To assess their ability to modify cuticular hydrocarbon (CHC) composition and survive adverse conditions, Cryptotermes brevis (Walker) nymphs were subjected to various combinations of temperature and relative humidity. Cuticular hydrocarbon profiles of C. brevis were consistent with previous studies. Alkenes were the most prevalent in the CHC mixture, comprising 54.5% of the total hydrocarbon ( n = 12), whereas n-alkanes and branched alkanes comprised 24.8 and 6.3%, respectively. Sixteen compounds yielded >2% of the total hydrocarbon and were subsequently tested for temperature and humidity effects in two successive experiments. In both experiments, temperature effects were found: n-C29 increased and n-C25 decreased with increasing temperature. Similarly, five compounds ( n-C25, n-C27, n-C29, C39:2, and C41:2) were analyzed for relative humidity effects in experiment 2, based on the results of experiment 1; only C41:2 indicated a significant positive relative humidity effect. The remaining 11 compounds comprising >2% of the total hydrocarbon were tested, and a single statistically significant increase was found with C45:3 with increasing temperature. Significant positive effects were found with total alkenes, dienes, and trienes; relative humidity had the opposite effect on total n-alkanes. In both experiments warm, damp conditions were detrimental to survival. Overall, CHC modification was minor; and given that C. brevis has numerous adaptations for dealing with desiccation and an inability to tolerate high relative humidity it suggests that this species may not vary widely from a highly desiccation-tolerant state.

Levels of phenolic glycosides and protein influence the quality of aspen leaves to herbivorous insects, and vary in relation to genetic and environmental factors. This research was conducted to assess the independent and interactive effects of phenolic glycosides and protein on the performance and detoxication enzyme activities of gypsy moths, Lymantria dispar (L.), and forest tent caterpillars, Malacosoma disstria Hübner. We fed fourth-stadium larvae aspen leaves supplemented with 0, 2, or 4% (wet weight) phenolic glycosides and 0 or 5% (wet weight) casein. We measured stadium duration, growth and consumption rates, and food conversion efficiencies. In addition, we measured the activities of three midgut enzymes likely involved in the metabolism of phenolic glycosides: β-glucosidase, esterase, and glutathione transferase. Phenolic glycosides reduced performance of both insect species in terms of increased developmental time and decreased growth rates. Casein supplementation increased growth rates of gypsy moth larvae but slightly reduced growth rates of forest tent caterpillars. Phenolic glycosides and protein did not interactively influence stadium duration or growth rates. β-glucosidase activities declined for both insect species when reared on diets with phenolic glycosides. Esterase activities were induced by phenolic glycosides only in gypsy moths, whereas glutathione transferase activities were induced by phenolic glycosides in both species. Casein supplementation had little influence on enzyme activities, and phenolic glycosides and protein interactively affected only forest tent caterpillar esterase activity.

Two groups of 50 heifers were given a subcutaneous injection of either abamectin (Avomec) or doramectin (Dectomax) at a dose rate of 200 μg/kg live weight. A third group of 50 heifers remained untreated. Dung samples were collected on 1, 3, 6, 9, 18, 24, 34, and 42 d after injection, and excreted residues were bioassayed using the dung beetle Onthophagus binodis Thunberg. Fewer newly emerged adults of O. binodis survived exposure to dung from cattle treated 3 and 6 d previously with abamectin or 9 d previously with doramectin than from dung of untreated cattle. Both compounds induced a range of sublethal effects on O.binodis. Abamectin residues excreted in dung up to 42 d after injection had a deleterious impact on ovarian condition, brood mass (egg) production, and larval survival. Doramectin residues only had a deleterious effect on these parameters at 3 and 6 d after injection relative to dung from control cattle. Analysis of the dung collected at each date after injection indicated that moisture content, pH, and percent nitrogen were not different from other physicochemical profiles conducted on cattle dung. Doramectin residues attained maximal concentrations of 101.1 μg/kg 3 d after injection followed by a linear decline with an elimination half-life estimate of 15 d. The bioassay data indicated that doramectin concentrations of <60 μg/kg have minimal impact on the mortality and reproductive potential of O. binodis and that deleterious effects to this species will be evident for only 1–2 wk after administration of the drug to cattle. The potential ecotoxic effects of these compounds are discussed in terms of dung beetle activity and strategies for parasite control of cattle in the Australian environment.

Oviposition and diapause behavior were compared among populations of Colorado potato beetle, Leptinotarsa decemlineata (Say), from six locations in 1994 and 1995. Locations ranged from Winnipeg, Manitoba (49° 49′ N), to Rosemount in east central Minnesota (44° 44′ N). Newly emerged first summer generation adults were held in field cages at each location for 7–14 d, then observed for 7 d in the laboratory for frequency of oviposition and frequency of burrowing behavior associated with diapause. Females from the Red River Valley seldom oviposited and although frequency of burrowing varied among locations it was independent of field and laboratory conditions. Under long-day laboratory conditions, 9–15% of females from east central Minnesota oviposited with frequency dependent on photoperiod experienced in the field, the critical photoperiod was 15.8 h. Under long-day laboratory conditions, 18–52% of beetles from east central Minnesota burrowed with frequency dependent on cumulative temperatures experienced in the field. Cool conditions were associated with higher frequencies of burrowing. Beetles from Rosemount exhibited identical responses under short-day and long-day laboratory conditions. In contrast, under short-day conditions, beetles from Big Lake did not oviposit and frequency of burrowing was not dependent on field conditions. We concluded that there is local geographic variation in Colorado potato beetle populations not only between the Red River Valley and east central Minnesota, but also among the different locations within these two areas.

The fruit of the osage orange tree, Maclura pomifera (Raf.) Schneid (Moraceae), has long been thought to be repellent to insects. A preliminary study reported here confirmed repellency of fruit extracts to the maize weevil, Sitophilus zeamais Motschulsky. Two isoflavones, osajin and pomiferin, were isolated from the mature fruit of M. pomifera in high purity (≥95%). Testing of purified osajin and pomiferin failed to show repellency. Repellency is likely caused by factors other than isoflavones in the fruit.

Studies were conducted to identify host location cues used by Roptrocerus xylophagorum (Ratzeburg), a larval/pupal parasitoid of bark beetles. In Y-tube olfactometer bioassays, female R. xylophagorum were attracted to infested bark (i.e., phloem, cambium, and outer corky bark tissues) removed from bolts of loblolly pine, Pinus taeda L., colonized by the late instar larvae and pupae of the bark beetle Ips grandicollis Eichhoff (Coleoptera: Scolytidae). In contrast, bark taken from recently cut, uninfested bolts interrupted attraction to infested bark when these were presented together. Larval and pupal hosts isolated from infested bark were not attractive to parasitoids, whereas frass removed from the larval mines in infested bark was highly attractive. Bark from which hosts or both hosts and host frass were removed remained highly attractive. Bark sandwiches (fresh bark with the exposed surface pressed to glass microscope slides) infested with either third-instar or adult female I. grandicollis were attractive to female parasitoids, whereas bark sandwiches with only mechanical damage to the phloem tissue were unattractive. A steam distillate of bark infested with host larvae was attractive to female R. xylophagorum, whereas a distillate of fresh pine resin was not attractive. Volatiles from the experimental baits were collected on Porapak Q and analyzed by coupled gas chromatography-mass spectrometry. Several compounds were identified that distinguished baits with biological activity. These data show the importance of the complete host/plant complex for attraction of R. xylophagorum to its host’s habitat and suggest a possible role for particular odors from uninfested host plant tissue in directing foraging parasitoids away from locations with few or no hosts.

A major advance in sterile insect release programs against tephritid fruit fly pests has been the development of genetic sexing strains, which allow the production of males-only lines for field release. Genetic sexing strains both reduce the costs associated with mass rearing and enhance the mating effectiveness of sterile males. Research and application of genetic sexing strains has been limited largely to the Mediterranean fruit fly. However, translocation-based genetic sexing strains based on pupal color mutants have been constructed in the oriental fruit fly, Bactrocera dorsalis (Hendel). Here, we describe the results of laboratory tests on B. dorsalis that compared the relative success of males from a translocation-based sexing strain and wild males in mating competition for wild females. Additional tests examined the effect of irradiation and exposure to methyl eugenol on the mating frequency of males from the genetic sexing strain.

Fifty seven species representing 26 genera of Carabidae and 46 species representing 14 genera of Elateridae were trapped in flight above a potato dominated agricultural landscape. The estimate of species richness for Carabidae and Elateridae for this habitat was increased 2.2 and 4.6 times by the use of impact traps distributed vertically at 10 different levels. Both families were captured up to 14.3 m. This confirms the widespread use of flight by ground and click beetles although it seems infrequent in most species. The slope of the regression of flight occurrence against height averaged −0.923 and −0.988 for Carabidae and Elateridae, respectively. However, specific vertical flight profiles within the Elateridae vary considerably ranging between −1.665 and −0.092. This indicates that most species actively control their vertical flight profile flying either close to the vegetation or randomly through the air column tested. Implications for insect monitoring are discussed. The temporal distribution of flight was similar for the two families with early peak frequency for host plant location and oviposition.

We assessed habitat differences in ground-dwelling spider communities that stem from fine-scale differences in plant cover types and height in a shortgrass steppe ecosystem. The number of spiders captured in pitfall traps was used to determine habitat and temporal dynamics in the spider communities. Two habitat types were sampled, grass and mixed-grass/shrub during May, June, July, and August 1995 and 1996. Spiders in the Lycosidae (56%) and Gnaphosidae (29%) were the numerically dominant spiders collected. The Lycosidae was represented by three species and significantly more abundant in grass habitats in 1995 only. The Gnaphosidae was the most speciose family collected (15 spp). The most abundant species of Gnaphosidae exhibited consistent habitat and seasonal patterns of species turnover and abundance during the 2-yr study. Results from detrended correspondence analysis revealed significant species-specific differences in the spider communities between the two habitats. Of the 10 most abundant species, Schizocosa mccooki (Montgomery), S. mimula (Gertsch), Gnaphosa clara (Keyserling), and G. brumalis (Thorell), were more abundant in grass sites. The most abundant spiders in the mixed-grass/shrub habitat were Schizocosa spp. (immatures), Gnaphosa spp. (immatures ), G. sericata (Koch), Haplodrassus signifer (Koch), Habronattus altanus (Chamberlin), and Xysticus nigromaculatus (Keyserling). Overall, the spider communities differed between grass and mixed-grass/shrub habitats in their response to seasonal change, and these differences in community composition were similar both years of the study. Our results underscore the importance of habitat selection at fine-scales and patterns of seasonal activity that translate to population and community patterns at larger spatial and temporal scales.

Cannibalism, a widespread phenomenon in nature, can both reduce competitors and introduce a high-quality food into the cannibal’s diet. We investigated the dietary benefits of cannibalism for larvae of the multicolored Asian lady beetle, Harmonia axyridis (Pallas). Cannibalism might benefit the larvae by allowing cannibals to take advantage of prey-detoxification already completed by the victim or the different, and perhaps more diverse, feeding history of the victim. In two laboratory experiments we reared H. axyridis larvae with aphid prey, and with or without conspecifics to consume, and recorded larval development and survivorship. In the first experiment, we fed groups of H. axyridis larvae an aphid species of intermediate quality, Aphis nerii (Boyer deFonscolombe), and prevented or permitted consumption of conspecifics of varied quality—conspecific victims had either fed upon the same intermediate quality food as the focal individual or had fed upon a high quality food. Cannibalism increased survivorship and shortened development time, and eating conspecifics that had fed upon higher-quality food further shortened early development. In a second experiment, we reared groups of H. axyridis larvae with one or both of two aphid species of poor ( Uroleucon spp.) or intermediate [ Aphis fabae (Scopoli)] quality, and either permitted or prevented cannibalism. Larvae could complete development when fed both conspecifics and the intermediate quality aphid, but not on any other diet. Overall, when mixed with other foods, cannibalism allowed H. axyridis larvae to develop on prey that were otherwise nutrient deficient or toxic.

The objective of this work was to study the effect of winter low temperatures on survival, reproduction, and growth of immature stages, and the host fruit infestation ability of the Mediterranean fruit fly, Ceratitis Capitata (Wiedemann), wild population in the southernmost part of Greece. Adult flies were monitored using Jackson and McPhail traps from November to May over a period of 3 yr. In January–March, absolute minimum and maximum air temperatures were 1–4.5 and 19–26°C, respectively, whereas the average monthly minima and maxima were 6.2–9.7°C and 15.4–18.5°C, respectively. Adults were found at every inspection period (every second week) in at least one of the trapping systems used or the years of the study. Until the beginning of April developed eggs and sperm were found in >70% of females trapped. From mid-April until mid-May, 20–70% of females were fecund and fertile. This increased at the end of May– beginning of June to high percentages, >80%. Females survived in cages in the field an average of 4 mo in winter–spring, with some females surviving 5–6 mo. Infested ‘Navel’, ‘Valencia’ oranges, or bitter oranges could be found throughout the experimental period in all 3 yr and live eggs were always detected in infested fruits. Grown larvae were found in relatively high percentages of infested fruits until March, especially in bitter oranges, which appear to be a preferred host (up to 25 pupae per infested fruit). In April–May, grown larvae were seldom detected. In winter, larval development from the time of fruit sampling until larval exit often took 1.5–2 mo. The duration of the pupal stage under field temperatures was ≈2 mo for those pupae formed between December and February. This was reduced progressively to 10–20 d for those pupae formed in May. The mortality of young larvae (still near the oviposition hole) was between 40 and 70% from November until May, whereas adult emergence from pupae kept in the field fluctuated between 20 and 80%. In conclusion, under the conditions of southern Greece (Heraklion, Crete) the Mediterranean fruit fly continues reproduction and growth during the cooler part of the year but at reduced rates and with longer duration of larval and pupal stages. This must be considered in control or eradication applications.

Effects of timing of overwintering larval-cocoon formation, constant temperature, and soil moisture on postdiapause development of Carposina sasakii Matsumura were examined. Also, a forecasting model of its spring emergence was constructed based on degree-days. The development time from overwintering larva to adult emergence was not significantly different among soil moistures in the range of 10–20%, but it was different according to the timing of larval-cocoon formation in the previous year. The weight of cocoons containing an overwintering larva was less for cocoons formed after 6 October than cocoons formed before 15 September. There was a positive correlation ( r = 0.47) between the overwintering larval-cocoon weight and its development time to adult. Approximately 3–4% of C. sasakii showed a prolonged diapause spending 2 yr as larval-cocoons in the soil. A greater proportion (18.4%) of heavier cocoons (>0.040 g) remained in diapause in the current year compared with normal weighed cocoons (0.022–0.040 g) (1.6%) or lighter cocoons (<0.022 g) (0%). The adult spring emergence showed a two-peak emergence pattern in which the first major peak occurred in late June and the second smaller peak in late July. A bimodal distribution model was developed to describe this emergence pattern. The bimodal model predicted more accurately C. sasakii spring emergence times than the Weibull model.

Densities of Callirhytis cornigera (Osten Sacken), a cynipid with alternating agamic and sexual generations that develop in woody stem galls and blister-like leaf galls, respectively, often vary among neighboring pin oaks, Quercus palustris Muenchhausen. We studied the ovipositional behavior of agamic wasps and tested several hypotheses to explain intraspecific variation in susceptibility to leaf gall induction. Agamic females laid eggs primarily into green-tip buds. Heavily galled trees had proportionately more vulnerable buds than lightly galled trees during peak oviposition in 1998, supporting the phenological synchrony hypothesis, but not in 1999. Contrary to plant vigor hypothesis predictions, rates of shoot or leaf expansion were similar for lightly and heavily galled trees. Agamic wasps were transferred from heavily infested trees onto shoots of heavily or lightly infested novel trees, or back onto their natal trees, to test for inherent differences in susceptibility to leaf galling. Leaf gall induction was greater on natal than novel trees in 1997, supporting the demic adaptation hypothesis, and there was a trend for greater leaf gall induction on heavily galled than lightly galled novel trees. These patterns, however, did not reoccur in 1998. Although synchrony of emergence with budburst is critical to ovipositional success of agamic C. cornigera, other host-related factors, including those affecting stem gall induction or survival of the agamic generation, probably are more important in determining variation in tree infestation levels. Once a suitable host is colonized, limited wasp dispersal may also contribute to buildup of insular populations on particular trees.

The backpropagation algorithm in artificial neural networks was used to forecast dynamic data of a forest pest population of the pine needle gall midge, Thecodiplosis japonensis Uchida et Inouye, a serious pest in pine trees in northeast Asia. Data for changes in population density were sequentially given as input, whereas densities of subsequent samplings were provided as matching target data for training of the network. Convergence was reached, generally after 20,000 iterations with learning coefficients of 0.5–0.8. When new input data were given to the trained network, recognition was possible and population density at the subsequent sampling time could be predicted.

The spatial distribution of Mussidia nigrivenella Ragonot was studied in maize fields and on four major wild host plants in the Republic of Benin, West Africa. Maize ears were sampled at harvest in 1994 and 1995, and fruits of the wild host plants were collected monthly from January 1996 to December 1997 during the fruiting periods of the respective host species. The spatial distribution was analyzed using the variance-to-mean ratio (s²/m), an index of departure from Poisson distribution, Iwao’s patchiness regression, and Taylor’s power law. The variance-to-mean ratio and the index of departure from Poisson gave similar results of nonrandom distribution of M. nigrivenella populations on the different host plants out of Gardenia sokotensis Hutch (Rubiaceae). On this specific host plant, the variance-to-mean ratio was not different from 1, whereas there was no overlap of the observed population and the Poisson distribution. Iwao’s patchiness regression was inappropriate for our data as shown by the nonhomogeneity of variance, whereas Taylor’s power law fitted the data well. Based on Taylor’s power law, M. nigrivenella was aggregated on all host plants out of G. sokotensis. The degree of aggregation of M. nigrivenella was positively correlated with the fruit size of the host plants. The optimal number of secondary sampling units needed to estimate M. nigrivenella densities on the respective host plants in Benin, varied from four fruits on G. sokotensis to 10 pods on P. biglobosa. These values were used to calculate the time expenditure needed to sample maize fields or wild host plant trees to achieve a predefined precision level of 25%.

Oviposition rates of the European corn borer, Ostrinia nubilalis (Hübner), were examined on corn plants from the 3-leaf through postharvest growth stages during 1994–1996. Per-plant rates in the field during vegetative stages showed a gradual increase as new leaves appeared, and a sharp increase when reproductive plant parts emerged. Laboratory studies indicated a similar relationship between oviposition rate and plant growth stage: significantly greater rates occurred on reproductive plants. Laboratory experiments showed that when only 4-leaf to early green tassel (preanthesis) plants were present (simulating conditions during early-season European corn borer activity), per-plant oviposition was significantly greater on the oldest (11-leaf to green tassel) plants. When the oviposition rate was based on leaf area rather than on a per-plant basis, however, statistical differences between vegetative stages were lost. When European corn borer females were given only reproductive plant stages (simulating conditions during late-season European corn borer oviposition), plants in the green tassel, anthesis, green silk, and brown silk stages had generally equal oviposition rates, and these were significantly greater than on postharvest plants. This European corn borer oviposition simulation, when based on leaf area, showed the same pattern as the per-plant oviposition. Thus, leaf area appears to influence oviposition during the vegetative stages, when leaf area is rapidly expanding, but is of little influence after tassels emerge and leaf area is expanding at a slower rate or declining. Moth alighting in the laboratory indicate a behavioral difference between sexes. Females alighted on plants identical to those favored for oviposition. In contrast, males showed no preference for any growth stage of corn.

A computer model for simulating population dynamics of Lyctocoris campestris (F.), a predator of stored-product insects, was developed using data from the literature and newly collected data for adult longevity and fecundity. Immature development time and survival, adult longevity, fecundity, and cannibalism were simulated. The model was validated at ambient environmental conditions during three seasons in Wisconsin. The model accurately simulated development of the predator feeding on larvae of the Indianmeal moth, Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), in the validation studies. The model will be useful in optimizing mass-rearing and augmentative releases of this predator for biological control of stored-product insect pests.

We assessed the effect of plant patch shape and surrounding vegetation on the density, emigration, and immigration of predatory coccinellids, and on the density of their aphid prey Brevicoryne brassicae (L.). Between spring 1997 and fall 1999, we set up square and I-shaped patches of Brassica oleracea Plenck surrounded by Medicago sativa L. or Allium porrum L. Medicago sativa is frequently used by coccinellids, whereas A. porrum is not. We used a factorial (2 × 2) randomized block design, and evaluated the density of coccinellids and aphids every 10 d. We also evaluated emigration and immigration of adult coccinellids through mark-recapture experiments. We quantified the population increase of aphids, and the final live mass of plants. All insects were more abundant in patches surrounded by A. porrum than in those surrounded by M. sativa, and coccinellids were occasionally more dense in square patches than in I-shaped ones. Coccinellids emigrated less from square patches, either surrounded by A. porrum or M. sativa, and immigrated more to patches surrounded by A. porrum. Aphids showed a higher population increase, and plants of B. oleracea ended up being heavier in patches surrounded by A. porrum, particularly in I-shaped patches. Surrounding vegetation and plant patch shape seem to have a direct effect on the density of coccinellids by modifying their immigration and emigration patterns, but also seem to have an indirect effect by changing plant growth and its effect on herbivore recruitment.

Phytoseiid mites associated with hazelnut in Sicily were sampled during 1991–1993. Two orchards at two different altitudes (500 and 1,000 m above sea level) were taken into account. No chemicals had been applied in the two fields for at least 7 yr and the agricultural practices were limited (spring tillage and removal of dead branches). Thirteen species, out of a total of 19, were collected at the lower altitude and 14 at the higher; eight of these species [ Kampimodromus aberrans (Oudemans), Typhlodromus intercalaris Livshitz & Kuznetsov, Amblydromella crypta (Athias-Henriot), Typhlodromus rhenanoides Athias-Henriot, Amblyseius andersoni (Chant), Euseius stipulatus (Athias-Henriot), Paraseiulus erevanicus Wainstein & Arutunjan, Phytoseius finitimus Ribaga sensu Denmark] were common to both fields. As far as the distribution of phytoseiids was concerned, we took into consideration their presence on three different sites of the plants: trunk, low branches, and high branches. On the whole the population of phytoseiid mites was uniformly distributed on the plant from October through April, although as far as the single species were concerned, some were uniformly distributed on the plant and some showed a preference toward a particular part of the plant. K. aberrans showed a preference toward high and low branches at 1,000 m above sea level (asl), whereas T. intercalaris showed such a preference in both sites. However, at 500 m asl, A. crypta preferred the trunk, whereas T. rhenanoides was uniformely distributed on the plant in both sites.

Plant compensation may be specific to the defoliation of a particular insect herbivore, or a generalized response to herbivory. These alternate hypotheses were tested by measuring biomass and seed production of Brassica napus L. and Sinapis alba L. in response to 0, 25, or 75% defoliation of seedling plants. The herbivores were adults of Phyllotreta cruciferae (Goeze), larvae of Plutella xylostella L., and larvae of Mamestra configurata (Walker). Although defoliated to the same extent, both B. napus and S. alba compensated most for defoliation by M. configurata and least for defoliation by P. cruciferae. Both plant species compensated better for 25% than for 75% defoliation, and S. alba compensated better than B. napus. Laboratory and field experiments showed similar patterns of compensatory leaf growth, but recovery was more rapid in a controlled environment. Compensation was associated with changes in root biomass that were correlated with foliage biomass, indicating that root-shoot ratios were maintained. Complete recovery of foliage after defoliation did not assure complete recovery of plant fitness. For these three herbivorous insects, compensation by two plant species for defoliation was specific to the insect defoliator, and not a generalized response to herbivory. The compensatory responses of the two plant species explain, in part, the differential impact the three herbivores have on the crops.

Gypsy moth females that survived inoculation with Lymantria dispar (L.) nucleopolyhedrovirus (LdNPV) as fifth instars were smaller as pupae and laid fewer eggs as adults. Treatment with both wild type virus containing the egt gene and a genetically manipulated, egt- virus, lacking this gene, reduced pupal mass to a similar degree. Sublethal infection with wild type virus reduced the masses of surviving pupae at 20, 25, and 28°C. A relationship between virus dose (5,000, 50,000 and 500,000 occlusion bodies per larva), mass of pupae, and egg mass size only occurred in one experiment in which larvae were reared at 25°C and inoculated 5 d after molt to the fifth instar. Vertical transmission of overt infection occurred in two of 13 egg masses (15%) produced by females inoculated with virus as larvae. The five larvae infected with virus were ≈0.5% of the larvae tested. Whether sublethal effects of LdNPV infection occur in field populations of gypsy moth remains to be tested.

The specificity of compensation by Brassica napus L. and Sinapis alba L. was investigated for herbivory by three biting and chewing herbivores: a small adult Coleoptera and a small and a large Lepidoptera larva. Phyllotreta cruciferae (Goeze) damaged the apical meristem and its defoliation of cotyledons was highly dispersed; the defoliation of Plutella xylostella L. was moderately dispersed over cotyledons; and Mamestra configurata (Walker) defoliated large contiguous areas of cotyledons. These types of herbivory were simulated in the field, and postdefoliation compensation by the plants was quantified: leaf length, relative growth rate of foliage, and seed production were measured. Plants were unable to compensate completely for meristem defoliation combined with highly dispersed cotyledon defoliation, and compensated better as cotyledon defoliation became less dispersed. Because compensatory responses to artificial defoliation were similar to and usually indistinguishable from those of insect herbivory, we conclude that the specificity of compensation is caused by the type of defoliation. Other interaction-specific processes such as transfer of growth-affecting chemicals from insect to plant need not be invoked. Sinapis alba compensated for defoliation better than B. napus because of inherent differences in compensatory responses, not because insects defoliate the two plant species differently.

The pea aphid, Acyrthosiphon pisum (Harris), attacks a wide range of legumes including many important forage and vegetable crops. Although economic injury levels for pea aphids are seldom exceeded in forage crops, aphid densities can reach extremely high levels during a single harvest cycle. After harvest of forage crops, large numbers of pea aphids may disperse into proximate vegetable fields. The objective of this study was to determine the potential impact of immigrating pea aphids on vegetable crops adjoining forage crops in the agricultural landscape. Pea aphids collected from alfalfa and clover were evaluated for their ability to survive on and their propensity to feed on vegetable crops. The survival of pea aphids collected from clover and alfalfa was significantly higher on these forage crops than on peas, green beans and lima beans in laboratory transplant experiments. In additional laboratory experiments, alfalfa-adapted aphids produced significantly fewer aphid offspring on lima beans than on alfalfa, and the adults and offspring had significantly higher mortality on lima bean leaves than on alfalfa leaves. Analysis of aphid feeding with an electronic monitor confirmed that alfalfa-adapted pea aphids feed on phloem sap from alfalfa but never feed on lima beans. These results led us to predict that pea aphids immigrating from alfalfa and other forage crops during harvest would not establish persistent, damage-causing populations in nearby vegetable crops. Our field data on pea aphid populations in lima beans were consistent with this hypothesis. High densities of pea aphids were found in lima beans immediately after harvests of nearby alfalfa fields, but high aphid densities did not persist >3 d. Our study suggests that although aphids can emigrate from forage crops to vegetable crops at densities above published action thresholds, the amount of damage actually caused by these forage-crop adapted aphids in higher-value vegetable crops will be minimal. It may be unnecessary to treat aphids in lima beans and other vegetables when aphids have immigrated from harvested forage crops. These findings suggest that pest management decision-making in vegetables can be improved by considering the source of immigrating pests such as pea aphids.

To clarify the relationship between overwintering and spring migration in the bollworm Helicoverpa armigera (Hübner) in Israel, we caged larvae under field conditions in fall and used sex pheromone traps to monitor field populations the following spring. No diapause was detected in October-exposed individuals. Overall, 67.7 and 89.2% of the individuals exposed to field conditions during November and December, respectively entered pupal diapause. Most nondiapausing individuals eclosed early in the following January. In contrast, postdiapause adults started to eclose synchronously in late April. Approximately 50% of the postdiapaused females eclosed before 6 May, 9 d before 50% of the males did. Capture of field H. armigera moths in sex pheromone traps occurred 1 mo before the eclosion of adults from caged overwintering diapause pupae. Moths trapped before the eclosion of diapausing individuals had lower wing loading, fewer wing scales, and larger relative thorax size (ratio of thorax to head widths). These morphometric data imply that the early season field moths were trapped after long distance flight. Taken together, the phenological and morphometrical data support the notion that H. armigera exhibits an early-spring migratory behavior in Israel. These results are discussed within the context of physiological and genetic data from related studies.

The alfalfa weevil, Hypera postica (Gyllenhal), is a major pest of alfalfa in Virginia despite being under complete biological control in the northeastern states. In 1997 we initiated a 2-yr study of alfalfa weevil populations at three different geographic regions of Virginia to better understand the ecological mechanisms underlying the differences in pest pressure among the major alfalfa-growing regions of the state. Alfalfa weevil populations from the low-lying Piedmont plateau, Shenandoah Valley, and southwestern mountain-valley regions were sampled regularly from November until first harvest in each season. Fields located in the Piedmont had significantly higher alfalfa weevil numbers than those in the Shenandoah Valley and southwestern region. Warmer winter temperatures in the Piedmont contributed to a much higher rate of alfalfa weevil oviposition and concomitant higher infestations of larvae in the spring compared with the higher elevations. Parasitization of adult weevils by Microctonus aethiopoides (Loan), which plays a key role in reducing alfalfa weevil reproduction in the northeastern states, was low in all regions of Virginia, particularly the Piedmont. Mortality of alfalfa weevil larvae was comparable to that reported in more northerly states. The dominant natural enemy of weevil larvae was the parasitoid, Bathyplectes anurus (Thomson), which parasitized 36–92% of larvae. Analysis of alfalfa weevil life tables showed that different mortality factors were important in explaining variations in total alfalfa weevil mortality.

Pine needle scale, Chionaspis pinifoliae (Fitch), is a pest of many species of conifers in urban habitats and Christmas tree farms. We found that the scale was abundant in impoverished habitats, such as ornamental landscapes, and scarce in more natural, park-like habitats. Rates of parasitism were highest in impoverished habitats, suggesting that parasitoids were not effective in suppressing scale populations. Generalist predators, however, were more diverse and abundant in natural habitats and appear to be more effective in controlling scales in structurally complex plant communities. Total densities of arthropods and densities of plant-feeding species were greatest in impoverished habitats, suggesting that populations were poorly regulated. Outbreaks of pine needle scale in ornamental landscapes and Christmas tree farms may be discouraged by increasing plant structural and species diversity to favor natural enemies.

The effect of aerial application of Bacillus thuringiensis variety kurstaki Berliner ( Btk) on mortality of gypsy moth larvae caused by the entomopathogens Entomophaga maimaiga Humber, Shimazu, & Soper, and the gypsy moth nucleopolyhedrosis virus ( LdNPV) was evaluated. Three sites in 1997 and four sites in 1998 were established in a randomized complete block design. Larvae were collected weekly to determine the proportion infected with E. maimaiga and LdNPV. In 1997, epizootics of E. maimaiga in control plots boosted infection rates (61%) to levels twice that in Btk-treated plots (33%). Postseason egg mass density and defoliation did not differ between treatments, indicating population reduction early in the season by Btk or late in the season by E. maimaiga was equivalent. Few larvae became infected with LdNPV in 1997, probably because of the relatively low densities of gypsy moth larvae. In 1998, E. maimaiga was again more active in control plots than in Btk-treated plots, but dry weather conditions suppressed activity of E. maimaiga in all plots compared with 1997. LdNPV was also more active in control plots than in Btk-treated plots. On the peak infection date, infection levels in control plots (26%) were sixfold higher than in Btk-treated plots (4%). Despite greater LdNPV activity in control plots in 1998, aerial application of Btk was much more effective than natural LdNPV in suppressing gypsy moth populations. Final egg mass counts were 89% lower in Btk-treated plots compared with control plots. E. maimaiga and LdNPV disease prevalence increased with increases in larval density. Early spring inoculum levels and weather conditions were similar for all plots. Therefore, reduced infection levels in Btk-treated plots were most likely the result of a slower rate of spread of E. maimaiga and LdNPV among larvae in these plots where the larval density was reduced 5- to 10-fold from Btk. When E. maimaiga is active, as observed in 1997, low density populations of gypsy moth may be held in check by E. maimaiga as well as by Btk applications. However, unusually dry conditions, like we observed in 1998, may suppress E. maimaiga activity and allow gypsy moth populations to build.