stigma contact, but they were very scarce (3%) on ‘Delicious’ flowers despite the presence of abundant brood in their hives. One single visit per flower by O. cornuta produced commercial fruit set (27.4%) and fruit size (>70 mm diameter). Based on cell production, average number of trips required to provision a male and a female cell, and flower visiting rates, it is estimated that a mean of 22,252 apple flower visits per female O. cornuta were made during the 15-d flowering period. This result indicates that 530 nesting O. cornuta females per hectare are enough to provide adequate apple pollination.

Mark-release-recapture studies were conducted to estimate foraging populations, maximum foraging distances between foraging sites, and minimum total foraging distance for three colonies of two cuticular hydrocarbon phenotypes of Reticulitermes at a wildland site near Placerville, CA, in the Sierra Nevada foothills and for six colonies of three phenotypes at two residential sites in Marin County. At Placerville, the hydrocarbon phenotype B colony had the fewest termites, with an estimated foraging population of 4,476–13,602, and occupied only one monitoring station. The two phenotype A colonies had foraging populations estimated to range from 40,809 to 128,597; one inhabited one monitoring station, whereas the other occupied three stations with a maximum distance between monitoring stations of 6.3 m. At the Marin County sites, two phenotype D colonies were estimated to have foraging populations ranging from 9,191 to 194,692; each foraged at a single monitoring station. Estimated foraging populations for the three phenotype A′ colonies ranged from 71,483 to 491,901 with the maximum distance between monitoring stations ranging from 11.7 to 25.3 m. The phenotype A colony was estimated to have 8,747–25,190 foragers, with a maximum distance between monitoring stations of 1.8 m.

Cultivars of wheat, Triticum aestivum L., were assessed to determine their respective level of resistance to lesser grain borers, Rhyzopertha dominica (F.), in postharvest storage. Cultivars were representative of hard red winter, soft red winter, white spring, and durum wheat classes currently grown in the United States. Samples of each cultivar were maintained at 30.0°C and 70% RH and infested with 2- to 3-wk-old adult beetles for 1 wk. Adult progeny were counted at the end of one life cycle. Two temperatures, 27.0 and 34.0°C, were studied to examine the role of temperature (calculated in degree-days) in development. This experiment was conducted three times under similar conditions. Cultivars harboring a large quantity of progeny were considered more susceptible than those cultivars in which fewer progeny completed their life cycle. Each cultivar was analyzed for single kernel properties such as hardness, protein, and diameter. Wheat cultivar had a significant influence on quantity of progeny in all experiments. There were no significant effects on survivorship of progeny as a result of temperature when calculated in degree-days. Cultivars with smaller kernels were more susceptible to development of larger generation sizes in experiment 1 but not in the other two experiments. A kernel size experiment using large and small kernels from the same cultivar suggested that larger quantities of progeny are produced on small kernels compared with large kernels. Individual beetle weights were not influenced by temperature or cultivar. These results imply that stored grain managers should be aware of potential differences in susceptibility, attributable to wheat cultivar, to lesser grain borer infestations.

Long-term growth and survivorship of individual arboreal nests were studied in three species of Neotropical termites in the genus Nasutitermes. Of the 29 N. corniger (Motschulsky) and seven N. ephratae (Holmgren) nests monitored in an area of young second-growth in Panama, 12 (41%) N. corniger and four (57%) N. ephratae nests remained active throughout the 9- to 11-mo study. There was no significant difference in survivorship between small and large nests of either species. In surviving N. corniger nests with a single queen, the net increase in volume was highly correlated (r = 0.87, n = 9) with queen wet weight. There was a marked seasonality to nest expansion in both N. corniger and N. ephratae, with growth occurring almost exclusively during the wet season. Seventeen N. acajutlae (Holmgren) nests were monitored for 4–9 yr on Guana Island, British Virgin Islands. Four of the 17 (23.5%) N. acajutlae nests survived the study period, and two more abandoned their original nest and relocated. Within this limited sample of colonies, N. acajutlae nests that were large (>150,000 cm³) at the beginning of the study had a higher probability of survival than did small (<100,000 cm³) nests. Nest budding, relocation, and resprouting are mechanisms that Nasutitermes may use to create a new nest for all or a portion of an established colony. The ontogeny of incipient Nasutitermes colonies is discussed as a sequence in which a young colony remains cryptic within wood, building its population size to a point where the colony can maintain and defend a nest. Early in a wet season, termites then venture from within wood to build and occupy a small arboreal nest.

The development, reproduction, and life table of Amblyseius womersleyi (Schicha) were studied at temperatures ranging from 16 to 38°C, 60–70% RH, and a photoperiod of 16:8 (L:D) h. Mortality of A. womersleyi was high in the early developmental stages, and this trend was especially apparent at low temperatures. The developmental threshold for all immature stages was 11.6°C. The total preimaginal developmental time ranged from 48.3 to 316.0 h. The optimal temperature for development was 33°C. The nonlinear shape of temperature development was well described by the modified Sharpe and DeMichele model. The normalized cumulative frequency distributions of developmental times for each life stage were fitted to the three-parameter Weibull function. The 50% adult survivorship occurred at 15-21 d at ≤24°C, and on 7–9 d at ≥29°C. The mean daily fecundity ranged from 0.325 to 2.963 eggs and was fitted by a third-order polynomial equation. The intrinsic rate of increase (r_m) ranged from 0.053 to 0.402, and was maximal at 33°C. The results of this study indicate that A. womersleyi appears better adapted to higher temperatures, and may be a useful biological control agent for spider mites in greenhouse horticultural crops, and in field horticultural crops during summer. The established functions should be useful in building an A. womersleyi population model.

The nymphal and adult life stages of the tick Ixodes pacificus Cooley & Kohls are the primary vectors of the causative agent(s) of Lyme disease in the far-western United States. In contrast to I. pacificus adults, data on the extent of spatial and temporal variation in the density of the nymphal stage have been scarce. Therefore, we compared the density of I. pacificus nymphs from 1997 to 1999 at a small rural community at high risk for Lyme disease (CHR) and the University of California Hopland Research and Extension Center (HREC), Mendocino County, CA, I. pacificus nymphs were collected readily by drag sampling in leaf litter but not from low vegetation. The mean number of questing nymphs per 100 m² in leaf/fir-needle litter areas from late April to early June differed significantly among years at both the CHR and the HREC. Climatic data from the HREC suggested that yearly nymphal densities in this area may be positively correlated with the amount of rainfall and negatively correlated with maximum temperatures from March to May. Further, nymphal density was two to four times higher at the CHR than the HREC in all 3 yr. Yearly mean nymphal density generally differed two- to four-fold (HREC) and 10- to 20-fold (CHR) among individual sampling areas. Also, two- to three-fold differences in mean nymphal density were frequently observed between continuous litter and litter edges bordering on other habitats within sampling areas at the HREC, and between sampling areas <100 m apart at the CHR. The distributions of nymphs within individual areas were generally aggregated at both the HREC and the CHR, at the 15-m sampling transect scale we used. Environmental factors with some potential to predict the density of I. pacificus nymphs at different spatial scales included climatic conditions, topographic exposure, and presence of habitat edges or logs. However, stepwise multiple regression analysis revealed that only 6.2–18.0% (HREC) or 14.9–27.9% (CHR) of the yearly variation in nymphal densities was explained by the abiotic or biotic traits measured in this study, at the 15-m transect scale. Thus, other abiotic or biotic traits that we did not examine (e.g., local densities of tick hosts) must account for most of the spatial variation in nymphal density.

Many preference and performance studies have been done on latent species of insect herbivores, but few studies have examined whether eruptive species exhibit preferences for oviposition sites that affect larval survival. We used choice experiments to test whether female moths of an eruptive species (the western spruce budworm, Choristoneura occidentalis Freeman) exhibited oviposition preferences for needle age class, for age of host trees, and for host vigor among individuals of one species, Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco. We also evaluated oviposition preferences among three common host species (Douglas-fir, white fir, Abies concolor Lindl., and Engelmann spruce, Picea engelmannii Parry). Females laid more egg masses on older branches (45–60 yr old) than on younger branches (10–15 yr old) of Douglas-fir trees. Also, proportionately more eggs were laid on branches from white fir than on branches from Douglas-fir or Engelmann spruce. There were no differences in the distribution of egg masses when females were offered a choice between 1- and 4-yr-old Douglas-fir needles or between long and short shoots of Douglas-fir. These general patterns were obtained across two generations. However, there were no differences in viability of the F₁ or F₂ egg masses or weights of F₁ female pupae (i.e., fecundity) among treatments for any experiment. Consequently, although female moths of this eruptive species appeared to use foliar cues to determine oviposition sites, we could not link these preferences to any effects on offspring performance because performance did not vary. This contrasts with the tight linkages between preference and performance documented for many latent species.

Increasing altitude may influence insect communities, population sizes, life-histories, and morphology. Nicrophorus investigator Zetterstedt, a holarctic species, occurs over a range of elevations in the western Rocky Mountains of North America. This study examines changes in population density, seasonal activity periods, morphology, and reproduction at three sites over an elevational gradient in the southern Rocky Mountains of Colorado. N. investigator population sizes varied yearly at both low (≈2,800 m) and high (≈3,200 m) elevations, but were always greater at the lower elevations. Adult activity at all sites began in late June, remained relatively constant throughout July, and declined by late August. Elytron length was highly correlated both with body mass and pronotum width. There was no difference in elytron length between males and females (within years, sites). However, elytron length was significantly greater in 5 out of 6 yr at the higher elevation site, and in 1999, at two additional low and high elevation sites in separate drainages. Beetles at the low and high elevation sites differed slightly in their reproductive strategies under captive conditions. At the high elevation, the number of larvae did not increase with carcass size, thus larvae from larger carcasses weighed more than larvae reared on smaller carcasses. At the low elevation, brood size tended to increase with carcass mass, resulting in similar-sized larvae across all carcass masses. On average, brood growth efficiency (total brood grams/carcass grams) was higher at the higher elevation, perhaps explained by developing at lower temperature. These results indicate that both life-history strategies and developmental processes may be involved in the elevational variation seen in this species.

We found that leaf pubescence in Sassafras albidum (Nuttall) Nees negatively influences the growth and survivorship of a lepidopteran herbivore, Papilio troilus (L.). S. albidum leaves varied greatly in pubescence among plants. In laboratory choice experiments, P. troilus larvae preferred to eat and adult females preferred to oviposit on nonpubescent S. albidum leaves. Larvae fed pubescent S. albidum had slower growth and higher mortality in early instars than larvae fed on nonpubescent leaves. These negative effects of pubescence on adult oviposition, larval growth rate, and larval survivorship suggest that the population size of P. troilus will reflect availability of nonpubescent hostplants. In field surveys, the frequency of pubescent S. albidum was significantly greater in open habitats created by harvesting pine forest than in hardwood forests, perhaps because of higher light and lower moisture in open areas. By changing the availability of quality food resources, forest management may have unintended negative impacts on this butterfly population.

The importance of host plant effects on aphids, and their natural enemies, has been well documented. However, few studies have isolated the mechanisms that determine suitability of insect prey among host plants for the survival and development of predators. We evaluated the nutritional interactions among alfalfa, Medicago sativa L. ‘OKO8’, and faba bean, Vicia faba L. ‘Windsor’, host plants, pea aphid herbivores, Acyrthosiphon pisum (Harris), and a lacewing predator, Chrysoperla rufilabris Burmeister. The survival and development of lacewing larvae supplied with five daily levels (1.2–16.4 mg) of pea aphids reared on either alfalfa or faba bean were documented. Compared with aphids reared on faba bean, those reared on alfalfa stored 6.3 times greater levels of myristic acid resulting in a 2.7-fold increase in total fatty acid content (micrograms per milligram of aphid weight). This increase in total fatty acids equated to an ≈1.3-fold increase in available calories for C. rufilabris provided with pea aphids reared on alfalfa. There were no statistical differences among treatments in the ratio of lacewing individuals surviving to the pupal or adult stage. The ratio of deformed lacewing adults increased with decreasing daily prey levels, and this increase was greatest for C. rufilabris supplied with pea aphids reared on faba beans. Lacewing larvae supplied with pea aphids reared on alfalfa had faster developmental rates (1/d) than C. rufilabris larvae supplied with pea aphids reared on faba beans. Interestingly, these differences in developmental rates between host plants continued to occur after the rates plateaued at the highest daily prey level. The separation of C. rufilabris developmental rates between host plants at low and high daily pea aphid levels does not support the hypothesis that quantitative differences in the nutritional value of pea aphids, as influenced by differences in fatty acids and calculated nutrition levels (calories) between pea aphids reared on separate plant hosts, were responsible for differences in C. rufilabris developmental rates. Rather, separation of developmental rates at low and high daily prey levels, and no statistical interactions between daily prey levels and host plants, suggest qualitative differences in the nutritional value of pea aphids between host plants.

We compared the severity of insect problems in early and conventional soybean, Glycine max (L.) Merrill, production systems in the mid-South. The conventional soybean production system (cultivars in maturity groups V–VII planted in May) experienced significantly higher populations of late-season defoliators than the early soybean production system (cultivars in maturity group IV planted in April). However, the early soybean production system harbored significantly larger populations of southern green stink bug, Nezara viridula (L.) and threecornered alfalfa hopper, Spissistilus festinus (Say). Predators were significantly more abundant in the early soybean production system compared with the conventional soybean production system, early in the growing season. Late in the growing season, predator populations were lower in both productions systems and differences between the two systems were not significant. The results from the current study illustrated the benefits of early-planted early-maturing cultivars (early soybean production system) in avoiding lepidopterous and coleopterous defoliators that occur late in the growing season. However, our data also indicate that arthropod management will be essential in the early soybean production system because widespread use of this system will result in an abundance of suitable hosts for early-season pests.

Particle film technology is aimed at controlling both arthropod pests and diseases of plants with a hydrophobic particle barrier primarily composed of kaolin. Field studies were conducted from 1996 to 1998 to compare the efficacy of dust and liquid applications, and hydrophobic and hydrophilic particle films, against key pests of pear. In addition, the effects of particle film applications on pear yield and quality were investigated in 1998. Dust and liquid applications of hydrophobic and hydrophilic particle films obtained high levels of early-season pear psylla control and prevented pear rust mite damage. We also found that prior seasonal applications of particle films in 1997 can carry over into the 1998 season to suppress early season pear psylla oviposition. A major concern in the shift from hydrophobic to hydrophilic particle films was the loss of disease control. We found that a water-repellant particle film was not required to control the fungal disease fabraea leaf spot. Pear yields were nearly doubled by liquid formulations of hydrophobic and hydrophilic particle films. Particle film deposits were measured using a spectrophotometer method we developed. Particle deposition differed among formulations for both leaf age and leaf surface (top or bottom). Yet, the particle formulations performed about the same against insects and fungal diseases, and in how they influenced the horticultural traits. None of the particle film formulations were found to be phytotoxic to pear foliage or fruit during the study period. A shift from hydrophobic to hydrophilic particles makes it possible to more easily formulate and disperse the particles in water so that conventional spray equipment can be used. The multifunctionality and low toxicity of particle films could make them an attractive alternative to conventional pesticides.

Analyses of pitfall traps in Washington and Oregon apple orchards revealed that highly mobile invertebrates were strongly susceptible to applications of broad-spectrum, neural-active insecticides. When compared with orchard blocks managed without broad-spectrum insecticides, orchard blocks under conventionally managed regimes had significantly lower populations of ground beetles (Coleoptera: Carabidae), centipedes (Chilopoda), earwigs (Dermaptera: Forficulidae), harvestmen (Opiliones), and spiders (Aranae). The carabid species Pterostichus adstrictus Eschscholtz and P. melanarius Illiger constituted 89% of all ground beetles collected over 2 growing seasons. Three times as many free-hunting spiders were found in the no broad-spectrum blocks than in the conventional blocks. Less mobile invertebrates such as mites, slugs, and snails appeared to be less affected by the different management strategies. Ground beetles, spiders, harvestmen, earwigs, and centipedes are all probable predators of lepidopteran and homopteran pests of apple.

Herbicidal control of spotted knapweed, Centaurea maculosa Lamarck, is rarely cost-effective, and sustainable control may require an integrated approach. Cyphocleonus achates (Fahraeus) is a flightless root-feeding weevil of Eurasian origin that has been introduced into North America for biological control of spotted knapweed. We hypothesized that reducing the density of spotted knapweed using reduced rates of picloram would improve the establishment of C. achates. At two sites in western Montana, three adult weevil densities (none, three, and six weevils m⁻²) were released in the fall (1995 at site 1 and 1996 at site 2) in 2-m² plots encircled with enclosures to prevent weevil escape. Six picloram rates (0, 0.03, 0.06, 0.09, 0.12 or 0.15 kg ha⁻¹) were applied the following spring before weevil emergence in a randomized complete-block design with four replications (18 treatments per replication). Spotted knapweed density and spotted knapweed and grass cover were sampled in July each year following treatment. Weevil numbers were counted annually in August. By 1998, picloram rates of >0.09 kg ha⁻¹ had reduced spotted knapweed density from ≈500 to ≈175 plants m⁻². Cover was reduced from ≈60 to10% at these rates. There was no detectable impact of weevils on spotted knapweed. Weevil numbers in plots treated with picloram >0.09 kg ha⁻¹ were about half (0.5 weevils per plot) the numbers found in the other picloram treatments (1.25 weevils per plot). Weevil numbers in plots treated with 0.03, 0.06, and 0.09 kg ha⁻¹ were similar to the unsprayed control. Weevil numbers were highest when spotted knapweed cover was between 30 and 70%. Results show than reduced rates of picloram do not limit weevil establishment.

The effect of native and recently introduced natural enemies of the cassava mealybug Phenacoccus herreni Cox & Williams in northeastern Brazil is reported in this article. Studies of population fluctuation of the mealybug and its natural enemies were conducted between 1994 and 1997 in three cassava fields located in Muritiba, Itaberaba, and São Gonçalo, State of Bahia. At least ≈85% of the parasitoids found in those fields were composed of the recently introduced species Apoanagyrus (=Epidinocarsis) diversicornis (Howard), Aenasius vexans (Kerrich), and Acerophagus coccois Smith. A. diversicornis was found in all fields during most of the experimental period, whereas A. coccois and A. vexans were only found in the fields where they had been released. A. diversicornis out-competed A. vexans in São Gonçalo, but not A. coccois in Itaberaba. Most predators collected belonged to the genera Hyperaspis, Nephus, and Diomus, all of the family Coccinelidae. The results of this work suggest that the concerted action of the three introduced parasitoids and the native natural enemies was sufficiently efficient to control P. herreni at low levels, in the fields where the study was conducted.

Diuraphis noxia (Mordvilko) is an exotic, economically important pest in North American cereal crops. A survey of insect natural enemies of D. noxia was made from 1991 to 1994 on a farm using organic farming methods. Crested wheatgrass, Agropyron cristatum L., had fewer D. noxia and natural enemies than barley, Hordeum vulgare L., or wheat, Triticum aestivum L., but on all plants D. noxia was the most abundant aphid. We observed 41 species of natural enemies: 15 carabids, 12 coccinellids, six spiders, five syrphids, two nabids, and two chrysopids. The most consistently abundant were the coccinellids and nabids. Hippodamia convergens (Guerin) and Nabis alternatus Parsh were the most common species in each family, respectively. Diaeretiella rapae M’Intosh was the only primary parasitoid found in the 4-yr study, and D. noxia parasitism rates were generally <5%. Four hyperparasitoids, found in association with D. rapae, combined to make a 29% average hyperparasitism rate. Predator and parasitoid exclusion studies using cages showed aphid populations to be between 2.6 and 11.2 times higher in cages compared with wheat plants exposed to natural enemies. Four predatory species were released—Eupeodes nuda (F.), Hippodamia variegata (Goeze), Leucopis ninae Tanasijtshuk, and Propylea quatuordecimpunctata (L.). Of these, only a small colony of eight L. ninae and only one P. quatuordecimpunctata were later observed. Four parasitoids species were released—Aphelinus asychis Walker, Aphelinus varipes Forester, Aphelinus matricariae Haliday, and Diaerietilla rapae. Only A. asychis and D. rapae were observed after the release date, although D. rapae were already present.

In March 1994, Gonipterus scutellatus Gyllenhal, an Australian weevil that feeds on foliage of eucalypts, was discovered in Ventura County, CA. By the time of its discovery, the weevil was defoliating eucalypt trees in citrus orchard windrows. We imported, reared, and released a parasitoid of the weevil’s eggs, Anaphes nitens Siscaro (Hymenoptera: Mymaridae). A. nitens was firmly established in several southern California counties by mid-1997 and was spreading in tandem with its host. The wasp has proven to be effective in suppressing weevil populations, killing >95% of weevil eggs, except possibly in areas where insecticides are applied to manage pests of field crops. A. nitens appears to be a promising biological control agent for G. scutellatus in California.

Natural enemies have not been shown previously to play a significant role in regulating thrips in field crops. Most thrips are r-selected with population attributes that are believed to result in thrips outstripping the capacity of natural enemies to regulate thrips populations. In replicated field experiments conducted in 1995, insecticide applications to peppers were observed to increase rather than decrease populations of Frankliniella spp. thrips in flowers. We conducted experiments in 1996 and 1997 to determine if this phenomenon resulted from exclusion of predators. Species of thrips abundant in the pepper flowers were Frankliniella occidentalis (Pergande), F. tritici (Fitch), and F. bispinosa (Morgan). The only common predator in the flowers was Orius insidiosus (Say). Different treatments of biological and synthetic insecticides were used which altered the population densities of prey and predator. Covariate analyses over time were used each year to separate insecticide and predator effects on thrips populations. The predator significantly suppressed populations of all three thrips species. F. occidentalis and F. tritici reproduced in pepper flowers, but most of the larval thrips in untreated plots were F. occidentalis. Near extinction of F. occidentalis adults and larvae occurred within days after predator:prey ratios reached 1:40. Exclusion of the predator with synthetic insecticides resulted in continued abundance of thrips. We conclude that O. insidious was an effective predator that suppressed populations of Frankliniella spp. in field peppers during a period when thrips were rapidly colonizing and developing in the flowers. Species of Orius are abundant predators nearly worldwide, and the role of density dependence in regulation of thrips populations should be reevaluated.

Promoting generalist predators in agriculture via habitat manipulation has gained much interest in biocontrol research. Straw shelters have been used by Chinese farmers for >2,000 yr to provide temporary spider refugia during cyclic farming disturbances. This method, however, has not been systematically investigated on larger scales in western-style agriculture. Our preliminary observations indicated a significant decrease in the abundance of spiders (76%) and their egg sacs (75%), after conventional tillage of soybeans [Glycine max (L.) Merr.]. We hypothesized that providing alternative habitats in tilled fields could conserve predatory assemblages following this major disturbance. We used modular habitat refugia constructed of chicken wire loosely filled with bedding straw to provide temporary habitats for epigeic predators in a soybean field. Refugia held 5–36 times the spider density compared with open field, and the production of spider egg sacs was enhanced 18–87 times. Almost 60% more spider species were found in refugia than in open field. Abundance of harvestmen, carabids, and staphylinid beetles also significantly increased in habitat refugia. Increased habitat cover and provision of alternative prey in habitat refugia may have caused this dramatic predator increase. Soybean seedlings grown within 1 m of habitat refugia suffered 33% less insect damage compared with plants at control locations. Decrease in seedling damage, however, did not significantly increase soybean seed production. Applications of discrete habitat refugia may provide an alternative to habitat manipulation techniques to conserve and augment arthropod predators in agroecosystems.

Effects of Beauveria bassiana (Balsamo) Vuillemin infection on feeding and ovipositional behavior of Lygus hesperus Knight were investigated in the laboratory. In the feeding experiment, bugs were inoculated with different concentrations (LC₁₀, LC₅₀, LC₉₀) of B. bassiana conidia and feeding damage was measured on flower buds of Wisconsin fast plants, Brassica rapa L., after 5 d. We detected greater feeding damage by inoculated bugs compared with noninoculated bugs, particularly bugs that died during the experiment. In the oviposition experiment, bugs were inoculated with a high concentration of conidia (LC₉₀ at 25°C) and incubated for 6 d at 25 or 35°C, temperatures that are optimal and suboptimal, respectively, for B. bassiana growth. Most inoculated bugs died at 25°C but survived at 35°C during the 6-d experiment. Incubation temperature did not significantly affect L. hesperus oviposition. B. bassiana inoculation reduced the oviposition rate of lygus bug, particularly in bugs that did not show sporulation at the end of the experiment. If B. bassiana is used for lygus bug control in seed crop fields, the behavioral changes of infected bugs are unlikely to contribute to a reduction in seed damage.