Two field experiments were conducted in 1995–1996 to determine if there are common photosynthetic and vegetative growth responses among genotypes of maize, Zea mays L., to larval western corn rootworm, Diabrotica virgifera virgifera LeConte injury. Specific variables measured from rootworm infested and noninfested plants were midday leaf photosynthetic rate, plant growth stage, and plant height during 9–18 leaf growth stages. Three yellow-dent hybrids, five white food-grade dent hybrids, and a popcorn hybrid were included in the study. Results suggest that there may be a common negative photosynthetic response within maize to larval injury during vegetative growth stages. Transient reductions in photosynthetic rate occurred in rootworm infested maize at both low to moderate levels of root injury, which after a lag period, led to significant reductions in plant height. This trend was consistent across hybrids in both experiments during each year. Plant growth stage was not significantly affected by rootworm injury during vegetative periods.

Beet armyworm, Spodoptera exigua (Hübner), is a freeze-susceptible and migratory species, but can overwinter in temperate areas without diapause. Most developmental stages reared under constant environments are able to induce a cold-hardening process in response to a brief exposure to cool temperature. In this study, we analyzed the effect of daily temperature and photoperiod cycles on the cold-hardening process. Rearing temperatures significantly affected cold tolerance of larvae. In constant temperature regimes, as rearing temperature decreased, cold tolerance increased. Cyclic temperature regimes caused a significantly higher cold tolerance than did constant temperatures with the same daily average. In cyclic regimes with three combinations of a thermophase temperature and three different cryophase temperatures below a developmental threshold (13°C), cryophase temperature had a significant effect on cold tolerance. Cold-hardening induced by rearing temperatures was associated with decreases of supercooling points and increases of hemolymph osmolalities and glycerol contents. A cyclic photoperiod produced a higher cold tolerance than did constant dark or light. There was, however, no variation in cold tolerance among different cyclic daylength regimes. These results indicate that fluctuating temperature and photoperiod significantly affected cold tolerance of S. exigua.

The objective of this study was to find one or more rearing methods that would allow us to release Osmia lignaria Say populations from natal nests to pollinate February-flowering almonds, Prunus amygdalus Batsch, in California’s Central Valley. We exposed three phenologically distinct O. lignaria populations (early-, mid-, and late-flying) to different temperature treatments through development and wintering for a total of nine rearing treatments. These treatments combined three approaches to obtain early bee emergence: (1) exposing bees to warmer or fluctuating temperatures, or both, during development; (2) exposing bees to warmer wintering temperatures; and (3) using early-flying bee populations from Central Valley California latitudes. Extended periods of high prewintering temperatures resulted in apparent fat body consumption of prewintering adults and reductions in springtime adult longevity. In general, temperature treatments that promoted rapid immature development, and thus longer wintering periods, resulted in earlier spring emergence patterns of bees well timed with bloom period of almonds. Warmer wintering periods also resulted in earlier emergence. In addition to providing good bee-bloom synchrony, several treatments also yielded vigorous emerging populations, rapid establishment and nesting, and population increases. The potential importance of our results to anticipated increases in the demand for pollination services in California’s Central Valley almonds is discussed.

We assessed lepidopteran communities in replicated stands representing two hardwood forest ecosystems in northern Michigan during a 3-yr period that coincided with the first gypsy moth outbreaks experienced by this area. Adult Lepidoptera were collected at 4-wk intervals each summer in 1993–1995 in eight forest stands. Four stands were classified as ecological landtype phase (ELTP) 20, and they were dominated by oaks (Quercus spp.), a favored host of gypsy moth, Lymantria dispar (L.). The other four stands were classified as ELTP 45, and they were dominated by northern hardwood species with few preferred hosts of gypsy moth. Gypsy moth populations and defoliation fluctuated dramatically in ELTP 20 stands during the 3 yr, reaching outbreak levels in at least one year in all four stands. In ELTP 45 stands, gypsy moth populations and defoliation were minimal. More than 12,000 adult Lepidoptera representing 453 taxa were collected from the eight stands. Lepidopteran species composition differed significantly between ELTPs for species collected in early season months (May and June), but not for late season months (July and August). Within ELTP 45 stands, abundance and species richness of Lepidoptera were not affected by differences between years, stands, or the interaction of the two factors. In ELTP 20 stands, the interaction of stand and year affected overall lepidopteran abundance and diversity of late season species. Species composition of late season lepidopteran communities in ELTP 20 stands may have been affected by gypsy moth population fluctuations, although patterns were not consistent in all years. A subset of oak-feeding species appeared to be negatively affected during outbreak years, but other native Lepidoptera appeared to be resilient, perhaps reflecting the spatially and temporally limited duration of gypsy moth outbreaks.

In central Brazil, recolonization of burned cerrado areas by leaf-miners on Roupala montana (Aublet) and Tabebuia ochracea (Chamisso) and leaf-gallers on Andira humilis (Martius) begins 6–7 wk after burning, and is simultaneous with the sprouting of new shoots of the insects’ host plants. The most abundant R. montana leaf-miner used mostly young red leaves, whereas the others were only seen on green expanding leaves. The recolonization of burned areas was mainly exogenous, although some life-cycle adapted species lived through the fire and recolonized endogenously. The gallers from A. humilis and miners from T. ochracea also showed distributions that resulted from exogenous recolonization. Availability of young leaves may be driving the dispersal of one Tineoidea leaf-miner, because these prefer to oviposit on very young nonexpanded R. montana leaves. Adaptations of leaf-miners and gallers to survive a fire may include pupating >2–3 cm below ground or feeding on leaves above the scorch height. Delayed recolonization 1 km away from the borders of the burned area suggests that large burnings may cause a loss of diversity and that the time for recovery of a burned area is dependent on the dispersal capacity of the organisms.

Using alfalfa grown for seed, we tested the hypothesis that seed set for a fixed number of pollinations is lower when the standing crop of open flowers is high than when it is low. This could occur if pollinators are more likely to move between flowers on the same plant, causing self-pollination, when flowers are abundant. The hypothesis has practical implications for agricultural production because self-pollinations produce fewer seeds per pod than do cross-pollinations in alfalfa. We simulated seed set in a model that included published movement patterns of the alfalfa leafcutting bee, Megachile rotundata (F.) (Hymenoptera: Megachilidae), and estimates of seed set when a series of flowers on the same plant are hand pollinated. Seed set from a fixed number of pollinations averaged only ≈6–7% higher when standing crop was low than when standing crop was high. This small increase in seed set would be difficult to detect experimentally because of high variability between plants. M. rotundata appears to move with a 56% probability of leaving a given raceme and a given plant; this foraging behavior results in few flowers visited per plant. A pollinator with a higher probability of leaving racemes and plants could set slightly more seed than M. rotundata, whereas a pollinator with a lower probability of leaving racemes and plants would be more affected by flower standing crop than is M. rotundata. The distribution of flowers visited per raceme by bees in alfalfa can be predicted by superimposing the movement probability on the distribution of open flowers per raceme. This conceptualization of bee movement on flowers differs from (but is not mutually exclusive of) resource-driven optimal foraging models, and is useful for predicting geitonogamy.

The relationship between azalea lace bug, Stephanitis pyrioides (Scott), abundance and components of vegetational texture were examined in managed landscapes to determine which component(s) best explained patterns in lace abundance. In managed landscapes, azalea lace bug is a key pest of azaleas and its abundance varies dramatically in time and space. The components of vegetational texture examined were light exposure, plant species diversity, evenness and richness, host patch size, and structural complexity of the landscape. The best habitat predictors of lace bug abundance were structural complexity and light exposure explaining 54 and 53% of lace bug variation, respectively. Three of the remaining four components also were significantly related to lace bug abundance. Further examination of light exposure revealed that afternoon readings explained more of the variation (52%) in lace bug abundance than morning readings (9%). Of the five vegetational strata that comprise structural complexity, the overstory tree layer and ground cover/turf layer (76%) were the best predictors of lace bug abundance. The implications of this work are that landscapes can be evaluated for susceptibility to lace bugs and perhaps other pests. It also provides information for designing landscapes that support fewer pest problems, resulting in low-input sustainable landscapes.

Effect of mating status on locomotor activity was examined in females of the parasitoid wasp Nasonia vitripennis (Walker). Mated females were more active than virgin females in both strains of N. vitripennis that were tested and regardless of whether or not the mated female stayed with her mate before testing. Mated females were more active than virgin females when tested immediately after mating and when tested 1 h, 1.5 h, and 2 h after mating. Mated females were still more active than virgin females when both had been allowed to parasitize a host for 2 h. Mated females were not significantly more active than virgin females at 1, 3, and 5 d after mating. Mated females that were allowed to parasitize a host for 3 h before testing were less active compared with those not given a host. Amount of activity was independent of a female’s head width and did not affect a female’s subsequent offspring production. Despite being more active, mated females did not kill more hosts than virgin females. However, among mated females, females that were more active subsequently killed more hosts, whereas this was not true for virgin females. Discussion of relevance to biological control and suggestions for future research are provided.

Developmental times and mortality were determined for four stages of greedy scale Hemiberlesia rapax (Comstock), a key pest of kiwifruit, Actinidia deliciosa (A. Chevalier) C. F. Liang et A. R. Ferguson variety deliciosa, in New Zealand. Scale were reared on potato tubers at seven constant temperatures and developmental stage and mortality were assessed at regular intervals. This required the removal of the scale cover to enable stage and mortality to be accurately determined. High numbers of scale (>1,400) were required at each temperature to sustain a frequent destructive sampling regime. Scale survival to the reproductive stage ranged from 0% at <12.3°C to 45% at 24.6°C. The time for 50% of the live scale population to reach each developmental stage was determined using a Bayesian smoothing program. A linear model of scale development was developed for each stage based on a single, temperature-independent distribution of normalized developmental time. A linear regression of development rate against temperature was used to estimate developmental thresholds that were 9.6, 9.7, 10.3, and 10.6°C and it took 257, 552, 882, and 992 degree-days (DD) to reach the second, third instar, mature, and first reproductive stages, respectively.

The movement of polygynous Solenopsis invicta Buren queens from hot environment to a cooler environment was influenced by the queen’s dominance ranking within the colony. This study used a split nest design in which the temperature could be controlled independently in either of the two nest areas that were joined by a sealable plastic tube. Before the study, three queens were marked and ranked by worker preference from a small fire ant colony and introduced into one of these nest areas. After they were acclimatized to the nest, the colony was induced to move by changing the nest temperature. When subjected to increasing heat, the colony left the nest and moved to a cooler location. The results showed that the alpha (most preferred) queen had an advantage over the beta and gamma queens when exposed to hot conditions because the workers demonstrated a definite pattern of behavior of selectively moving the queens from the hot nest to the cooler alternate nest. The behavior of the workers and the queens during the colony’s movement was observed and time to reach safety for each queen was recorded. The workers appeared to have a significant control over the queen’s movement. If the queens were separated from each other and had only one choice of a route to safety, the least dominant (gamma) queen arrived at the new nest location first, because there were fewer workers to interfere with her movement. When the queens were together, the dominant queen arrived at the alternate nest first; dominant queens workers interfered with the movement of the subordinates. However, given a choice between a favorable and harsher nest, the least dominant queen chose equally between the two; whereas, the dominant queen had little choice, her workers chose the favorable nest. We repeated the experiment by subjecting the colony to cold conditions. When the nest was cooled the workers aggregated around each queen and became inactive.

Wild-type and recombinant nucleopolyhedroviruses (NPVs) were compared with respect to their potential for environmental transport by the predatory spined soldier bug Podisus maculiventris (Say), the scavenging fly Sarcophaga bullata (Parker), and the house cricket Acheta domesticus (L.). Viruses tested were variants of Autographa californica (Speyer) NPV (AcNPV): wild-type virus (AcNPV.WT), AcNPV expressing a scorpion toxin (AcNPV.AaIT), and AcNPV expressing a mutated juvenile hormone esterase (AcJHE.SG). All three insects ingested Trichoplusia ni (Hübner) larvae infected with or killed by each of the three NPVs. The type of virus that killed T. ni larvae did not affect feeding preference of the cricket or fly. The cumulative survival curves for the three nontarget insects did not depend on whether they ingested AcNPV.WT-infected, recombinant-infected, or uninfected T. ni. Thus, direct effects of the recombinant viruses on nontarget organisms probably are similar to those by wild-type NPV. Within 5 d after ingesting virus-infected larvae, all three nontarget insects voided >1,000 times the median lethal dose of each NPV against neonatal Heliothis virescens (F.). All three insects defecated significantly more AcJHE.SG virus than the other viruses. Thus, AcNPV.AaIT and AcJHE.SG potentially can be transported away from a release site by the predator and the two scavengers and thereby contact additional nontarget species.

We studied larval dispersal behavior of two rice stem borers, Scirpophaga incertulas (Walker) and Chilo suppressalis (Walker), to evaluate the potential of seed mixtures for resistance management in B. thuringiensis (Bt) rice. Both species showed extensive movement among plants (or “hills”) in plots of transplanted rice, during the course of larval development. On rice plants at the vegetative stage, almost all S. incertulas larvae dispersed on the day of eclosion. On plants at booting stage, most S. incertulas bored into hills on which egg masses were placed (referred to as the “release hill”). Almost all neonate C. suppressalis also bored into the release hill, at both vegetative and booting stages. At both rice growth stages, most larvae of both species dispersed to new hills between 7 and 18 d after eclosion. Both S. incertulas and C. suppressalis moved among tillers within the release hill, as indicated by an increase in dispersion among tillers over time. The distance and direction of dispersal of ballooning S. incertulas larvae was influenced by wind speed and direction. Larval recovery within plots generally declined rapidly over the first 5 d after egg hatch and then more slowly thereafter. Because many S. incertulas and C. suppressalis larvae move among tillers within hills and among hills within plots, many larvae in plots planted to seed mixtures will consume tissue from both Bt and non-Bt plants. This behavior will reduce the cumulative dose of toxin ingested and can accelerate the evolution of resistance.

Sowing seed mixtures of transgenic and nontransgenic plants is one approach to establishing refuges for resistance management of crops transformed with Bacillus thuringiensis (Bt) toxins. We studied larval dispersal and survival of two rice stem borers, Scirpophaga incertulas (Walker) and Chilo suppressalis (Walker), to evaluate the potential effectiveness of seed mixtures for resistance management of Bt rice, Oryza sativa L. Experiments were conducted with two cry1Ab-transformed rice varieties, ‘IR58’ and ‘Tarom Molaii’, and corresponding nontransgenic controls. During 0–24 and 24–48 h after egg hatch, the proportion of C. suppressalis larvae dispersing from the natal plant did not differ between transgenic and control plants for either rice variety. Dispersal by S. incertulas did not differ between transgenic and control plants of IR58 during either 0–24 or 24–48 h, but a greater proportion of S. incertulas larvae dispersed from transgenic Tarom Molaii than from control plants 24–48 h after eclosion. Larvae that dispersed 0–24 h after eclosion on IR58 and 0–24 and 24–48 h after eclosion on Tarom Molaii were collected and transferred to stem pieces of control plants. No differences in survival were detected between larvae that dispersed from transgenic or control plants 24 (IR58) or 72 h (Tarom Molaii) after dispersal. Because both stem borer species move among plants during larval development, seed mixtures may not be the most effective approach to maintaining refuges for resistance management. However, additional experiments to compare the dispersal and fitness of Bt-resistant and -susceptible stem borer larvae are needed.

To better understand the host range and factors acting on the population structure of native grape phylloxera, Daktulosphaira vitifoliae (Fitch), Vitis species in 22 central and eastern U.S. states were surveyed for grape phylloxera presence and abundance. Data for frequency of attack and mean number of galled leaves per vine were compared among Vitis species and among six geographic regions defined according to topographic, ecological, and heuristic criteria. Four of the seven Vitis species that were identified had been attacked by grape phylloxera and both the frequency of vines that were attacked and the mean number of galled leaves differed among species and regions. In general, V. riparia (Michaux) and V. vulpina (L.) were attacked more frequently than expected and V. cinerea (Englemann) less than expected. The distributions of three of these species, V. vulpina, V. aestivalis (Michaux), and V. cinerea, were largely overlapping, but the distribution of V. riparia was not. It was found, to the near exclusion of other species in the northern United States, in the region formerly occupied by the Laurentide Icesheet. An increasing south to north gradient in phylloxera abundance was observed. Fourteen per cent of the surveyed vines were attacked in the Gulf Coast, 34% in the Central region, and 66 and 64% in the Northcentral and Northeastern regions. The mean number of galled leaves per vine conformed to this trend. In addition, sexual morphs were produced by apterous gallicolae in galls on V. cinerea but not on other Vitis species. This life cycle variant has previously been described only in the southwest United States. These data will be useful for future molecular phylogeographic studies and in the understanding, evaluation, and deployment of phylloxera resistant germplasm.

Plant morphology has been shown to influence the biology of herbivores through changes in oviposition behavior, feeding preferences, and plant tenure times. The goal of the work herein was to establish whether or not differences in plant morphology can affect the performance and distribution of the pea aphid, Acyrthosiphon pisum (Harris), on peas, Pisum sativum L. Fecundity and intrinsic rate of increase were the selected parameters to measure the aphid’s performance. Genetic near-isolines of the garden pea were used to determine the effect of plant morphology on the pea aphid. The use of genetic near-isolines eliminates as much as possible confounding effects, such as phytochemicals, that could occur when comparing different plant species or cultivars. Four plant lines differing in leaf morphology (Normal, af, tl, and aftl) and two lines with normal and reduced stipules (Normal and st) were tested. Changes in plant morphology did not have a significant effect on pea aphid total fecundity or intrinsic rate of increase. Although there were no changes in fecundity caused by plant morphology, longevity was significantly influenced both by leaf type and stipule size. The morphology of the leaf did not affect the within-plant distribution of the pea aphid on three plant lines tested.

Rhagoletis juglandis Cresson is a specialist that deposits its eggs into the husks of developing walnut fruit. Like other walnut infesting flies in the R. suavis group, R. juglandis actively superparasitizes its larval hosts. However, little is known regarding the degree to which hosts are reused and the ecological context under which host reuse occurs. This field study examined the pattern of host utilization by R. juglandis and how fruit variables such as volume and penetrability affect the degree that hosts are reused. Fruit on four of five study trees were synchronously infested and within 2–2.5 wk all fruit on these trees were infested. Fruit on a fifth tree were significantly less penetrable than those found among the other trees in the study and this may explain why fruit on this tree were rarely used throughout the season. Walnut hosts were commonly multiply infested and reuse of hosts occurred in as few as 1–2 d after first infestion. Infestation levels within fruit appeared to stabilize 4–5 d after fruit were first used. Fruit volume was positively correlated with both the number of punctures on hosts and the infestation levels within hosts that had been infested for either 1–2 or 4–9 d. Large fruit were infested more quickly than small fruit, although this trend was stronger on some trees than others. Finally, despite a size-penetrability correlation among two of the five trees, penetrability itself did not explain either which fruit were preferentially used throughout the season or the infestation levels within fruit.

For three species of geometrid moths with noneruptive population dynamics, physiological and behavioral responses of ovipositing females to larval host deprivation were recorded. Single substrate trials were used. Availability of adult food was also varied to manipulate physiological condition of the moths. Egg production rate decreased only weakly in the absence of host plant, whereas it was strongly influenced by adult feeding. The time from the beginning of the experiment to initiation of oviposition was largely determined by presence of suitable host. This variable, oviposition latency, was only weakly affected by nutritional status of the females. Oviposition rates also remained lower on unsuitable hosts after oviposition was initiated. This indicates that the effect of inferior oviposition substrate was not limited to postponing oviposition. Host deprivation and adult feeding both lead to accumulation of chorionated eggs in abdomens. However, high egg loads of the fed females did not alter their behavior in the direction predicted by optimality models. We conclude that oviposition latency was the only variable in which female responses to unsuitable hosts were sufficiently strong to have potential significance for population dynamics. Latency presumably corresponds to dispersing behavior in nature. Such a response, not having been observed in an outbreaking geometrid studied earlier, may reflect a behavioral mechanism capable of stabilizing local population dynamics. The results are discussed in the light of the gradation from capital to income breeding. In herbivorous insects, oviposition latency may serve as an index of overall sensitivity of ovipositing females to adverse environmental conditions.

Intraspecific competition in Tomicus piniperda (L.) was studied in Ascot, United Kingdom, with special emphasis on its effect on progeny adult (i.e., offspring) weight and progeny production. Although the weight of female progeny adults was significantly decreased by increasing attack density (density of colonization), the latter did not significantly affect weight of male progeny adults. Similarly, increasing adult female weight was significantly related to increasing egg gallery length, number of hatched eggs, and final production of progeny adults. This production was also affected by host (tree) species. Females breeding in Pinus sylvestris (L.) showed a higher production of progeny adults than those in Pinus nigra variety maritima (Ait.) Melville. Overall, increasing intraspecific competition appears to contribute to the regulation of T. piniperda populations through reduction of weight and fecundity of female progeny.

The pink bollworm, Pectinophora gossypiella (Saunders), remains a significant pest of cotton (Gossypium spp.) in the southwestern United States, but is not known to be established in the primary cotton production areas of the southeastern United States. Absence of P. gossypiella may be the result of federal regulatory action (e.g., monitoring, quarantine, and eradication), climate, or other ecological factors. The objectives of this study were to determine how low temperatures and high soil moisture common to the southeastern United States might affect mortality of diapausing, preconditioned, and nondiapausing larvae of P. gossypiella. In constant temperature incubators set between 22 and 5°C (0% moisture, 0:24 [L:D] h), nondiapausing prepupal (fourth or fifth instar) larvae died more quickly at lower temperatures. At 5°C, 90% of the cohort was dead after 12 d. Similarly, prepupal larvae that had been reared under diapause inducing conditions (20°C, 10:14 [L:D] h) since neonate stage also died more quickly at lower temperatures. A separate developmental assay indicated that the larvae were not in diapause. In this case, 26 d at 5°C were required to achieve 90% mortality. For diapausing, prepupal larvae collected from the field, mortality was greater at 5°C than at any other temperature tested, but larvae could withstand 5°C for 60 d before 90% of the cohort died. In response to moisture, as soils at 10°C became saturated (>195% gravimetric soil moisture), most diapausing larvae (≈60%) died within the first 10 d of the experiment. These studies suggest that diapausing, late instar larvae of P. gossypiella are more resilient to the effects of low temperature than nondiapausing individuals and are able to tolerate high soil moisture for moderate lengths of time. Temperatures and soil moistures in the southeastern United States are not sufficiently cold or wet to completely preclude establishment of P. gossypiella.

This study investigated aspects of the ecology, pest status, and management of Nezara viridula (L.) in pecans in Australia. N. viridula adults were shown to feed in the pecan canopy from January to March, causing premature nut fall and black pitting of the kernel. N. viridula was shown not to be able to breed in pecans. Population increases of N. viridula occurred on uncultivated hosts (weeds) growing in the orchard understorey and surrounding vegetation, from which adults subsequently invaded the pecan trees. Mowing of understorey weeds was evaluated as a control measure for reducing N. viridula numbers in the orchard without the requirement for pesticide application. The action of natural enemies (parasitoids of eggs) was evaluated. Parasitism of eggs by Trissolcus basalis (Wolllaston) peaked at ≈54% during spring and summer. The results of this study are discussed in relation to the seasonal phenology of N. viridula on weed hosts in eastern Australia and the potential for management of N. viridula in other orchard crops.

The predatory mite Neoseiulus fallacis (Garman) is an important biological control agent of spider mites in many agroecosystems, including ornamental nurseries. In this study, sampling methods, tendencies to overwinter among a range of plant types, and the effect of winter protective practices were assessed for N. fallacis females. Ten spider mite-infested plant species representing a range of five plant types (conifer, shade tree, evergreen shrub, deciduous shrub, herbaceous perennial) were inoculated with 100 adult female N. fallacis in late autumn. Early the following spring, N. fallacis was extracted from each plant species by either washing plant parts (leaves, branches, trunks-crowns) in 70% ethanol and filtering contents or placing plant parts into separate Berlese funnels for 5 d. The washing method extracted more N. fallacis than the funnel method. When comparing overwintering among a range of plant types, higher densities of N. fallacis were extracted from conifers > evergreen shrubs > herbaceous perennials = deciduous shrubs = shade trees. With respect to overwintering location of N. fallacis within plants, higher densities of N. fallacis were recovered on leaves than trunks-crowns; branches were intermediate. Densities of N. fallacis were positively correlated with those of their spider mite prey. Higher densities of N. fallacis were collected from plants that were held in a greenhouse versus those left unprotected or under a sheet of polyethylene plastic. Manipulating overwintering sites for the conservation of phytoseiid natural enemies is discussed.

Mortality of first instars of Pieris brassicae (L.) and Agrotis segetum (Schiffermüller) exposed to crude destruxin extracts per os was analyzed by time-concentration-mortality regressions based on the complementary log-log (CLL) model, and was compared with the mortality from pure destruxins A and E and the synthetic analog hpy-6 destruxin E. The model described the temporal course of mortality for both insects exposed to the different destruxins. Based on estimated LC₅₀ and LT₅₀ values, P. brassicae was much more susceptible to destruxins than A. segetum. Destruxin E seemed to be the most potent against P. brassicae, followed by the synthetic analog hpy-6 destruxin E, and destruxin A was least active. The results of the toxicity of pure destruxins against P. brassicae provide a basis for further investigations on destruxins as control agents against this insect. A. segetum larvae were only weakly susceptible to destruxins and the observed mortality of the larvae seemed to be a result of starvation caused by an antifeedant effect of the destruxins rather than by direct toxicity. Overall, the per os bioassays point toward a potential for possible future use of destruxins as control agent against lepidopteran pest larvae. The results do, however, also document, that the activity level of destruxins depends highly on the target insect species.

Conidial suspensions of Beauveria bassiana (Balsamo) Vuillemin and Paecilomyces fumosoroseus (Wize) Brown & Smith were tested for pathogenicity to third-instar nymphs of Trialeurodes vaporariorum (Westwood) reared on cucumber and tomato plants. Nymphs were highly susceptible to infection by both fungi after a one-time application of conidia onto cucumber plants. In contrast, insects reared on tomato plants were significantly less susceptible to infection. We hypothesized that the glycoalkaloid tomatine might have been involved in antimicrobiosis on tomato leaves. Tomatine mixed with Noble agar at five concentrations was tested for its effects on germination of conidia of both fungi. Germination of conidia of B. bassiana was only slightly affected at the two highest concentrations of tomatine. In contrast, germination of conidia of P. fumosoroseus was completely inhibited at 500 and 1,000 ppm of tomatine. The in vitro tolerance of tomatine by B. bassiana contradicted our in vivo data. Sequestered tomatine by T. vaporariorum nymphs would explain, at least partially, the insect’s defense against the pathogens. That little in vitro inhibition of B. bassiana was found supported the hypothesis that B. bassiana was inhibited only in vivo, after the penetration process. Inhibition of P. fumosoroseus might have occurred on the insect’s cuticle before penetration, as evidenced by the complete inhibition of spore germination in vitro in the presence of tomatine at 500 and 1,000 ppm. An explanation for the differential in vitro sensitivity of B. bassiana and P. fumosoroseus to tomatine is being sought.

Establishing flowering plants in and around fields to provide pollen and nectar resources for natural enemies has shown promise as a strategy to enhance biological control of crop pests. Natural enemies are selective in their flower feeding, however, and show preferences for certain plant species. In this study the relative attractiveness of 11 flowering plant species to aphidophagous hoverflies (Diptera: Syrphidae) was evaluated at the Oregon State University Vegetable Research Farm. Six of these plant species were also evaluated at two other farm sites. Of the 12 species of hoverflies collected, Meliscaeva cinctella (Zetterstedt), Toxomerus marginatus (Say), Toxomerus occidentalis (Curran), Sphaerophoria sulfuripes (Thomson), and Scaeva pyrastri (L.) were common to all three sites. Attractiveness of flowering plants to foraging hoverflies was assessed by conducting timed observations of feeding-visit frequencies. Flowering periods varied between plant species and comparisons were made only for plant species flowering on a particular date. Relative attractiveness of plant species to hoverflies differed between dates and sites. Among early-season flowering species, coriander, Coriandrum sativum (L.), was fed from most frequently. Among late-season flowers, yarrow, Achillea millefolium (L.), fennel, Foeniculum vulgare (Miller), and Korean licorice mint, Agastache rugosa (Fischer & C. A. Meyer) were fed from most frequently. These results help in the selection of plants to enhance biological control, but final selection of plants for this purpose requires considering flower, natural enemy, and pest phenologies, and pollen and nectar quality and availability.

Thermoregulatory behavior was studied in two key acridid pest species from west and south Africa. Locustana pardalina Walker (Orthoptera: Acrididae) from the arid Karoo region of South Africa was an active behavioral thermoregulator using postural adjustments and microhabitat selection to elevate and then maintain body temperatures at a preferred level between 38 and 41°C for much of the day. Both cool weather and time of season significantly affected the ability of these locusts to reach and maintain these preferred temperatures. Hieroglyphus daganensis Krauss (Orthoptera: Acrididae) from the humid tropical river valleys of west Africa was not an active behavioral thermoregulator and showed none of the postures or habitat selection associated with such behavior. Body temperatures varied little across the day being generally around 32°C. The humid, wet habitat where this species occurs and the uniformity of the thermal environment appeared to preclude the development of elaborate thermal behaviors seen in L. pardalina and other behaviorally thermoregulating ectotherms. The implications of host thermal behavior and the marked difference both within and between species under different environmental conditions are discussed in terms of biological control using a biopesticide based on an entomopathogenic fungus. It is concluded that the fundamental importance of host body temperature in relation to the fitness of the insect and its ability to cope with disease challenge, although generally overlooked in biocontrol programs, has significant implications for the successful development of microbial pest control.

The effect of light on survival of entomopathogens is well described and efforts are underway to develop formulations that may protect an entomopathogen from damage by sunlight. The availability of solar simulators allows for year-round testing of solar protectants. A commercial formulation of Bacillus thuringiensis Berliner and an unformulated baculovirus isolated from Anagrapha falcifera (Kirby) were exposed to various amounts of light from a solar simulator or the sun to determine the relative effect of each source on loss of insecticidal activity. Rate of pathogen degradation was essentially the same for both light sources when original activity remaining was regressed against total energy (as measured by joules/m²). The amount of time required to reduce activity was different, however, because of a difference in total energies produced by the solar simulator and natural sunlight. Virus was approximately two times more sensitive to light than bacteria. To obtain 50% reduction of virus activity, exposure to 1.8 × 10⁷ joules was required, whereas 3.2 × 10⁷ joules was necessary to achieve a similar loss of activity for B. thuringiensis. The importance of reporting energy levels from various solar simulators is discussed.

The mirid bugs Dicyphus tamaninii Wagner and Macrolophus caliginosus Wagner and the anthocorid bugs Orius majusculus (Reuter) and O. laevigatus (Fieber) are abundant generalist predators in unsprayed vegetable crops of the Spanish Mediterranean coast. We evaluated the functional response of these predators to greenhouse whitefly pupae and western flower thrips larvae (second instar) on cucumber leaf disks in the laboratory. Parameters of the random-predator equation obtained were compared among all predator–prey combinations to determine the potential role of the predators in the biological control of both pests in cucumber. D. tamaninii was efficient at consuming whitefly pupae at high and low densities and thrips at high densities, and took less time to handle either of these prey than did the other predators. Anthocorid bugs were efficient at consuming thrips at low and high densities, but did not performed well as predators of whiteflies. M. caliginosus was less efficient when consuming whiteflies but performed better when preying on thrips. It is concluded that D. tamaninii may have a good action in the control of both greenhouse whitefly and western flower thrips, whereas M. caliginosus and both Orius species may be slower in controlling whitefly and be similarly efficient in consuming western flower thrips.

The Diaprepes root weevil Diaprepes abbreviatus (L.) is a major pest of citrus, ornamentals, and vegetables in Florida and the Caribbean. Entomopathogenic nematodes can provide substantial control of the root feeding larvae, but their efficacy can be affected by soil type. Our objective was to determine the effects of three soil types on the control of D. abbreviatus with Steinernema riobrave (Cabanillas Poinar & Raulston) and Heterorhabditis bacteriophora Poinar. In the laboratory we measured nematode virulence and persistence in a Marl, Ridge (entisol), and Flatwoods (spodosol) soil. The Marl soil contains a high silt and clay content (80 and 15%, respectively), whereas the other soils are >93% sand and typical soils of citrus production in Florida. The virulence of S. riobrave was greater than H. bacteriophora in all soils. Both nematode species exhibited greater virulence and persistence in Marl soil compared with sandy soils. Nematode virulence was greater in the spodosol than in the entisol soil. Oxygen levels (in the cups) were not significantly different among the soils. Further research is required to determine the cause of these trends and the applicability of these findings under different water tensions and under field conditions.

By promoting adult longevity, carbohydrate food sources can influence the effectiveness of parasitoids in biological control of insect pests. Adults of Bathyplectes curculionis (Thomson), a parasitoid of the alfalfa weevil (Gyllenhal)(Coleoptera: Curculionidae), benefit greatly from continual nourishment: field-collected adults lived significantly longer when provided sugar-water than those provided water only. Access to one potential source of adult nutrition in the field, dandelion flowers, enabled laboratory-reared wasps to live only slightly but nevertheless significantly longer than those that had access to water only, foliage of alfalfa, or flowers of Phacelia tanacetifolia Bentham. The wasps were observed foraging readily on dandelion but could not insert their heads into and did not pierce florets to obtain nectar. For each of the foods provided (dandelion, phacelia, alfalfa, or water alone), virgin females lived significantly longer than mated females. This was not the case, however, when wasps were provided a honey-water solution; both virgin and mated females lived more than 20 d on average. These results suggest that even in the absence of oviposition, female longevity is reduced by the simple act of mating when inferior but not superior foods are available. The striking contrast in longevity of wasps provided honey versus other carbohydrate foods raises the question of how much female wasps in nature realize their potential lifespan and fecundity. Dandelions and pea aphid honeydew appear to be the most likely sources of carbohydrates for the wasp in alfalfa fields. Supplemental foods such as floral plantings may promote realization of such potential longevity, but the quality and accessibility of floral foods for the wasp will need to be evaluated carefully.