Assays with a captive Vespula germanica (F.) colony indicated that foragers were more strongly attracted to pear aged 24 h than to 0- or 48-h-aged pear. Sixteen chemicals found in 24-h pear and other foods were tested for their attractiveness to social wasps in a series of four trapping trials in rural and urban settings in Wisconsin. Workers of V. germanica, V. maculifrons, Dolichovespula maculata (L.), and Polistes fuscatus (F.) were most strongly attracted to isobutanol with 0.5% acetic acid added to the drowning solution, confirming previous work. We report for the first time that males of V. maculifrons were trapped in significant numbers by the isobutanol acetic acid combination. None of the tested compounds found in ripe pear was shown to be especially attractive to V. germanica or V. maculifrons workers or males. However, 2-methyl butanol, a compound similar in structure to isobutanol, was found to attract V. germanica and V. maculifrons workers as well as V. maculifrons males. Furthermore, V. vidua (Saussure) differed from the other species in that it was not attracted to the isobutanol acetic acid combination, but was caught in traps baited with 2,4-ethyl decadienoate. This supports earlier evidence suggesting that vespine species are not all alike in their responses to olfactory cues. Our results, taken together with previous work, indicate that some food-borne volatiles may modulate the stimulatory or inhibitory effects of others, suggesting that the search for strong attractants may be furthered by experimenting with combinations of compounds.

Eastern subterranean termite, Reticulitermes flavipes (Kollar), workers were exposed to decreasing temperatures and a shift in photoperiod to simulate conditions that are encountered during the fall in eastern Nebraska. Mean water and fat content in termites exposed to a decreasing thermophotoperiod did not differ significantly from controls or laboratory colony termites. Survival was higher for termites subjected to a decreasing thermophotoperiod than for controls. This could be attributed to acclimation to low temperatures or a delayed mortality due to lowered metabolic activity at low temperature. Previously reported data on soil temperatures taken in Lincoln, NE, at a depth of 91.4 cm showed that the temperature rarely went below 0°C. Our results, observations from previous reports of R. flavipes found at depths >100 cm during the winter, and previously determined lower lethal temperatures and supercooling points suggest that successfully overwintering R. flavipes colonies retreat to soil depths where freezing temperatures are not encountered.

Patterns of feeding by Japanese beetles, Popillia japonica Newman, were studied in relation to time of day or night and to ambient temperature (T_a). We also measured beetles’ thoracic temperatures (T_th) at rest, during preflight warm up, and during flight, and observed their within-plant distributions in relation to sunlight or shade to gain insight regarding whether their in-field behavior involves physiological and behavioral thermoregulation. Finally, we studied startle response as affected by T_a and time of morning. Japanese beetles fed most extensively within trees from midmorning until late afternoon, but also substantially in evening (1800–2200 hours) and sparingly throughout the night so long as T_a was >15°C. Beetles in the field were capable of endothermy, maintaining elevated T_th independent of basking. At low to moderate T_a (19–32°C), nonflying beetles in shade or direct sunlight had T_th as much as 3.75 or 5.5°C higher, respectively, than T_a. Thoracic temperature was elevated during flight, ranging from 32 to 34°C when T_a was 26–29°C. The minimum T_th for take-off flight was ≈27°C. Despite their reputation as sun-loving insects, a high proportion of Japanese beetles was found in shaded microsites (i.e., shade patches, abaxial leaf surfaces), regardless of time of day. The proportion of beetles in sunlight tended to be highest in morning, although that pattern was more evident in soybeans than in linden trees. As T_a warmed from dawn through late morning, the beetles’ response to disturbance changed from falling at T_a <23°C, to about equal numbers falling or flying at 25°C, to all flying at >25°C. Implications of these findings for management of P. japonica are discussed.

Evolutionary and ecological factors were used to assess the likelihood that low winter temperatures limit the range of Diatraea grandiosella Dyar (southwestern corn borer) in the east central United States. In controlled low-temperature mortality trials, dry diapausing laboratory-reared larvae were exposed for 2 d to constant temperatures, ranging from −6.9 to −10.0°C. Mortality of larvae originating from Indiana at the northern range edge was not significantly different from mortality of larvae from Mississippi, over 500 km to the south. However, larvae from these populations had significantly lower mortality than did those from Arizona, suggesting that selection for increased cold-hardiness may have occurred early in the species’ northeastward invasion of the central United States. Temperatures inside intact maize root crowns, the overwintering location of D. grandiosella, were measured over three winters in fields near the species’ northern range edge. Although air temperatures fell below −19°C for up to five consecutive days, root crown temperatures only approached −8°C for periods of a few hours, due primarily to an underappreciated mitigating effect of freezing soil water. Because larvae originating from the east central United States had >60% survival when exposed to −8.8°C for 2 d in the laboratory trials, mortality at the range edge caused by low temperatures was unlikely to have been severe for dry larvae during the three winters during which temperatures were measured. These results suggest that in most years, low winter temperatures are probably not the most important limiting factor at the species’ northern range edge in the east central United States.

We tested the hypothesis that changes in photoperiod alone are responsible for the delay in the onset of sexual maturity that has been previously observed in natural populations of the migratory black cutworm, Agrotis ipsilon (Hufnagel), moth.We hypothesized that under short days, which occur at the onset of the spring and fall migrations, the first age at which males and females engage in sexual communication would be later than under long days typical of nonmigratory periods. Individuals were kept at 25°C from egg to adult under three photoregimes that they encounter in nature at different latitudes: 12:12 (L:D) h (late March and late September), 14:10 (L:D) h, and 16:8 (L:D) h. As predicted, the mean age at which females first called (i. e., released pheromone) was earlier under long-day than under short-day photoregimes, but this trend was not significant. The percentage of females that called over a 6-d-period was similar among photoregimes but it varied with age. There was no interaction between photoperiod and age on the percentage of females calling. Pheromone production, measured as the quantity of Z7–12:Ac in pheromone gland extracts, was lower under long-day than under short-day photoregimes. On average, 1-d-old females produced less pheromone than older females. Photoperiod and age showed a significant interaction in their effect on the quantity of Z7–12:Ac, but not in the direction predicted by our hypothesis. Males reared under short days showed higher percentages of response than did males reared under long days. Age had a significant effect on male response but it was independent from the effect of photoperiod. We conclude that although photoperiod length can influence calling, pheromone production, and male response, it has little effect on the age at which A. ipsilon reach sexual maturity. Changes in photoperiod alone cannot explain the delayed maturity observed in the field. Other factors, alone or in combination with photoperiod, may be necessary to induce the reproductive diapause that A. ipsilon undergoes in its fall migration.

Arthropod and nematode population densities in ‘Tifway’ bermudagrass were studied in field plots to determine the impact of long-term treatments with an organophosphate insecticide (chlorpyrifos), entomopathogenic nematodes [Heterorhabditis bacteriophora Poinar (Heterorhabditidae), Steinernema carpocapsae (Weiser), S. riobravis (Cabanilas, Poinar & Raulston) (Steinernematidae)], and an entomopathogenic fungus [Beauveria bassiana (Balsamo) Vuillemin (Deuteromycotina: Hypomycetes)] applied alone and in combinations. Fifty-five arthropod families or suborders were recorded during a 2-yr period. Staphylinidae, Sminthuridae, Isotomidae, and Oribatida were the four most abundant species groups, accounting for 97.0% of the arthropods collected. Three orders of nematodes and a miscellaneous nematode category also were encountered. Tylenchida was the most abundant nematode species group, accounting for 77.2% of the nematodes collected. Populations of Lycosidae and Staphylinidae were not significantly different from the control in any treatment. However, chlorpyrifos reduced Lycosidae counts in comparison to H. bacteriophora, S. carpocapsae, and H. bacteriophora B. bassiana. Chlorpyrifos also lowered Staphylinidae counts in comparison to B. bassiana, S. carpocapsae, and S. riobravis. Miscellaneous Araneae, Formicidae, and Scelionidae were less abundant in the chlorpyrifos treated plots than they were in any others. By contrast, Sminthuridae densities were highest in the chlorpyrifos plots and were unaffected by any other treatment. In general, chlorpyrifos diminished the abundances of each of the following categories of arthropods compared with all other treatments: plant-inhabiting predators parasitoids, soil herbivores, thatch detritivores, and soil predators. By comparison, soil detritivores were as common in the chlorpyrifos treatment as they were in the B. bassiana, S. carpocapsae, H. bacteriophora B. bassiana, and S. riobravis B. bassiana treatments and were more abundant there than in the H. bacteriophora, S. riobravis, S carpocapsae B. bassiana, and untreated control treatments. In general, fungus nematode treatments showed no evidence of synergism and chlorpyrifos had a stronger negative impact on nontarget arthropod densities than did the microbial treatments.

Effects of vegetational diversity upon abundance of potato leafhopper, Empoasca fabae (Harris), were examined in four agroecosystems. One of the four cropping systems was a soybean monoculture; the other three were relay intercropping systems that varied in the amount of wheat, Triticum aestivum L. (a nonhost plant), planted between soybean rows. Each employed the same planting density and dispersion of a potato leafhopper host plant, soybean, Glycine max (L.) Merrill. The cropping systems formed a gradient of vegetational diversity of host/nonhost plant density. Soybean and wheat were co-present in experimental plots early in the season; following the wheat harvest, all four cropping systems were soybean monocultures. Preceding the wheat harvest, potato leafhoppers were substantially and significantly more abundant in the monoculture than in any of the intercropping systems. Leafhopper densities were extremely low in all the intercropping systems. After the wheat harvest, differences between the monoculture and intercropping systems gradually decreased, and fewer collection dates showed significant differences. Females and males had similar population dynamics and differences among cropping systems. No significant differences in abundance were found among the intercropping systems. Results suggest that the use of host/nonhost intercropping systems would provide growers with an alternative management tactic against potato leafhoppers.

The Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins, causes considerable mortality in Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, forests. Within-stand distribution of mortality was examined in affected stands using geostatistical techniques. A 10 × 10 m grid was established in two 4-ha study sites. Live and beetle-killed host basal area was measured at each node. In a 16-ha stand, a variable-resolution grid was established and the same information collected. The relationship between Douglas-fir basal area and Douglas-fir basal area killed was examined using non-spatially explicit and spatially explicit linear regression models. A positive linear relationship was observed between the variables. Significant spatially explicit models suggest that the relationship is also true at fine scales. Relative variograms were constructed for Douglas-fir basal area before and after the Douglas-fir beetle outbreaks. For the 4-ha sites, increased spatial dependency in the distribution of Douglas-fir basal area was observed as a result of the Douglas-fir beetle outbreak. For the 16-ha site, kriging was used to estimate live Douglas-fir basal area before and after the outbreak to a 10-m resolution and the stand rated for potential mortality illustrating the potential applicability of geostatistical techniques to rating a stand for potential mortality. Cross-validation analysis indicated that although the potential exists for large estimation errors, the majority of the estimates were within acceptable ranges. The study suggests that geostatistical approaches may be suitable to extend our understanding bark beetle ecology and improving the application of extent of mortality models.

Natural habitats surrounding agricultural fields provide a source of natural enemies to assist in pest control. The boundaries among landscape elements filter some organisms attempting to cross them, resulting in differing communities within the landscape elements. Ground beetles are numerous and generally disperse by walking. These qualities make them excellent organisms for the study of boundary dynamics. Our goal was to determine if natural habitats adjacent to wheat fields affected the species composition of ground beetles within the wheat fields. We captured ground beetles from autumn through spring 1996–1997 at two sites using directional pitfall traps placed in wheat fields and adjacent grasslands and riparian zones. Ground beetle abundance reached two peaks, one in autumn and the other in spring. Species composition was most strongly related to these seasons. Axis 1 of a canonical correspondence analysis separated spring active beetles from autumn active beetles. Axis 2 separated winter active beetles. With the effects of season and sites removed, axes 1 and 2 of a partial canonical correspondence analysis separated beetles with respect to habitat. Axis 1 separated beetles into wheat and natural habitat assemblages. Axis 2 further distinguished assemblages in wheat fields as those adjacent to grasslands and those adjacent to riparian habitats. Axis 2 also separated grassland, grassland edge, and riparian edge assemblages from riparian assemblages. Net dispersal of beetles across the boundaries showed no consistent pattern during autumn, winter, or spring. However, mark–recapture studies showed that several species routinely cross boundaries, which resulted in different community structures and an increase in abundance of beetles in the wheat interiors during spring.

Survivorship of experimental cohorts of Mexican bean beetle, Epilachna varivestis Mulsant, was studied in three commercial dry bean (Phaseolus vulgaris L.) fields in 1995 and 1996 near Scottsbluff, NE. Mexican bean beetle survival was relatively low in 1995 but higher in 1996. In 1995, ≈50% of the egg masses did not hatch. The high egg mortality observed was likely related to drought stress of the host plants, because stressed plants turn their leaves over and expose eggs to sunlight. In 1996, environmental conditions were mild compared with 1995, and egg hatch was greater. Mortality of young larvae was lower than it was in the last two larval stages. The cumulative mortality ranged from 92.1 to 95.8% in 1995 and from 60.9 to 75.6% in 1996. No parasitized or diseased larvae were observed in the study fields or in those held for parasitism tests. Larvae from the same cohort (egg mass) were found distributed throughout a maximum range of 3.6 row-meter.

The spatial pattern and probability distribution of Mexican bean beetle, Epilachna varivestis Mulsant, egg masses were studied in four dry bean, Phaseolus vulgaris L., fields near Scottsbluff, NE, during the 1994 and 1995 growing seasons. Sampling was conducted in a regular and uniform grid to guarantee coverage of the field. The experimental unit in all fields was 0.30 row-m, and five measurements were made at 0.76-m intervals. A total of 12,290 locations was sampled. Geostatistics and discrete statistics were used to describe the egg mass distribution. Regression was used to detect and separate macroscale trends from the microscale variation. The presence of macroscale variation indicated a significant edge effect with ovipositing females moving into dry bean fields from their overwintering sites. The microscale variation estimated from the estimated residuals from regressions to estimate trends was studied using semivariograms for all fields. Semivariograms strongly indicate that Mexican bean beetle eggs are randomly distributed across the field and that this random distribution holds across 10-fold differences in population densities. As a result of the significant macroscale trends observed, we conclude that egg mass densities may be greater in areas of the field near edges adjacent to beetle overwintering sites. The probability distribution that best fit the data was the negative binomial. Our results illustrate the importance of scale in discussing and characterizing distribution. Although there is evidence of edge effect at the field level, there is no evidence of spatial dependence between egg samples at the sampling region level. At an even lower level, the egg mass itself, eggs are aggregated.

We investigated the spatial and temporal dispersion patterns of entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) and their host insects in a citrus orchard located in the semiarid region of Israel (the Negev). Spatial patterns of entomopathogenic nematodes were studied in plots differing on their shade level, and at two geographic scales: a macro-scale, which included the entire orchard, and a micro-scale, which investigated the spatial patterns around individual trees. Spatial patterns of insect hosts were only studied at the macro-scale. At the macro-scale, soil samples were obtained from a symmetrical grid in which samples were separated by a distance of ≈20 m; and in the micro-grid, soil samples were separated by a distance of 50 cm. Population levels of entomopathogenic nematodes were spatially autocorrelated using Moran’s I statistics. Population loads of entomopathogenic nematodes, and their spatial and temporal patterns, were not affected by the orchard’s shade level. Entomopathogenic nematode loads were higher during the fall, which coincides with the reported abundance of their main hosts in this region, grubs of Maladera matrida (Argaman). At the investigated scales and distances, we were unable to detect any spatial dependence of entomopathogenic nematode populations or of insect hosts. However, clusters of entomopathogenic nematodes were found to be highly localized in small volumes of soil. At the level of the entire plot area we found a very strong correlation between the number of host insects at a particular time and the level of entomopathogenic nematodes (as indicated by a laboratory bioassay) 1 mo after (shifted-back correlation). We conclude that entomopathogenic nematodes in the Negev orchards have a very low probability of encountering insect hosts, and that under the environmental conditions of the Negev, effective biological control with entomopathogenic nematodes can only be achieved by inundative releases.

Termites (Isoptera) have a strong hierarchical structure due to their social organization. To interpret genetic differences within and among termite populations it is first necessary to create a quantitative scale to determine the meaning of “different.” To accomplish this, the entire hierarchy of genetic similarities in a Hawaiian population of Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae) was defined by multilocus DNA fingerprinting using the oligonucleotide (GTG)₅ as a probe. The genetic background similarity in the population, based on the genetic similarity between unrelated termites, was 0.21 and falls in the range of other natural invertebrate and vertebrate populations. The mean genetic similarity of termites collected from the same collection site was 0.64 (range, 0.58–0.72). This equals an average relatedness of 0.54 within collection sites. The genetic similarity among the offspring of an artificially outbred laboratory colony lies in the same magnitude (0.65). However, genetic similarity within field colonies was significantly lower than the genetic similarity within laboratory colonies derived from pairs of siblings (mean 0.79). This indicates moderate inbreeding within most of the field colonies. This wide range of genetic similarities defines the basis for a detailed description of the population structure as well as the identification of individual colonies of C. formosanus.

Do disturbed habitats along highway rights-of-way encourage the establishment and spread of the red imported fire ant, Solenopsis invicta Buren, in Texas? The objective of this study was to determine if highway rights-of-way harbored S. invicta populations that were significantly different from those in adjacent pastures. Data on S. invicta populations were collected from three transects along highways within S. invicta-infested areas of Texas. One north–south transect, a southern east–west transect, and a northern east–west transect were established in Texas and extended 1,678 km. Twenty-eight sites, ≈80 km apart along transects, were visited between 14 May and 1 June 1996. Numbers of S. invicta mounds, mound vitality ratings, ants collected in bait cups, and vegetative characteristics were measured in rights-of-way and in adjacent pastures at each site. No significant differences in pooled (n = 28) mean numbers or vitality of S. invicta mounds were detected in rights-of-way as compared with those of adjacent properties. However, significantly more S. invicta colonies than expected were found on roadbeds (≤1.0 m from paved surfaces) as compared with the remainders of rights-of-way and to adjacent pastures. Roadbed colonies were also smaller, which suggested that colonies were more recently founded than in the remainders of rights-of-way. Mound population densities and numbers of ants in bait cups were not well correlated with vegetative characteristics measured in this study. In Texas where S. invicta is well established, S. invicta is in a population equilibrium between highway rights-of-way and adjacent pastures. However, highway roadbeds may offer an early successional habitat for S. invicta colonies and may require special survey and pest management attention, especially along the frontiers of infestation in Texas.

Within-plant height (leaf position) of European corn borer, Ostrinia nubilalis (Hübner) egg masses were analyzed in four sweet corn hybrids planted across four planting dates from 1994 to 1996. From the five-leaf to 15-leaf vegetative stages, the mean leaf position of an egg mass was typically at the midpoint of available (nonsenescent) leaves. The mean leaf position of egg masses gradually increased from early to late leaf stages as new leaves were added, and continued to increase during the first reproductive stage (green tassel). The increase in vertical position during vegetative stages was modeled as y = −0.766 0.653(x), where y = nodal leaf position, and x = total leaves expanded (r² = 0.94). However, when the mean egg mass position was expressed as the mean position within available (expanded and nonsenescent) leaves, no relationship was found. These data indicate that during vegetative stages the mean egg mass position increases relative to ground level, but remains near the midpoint of available (nonsenescent) leaves. Mean egg position during the next four reproductive stages (anthesis, green silk, brown silk, and postharvest) stabilized at ear height, or within the immediate two leaf positions above the ear. The distributions of egg masses among leaf positions during the vegetative and reproductive stages generally exhibited normal distributions: where sample sizes were sufficient, 80% (17/21) of the comparisons (having sufficient sample sizes) did not deviate from normality. This study represents the most detailed examination to date on vertical distribution of European corn borer egg masses in corn. Implications of the study in ovipositional ecology and pest management are discussed.

Callirhytis cornigera (Osten Sacken) is a gall wasp that has alternating agamic and sexual generations that develop in large, woody stem galls and small, blister-like leaf galls, respectively, on pin oak, Quercus palustris Muenchhausen. We assessed the spatial distribution of the leaf galls within leaves, shoots, canopy levels, and whole trees, and examined the relationship between leaf gall density and various tree parameters. Within leaves, proportionately more galls were located on primary lateral veins (59.5%) or midveins (38.1%), as compared with the petioles (2.0%) or secondary lateral veins (0.4%). As many as 18 galls occurred on individual leaves, but most leaves contained 0–4 galls. Some current-year shoots contained as many as 132 leaf galls, but most shoots had <20 galls. Leaf gall density did not vary significantly among heights within individual tree canopies, but was highly variable between trees. Leaf gall density at the whole tree level was not related to the tree’s rate of leaf- or shoot expansion. There was no relationship between tree-wide density of leaf galls and overall levels of foliar nitrogen, nonstructural carbohydrates, or protein binding capacity. The leaf galls supported a complex of hymenopteran parasitoids, including Aprostocetus spp., Pentastichus spp. (Eulophidae), Sycophila spp., Eurytoma sp. (Eurytomidae), Brasema sp. (Eupelmidae), and Ormyrus labotus Walker (Ormyridae). Parasitoids and inquilines accounted for nearly 80% mortality of C. cornigera within leaf galls; however, parasitism was only weakly density-dependent, regardless of spatial scale. Implications of these findings for management of C. cornigera are discussed.

We compared the effect of intercropping on oviposition and emigration behavior of two related specialist moth species. The effect of height of the intercrop species (red clover) on oviposition was studied in field cages, using the leek moth, a specialist on Allium species, and the diamondback moth, a specialist on Brassica species. The moths were also evaluated in an open field experiment. Emigration of both moths was studied in the laboratory and in the field in cages with host plants, red clover (nonhost), host plant and red clover, and bare soil. The possible influence of noncontact stimuli was also studied in the laboratory. The leek moth laid the same amount of eggs in monoculture as in intercroppings with high and low clover. White cabbage intercropped with high clover received fewer eggs of the diamondback moth compared with a cabbage monoculture. Intercropping with low clover did not reduce the amount of eggs laid. Intercropping did not appear to affect the emigration of either the leek moth or the diamondback moth. Leek moths were less likely to emigrate than diamondback moths during the first 4 h of the study. We conclude that diamondback moth may be more likely to be controlled by intercropping than leek moths.

We investigated the interaction between the honeydew-producing whitefly Aleurothrixus aepim and tending ants on shrubs of Croton floribundus (Euphorbiaceae) in a semideciduous forest in southeast Brazil. Whitefly eggs underside leaves were tagged during early March 1998 and randomly divided into two experimental groups: control (ants present, n = 75) and treatment (ants excluded, n = 52). During the 75-d experiment, honeydew-collecting ants visited 79% of the control groups of A. aepim. Adults emerged in significantly greater numbers from control than from treatment groups, the latter being heavily attacked by fungi due to accumulation of honeydew. Complete contamination by fungi was three times more frequent at ant-excluded (39%) than at ant-tended (13%) groups. Control groups with low levels of ant-tending produced significantly fewer adults than those more frequently tended by ants. Encarsia parasitoid wasps were more frequently seen on ant-excluded than on control A. aepim groups. Predatory arthropods, however, were equally frequent in either experimental group. This is the first experimental study to demonstrate ant-derived protection in honeydew-producing whiteflies. Given that aleyrodid honeydew can cause considerable damage to the host plant, our results suggest that the honeydew-gathering activity by tending ants is an important factor mediating such multitrophic interaction.

Temperature-dependent development of Carposina sasakii Matsumura was studied, and its stage emergence models were developed. The development times of C. sasakii decreased with increasing temperature up to 32°C in eggs, up to 28°C in larvae, and up to 30°C in pupae. The estimated low-threshold temperatures were 11.0, 9.4, and 10.3°C for eggs, larvae, and pupae, respectively. Thermal constants of eggs, larvae, and pupae were 104.2, 270.3, and 188.7 degree-days, respectively. The stage emergence models of C. sasakii, which simulate the proportion of individuals shifted from a stage to the next stage, were constructed using the modified Sharpe and DeMichele model and the two-parameter Weibull function. In field validation, a degree-day model for the prediction of egg hatch time showed the bias of <1 d between prediction and observation. The stage emergence models predicted the patterns of C. sasakii stage emergences in the field. Also, the established stage emergence models should be useful in building a C. sasakii population model that will describe its seasonal occurrence pattern and population dynamics under various orchard systems.

Adult Colorado potato beetle, Leptinotarsa decemlineata (Say), recruitment on potato plots by flight or by walking occurred throughout the 1991–1993 crop seasons. Most recruitment occurred by walking. Yearly recruitment by flight ranged from 9.5 to 49.4%. It is suggested that the proportion of recruitment occurring by flight is determined largely by environmental factors such as air temperature and solar radiation. The presence of well-developed flight muscles is necessary for flight but was not a limiting factor until late August and even then only for part of the population. The proportion of beetles with developed thoracic muscle masses, developed ovaries, high abdominal fat content levels, and sperm in the spermatheca did not significantly differ between beetle populations recruited by flight or by walking but did differ between the overwintered and summer groups. A significant proportion of beetles that colonized potato plots by flight emigrated from the plots by walking on the same day throughout each crop season. This suggests that most beetles use both flight and walking to disperse throughout the day depending on the “task” and environmental conditions. A large proportion of summer adults in prediapause condition retain the ability to disperse by flight when conditions are appropriate such as in 1991 in this study. Results confirm that potato beetle recruits counted on plants or collected in ground traps have an overall 0.41 sex ratio but those collected in flight traps have a 0.52 sex ratio. There was no indication that the sex ratio plays a significant role in determining the relative contribution of walking and flight to recruitment. A diapausing switch in early August responsible for prediapausing conditions in the summer population of beetles occurs in New Brunswick. The switch did not entirely prevent dispersal to the crop by flight as reported elsewhere for more southern locations.

Aerial dispersal of citrus rust mite, Phyllocoptruta oleivora (Ashmead), in central Florida showed a diel periodicity peaking between late morning and early afternoon. The abiotic factors that best described the dispersal pattern were solar radiation, time, and leaf wetness; whereas wind speed, humidity, temperature, and rainfall had minimal effect. The longevity of adult mites removed from fruit was inversely related to constant temperatures between 25 and 35°C. The longevity of mites removed from fruit at 2-h intervals between 0700 and 1300 hours and exposed to ambient temperature and humidity outdoors was inversely related to the time of removal from the host. There was a linear relationship between the number of mites captured in traps and population density on fruit. Mites left fruit harboring extremely low populations and some fruit supporting dense populations yielded hundreds of dispersing mites per day. Mites were readily carried on air currents between adjacent citrus groves. Nearly all of the mites captured in dispersal traps were adult females, and were found in greater proportions in traps than would be expected from the sex ratio of mites on fruit. Studies using isolated fruit in the laboratory showed that a single virgin or inseminated female could initiate a local population through oedipal mating and sibmating. The data are discussed in relation to the selective forces that may shape the dispersal behavior of citrus rust mite and to the potential impact of aerial dispersal on mite management and the development of acaricide resistance.

Adult females of many arthropods require high food intake for producing eggs, whereas males feed less and spend more time searching for mates. If males and females differentially prioritize activities, they may experience a different ratio of costs to benefits of antipredator behaviors. We investigated sexual differences in the behavioral responses of spotted cucumber beetles, Diabrotica undecimpunctata howardi Barber, to the spider Rabidosa rabida Walckenaer in laboratory arenas in which the beetle could detect the spider, but the spider was prevented from preying upon the beetle. In structurally simple arenas with a single plant, the presence of a spider caused female beetles to spend less time on the plant, and to feed less when on the plant. In contrast, male beetles did not alter their behavior in response to the spider. A second experiment used larger arenas, in which the beetle could choose between a side containing a plant with a spider at its base, and the other side with no spider. Female cucumber beetles spent less time on the side with the spider, whereas males did not consistently change their behavior in response to the spider. The weaker antipredator response of males leads to a greater predation risk, as revealed by a third experiment in which predation was allowed. In this experiment males were 16 times more likely than females to be killed by R. rabida, demonstrating that the lower responsiveness of male beetles to predators increases the risk of being preyed upon.

I examined the impact of Tetraopes tetraophthalmus (Forster) on its host plant, Asclepias syriaca L., through a series of field observations and experiments. Adult beetles feed on milkweed flowers and foliage while larval beetles feed on the rhizomes of milkweed. Strong negative effects of beetle herbivory on milkweed growth, but not sexual reproduction, were found in experiments comparing growth for milkweed patches from which adult beetles were removed to controls with an unmanipulated abundance of beetles. Experiments using potted milkweed revealed a strong negative effect of beetle larvae on the growth of milkweed roots and rhizomes. Under natural field conditions, I could detect no effect of adult beetle density on the growth or sexual reproduction of milkweed. Overall, it appears that below ground herbivory by beetle larvae negatively impacts milkweed growth, but detection of these effects under natural conditions are confounded with a number of factors.

The mealybug Maconellicoccus hirsutus (Green) has extended its range throughout the Caribbean region since it was first detected in Grenada in 1994, and has recently been detected in Southern California, Mexico, and Central America. Laboratory and field experiments using virgin females were conducted on St. Croix, U.S. Virgin Islands, to determine if females attract males with pheromones. Virgin females isolated in gelatin capsules attracted on average one male to each capsule over a period of 18 h in the laboratory compared with gelatin capsules without females. Adhesive traps baited with virgin females and placed on hibiscus, Hibiscus rosa-sinensis L., in the field, captured more males at all three study localities on St. Croix than did unbaited traps. Virgin females attracted more males than controls at 0–10 m from infested hibiscus, but were capable of attracting males at 50 m distance from an infestation. The attractiveness of virgin females to flying males strongly suggests the involvement of a female-produced sex pheromone. Isolation and synthesis of such a sex pheromone would provide a valuable tool for population monitoring and control of this invasive pest.

Spalangia endius Walker, a parasitoid wasp, parasitizes both young and old Musca domestica L. pupae, but parasitization site differed with host age. With young hosts, a mother’s first drill attempt was about equally likely to be on either half of the host; and host half did not affect the number of drill attempts, the proportion of those attempts that were successful, or the duration of the first successfully completed drill. In contrast, with old hosts, mothers tended to attempt drilling sooner and more often on the posterior versus anterior half of hosts; and a greater proportion of drills were successful on the posterior half. Offspring head width did not differ significantly between offspring oviposited on the posterior versus anterior half of hosts, regardless of host age. Once adult, most offspring chewed out through the anterior half of the host, regardless of host age.

Integrating global positioning systems technology with a visual canopy survey, a 1-m level of sampling support was used to explore within-field spatial organization of the Colorado potato beetle, Leptinotarsa decemlineata (Say), in potatoes. Spatially referenced counts of adult and large larvae (third and fourth instar) L. decemlineata were made in four ≈1.5-ha untreated potato fields during two Pennsylvania growing seasons. The presence and nature of spatial structure varied with developmental stage. Overwintered, immigrating adults established ‘trends’ or ‘drift’ in the mean density, but spatial dependency (covariance structure) was not detected. This, coupled with a high incidence-to-mean density relationship, suggests a within-field dispersive role for the colonizers. Large larvae and F₁ adults, in contrast, displayed spatial dependency (covariance structure), at times accounting for up to ≈45% of the variation. Their relatively lower incidence-to-mean density relationship suggests less within-field mobility during the reproductive phase of the population cycle. These observations imply that, although an insect population’s spatial structure may be difficult to characterize due to its dynamic nature, there is a consistent and predictable pattern in L. decemlineata spatial structure that is linked to its population phenology.

Heteroblasty describes plants with juvenile and adult vegetative shoots that differ morphologically. Virtually nothing is known about the affects of this source of within-plant variation on host-plant selection by herbivorous insects. This is the first study on the use of visual cues by insects that specialize on different shoot types of a heteroblastic plant. Two psyllid species (Ctenarytaina eucalypti Maskell and C. spatulata Taylor) specialize on glaucous juvenile and glossy adult shoots of Eucalyptus globulus Labill., respectively. We compared their responses to artificial colors and to the colors of expanding and expanded juvenile versus adult leaves. Sticky traps were used to compare psyllid response to seven artificial colors. A “color tube” was developed to compare psyllid responses to leaf color. Both psyllid species preferred yellow traps over all other colors (red, blue, green, white, and clear), and color preference was independent of species. Both species were also more attracted to the colors of expanding and expanded juvenile leaves than to adult leaves. Although the psyllids perceived differences between the colors of juvenile and adult leaves of E. globulus, their responses suggest that leaf color alone is not the basis of discrimination between foliage types.

Paired suction traps were used to study the habitat choice of migrating aphids in adjacent crop and natural habitats in east central Illinois. Traps were placed in a row-crop field and a restored prairie for 4 yr at one site, and a row-crop field and a wooded plot for 3 yr at another. Row crops were corn or soybean, rotated annually. We did not wish to sample aphids that were native to the local habitats because they would be in a habitat by circumstance of birth, and not necessarily by choice. We therefore removed from the habitat choice analysis any aphid species that colonize plants in either the agricultural or natural habitat. Numbers of aphids from outside sources in the two adjacent habitats were compared. In 2 of 4 yr, outside-source aphids were more abundant in the row-crop than the restored prairie, despite the absence of potential host plants in both habitats. In all 3 yr, outside-source aphids were trapped in greater numbers in the crop than in the woods. Selection of the crop over the natural habitat occurred during almost all sampling periods throughout the summers. We present possible explanations for the aphids’ apparent preference for crop habitats and provide brief discussions of abundant aphids, local—as well as outside—source species, trapped in our study. We also discuss the relevance of our study to the understanding of long- and short-distance aphid migration and aphid vectoring of plant pathogens.

In the laboratory, the timing of both preflight and flight behaviors of the Asian strain of female gypsy moths, Lymantria dispar L., was regulated primarily by light intensity. The shortest times to initiation of wing fanning and flight occurred at 0.1 lux, the lowest light intensity evaluated. A gradual decrease in light intensity, compared with an instantaneous decrease, prolonged time to flight. The highest percentage of female flight was observed at 0.1 lux. A higher percentage of females initiated flight when exposed to lower light intensities after the onset of normal scotophase rather than before scotophase. Virgin females were less likely to fly than mated females. Females fanned their wings longer at lower temperatures and when they were capable of only a gliding flight. Females that were flight-tested the same day they emerged tended to take longer to initiate flight than those 1–2 d old. At 0.1 lux, the majority of the Asian females, less than 2% of the F₁ hybrid females, and none of the North American females exhibited strong, directed flight. Over half of the F₁ hybrids glided for a few meters while flapping their wings, whereas none of the North American females exhibited even this level of flight. Thus, female flight capability will be reduced when flighted and nonflighted forms initially hybridize.

We tested the concept of using a carbohydrate-based mosquito control method on saltmarsh mosquitoes. In laboratory trials, xanthan gum, a type of carbohydrate gum thickener, killed both fourth-instar and pupae of Aedes sollicitans (Walker). The lethal time 50 was shorter for the pupae than the fourth instars, 35.8 and 61.2 min, respectively. In a screen of commercially available carbohydrate gum thickeners and starches we did not find any compounds that had properties, other than xanthan gum, useful for testing the concept of carbohydrate-based mosquito control. Therefore, in the field study, we tested xanthan gum at the maximum rates used previously, 22 g/m². This allowed us to test the concept of using such a control strategy in field conditions. Under these conditions, xanthan gum increased the Ae. sollicitans mortality rate to 67% (±3.9% SE), a level not significantly different from the Abate treatment, 73% mortality (±7.7% SE). We also examined the effect of xanthan gum and a commercially available starch, National 5370, on the biological oxygen demand (BOD) in the marsh environment. This allowed us to determine at what rate a practically applicable carbohydrate would have to be delivered to the marsh environment such that the BOD is not affected. Our initial findings suggest a practically applicable carbohydrate-based mosquito control agent would have to be delivered at or below 2.2 g/m².

The effect of a UV-deficient environment on the attraction and dispersal behavior of whiteflies, Bemisia argentifolii (Bellows & Perring), and on the transmission efficiency of the whitefly-borne tomato yellow leaf curl geminivirus, was tested under field conditions and through controlled experiments. We found that the rate of tomato yellow leaf curl virus-disease spread to tomato plants grown under walk-in tunnels covered with regular greenhouse plastic sheets increases sharply with time, whereas the virus infection-rate under UV-absorbing sheets proceeds at a very slow pace. Average number of whiteflies trapped under regular plastic sheet tunnels was significantly higher than numbers trapped in UV-absorbing plastic sheet tunnels. Similarly, the average number of whiteflies trapped on yellow-sticky traps placed on the outside walls of tunnels covered with regular plastic was higher than the number trapped on the outside walls of tunnels covered with UV-absorbing plastic sheets. No differences were found in the whitefly’s ability to transmit tomato yellow leaf curl virus under the two types of plastic covers. Whitefly dispersal pattern under the two types of plastic covers was examined using a release-recapture experiment. In each type of walk-in tunnel we established a grid of yellow-sticky traps forming two concentric circles: an inner and an external. Under UV-absorbing tunnels, significantly higher numbers of whiteflies were captured on the internal circle of traps than the external circle. The fraction of whiteflies that were captured on the external circle was much higher under regular covers, when compared with UV-absorbing covers, suggesting that filtration of UV light hindered the ability of whiteflies to disperse inside these plastic tunnels. Our results indicate that the mechanisms by which UV-deficiency protects covered crops from insect infestation and spread of viruses are that the lack of UV interferes with insect flight orientation; and that the lack of UV radiation alters the normal behavior of the invading insects, resulting in reduced dispersal activity.

Unbiased samples from insect traps are dependent on the placement of traps to account for variation in the spatial distribution of insect fauna. In forests, the spatial distribution of insects reflects forest vertical structure. However, comparative studies of insect diversity in managed forests have traditionally focused a single forest stratum (e.g., forest floor, canopy). We evaluated the importance of sampling along a vertical gradient to assess the effects of silvicultural treatments on insect fauna. We compared the catch from flight-intercept traps suspended at 1, 3, 5, 7, 9, and 11 m above the forest floor in eight forest stands representing three management types: two clearcut stands, two shelterwood stands, and four selection stands. The vertical distribution of insects was significantly different across the three management systems. A greater proportion of the insect fauna was recovered close to the forest floor in clearcut stands than in selection and shelterwood stands. Some insect taxa were restricted to the higher traps; whereas other taxa showed different height associations across the three management systems. Therefore, vertical sampling is important to compare the insect fauna in managed forests differing in vertical structure.

Commercial non-Bacillus thuringiensis (Bt) corn was planted adjacent to Bt corn to determine the effects of Bt corn pollen falling on non-Bt plants for control of European corn borer larvae, Ostrinia nubilalis (Hübner). Field plots in Iowa and Kansas consisted of two center rows of Bt corn with eight rows of adjacent non-Bt corn on each side. In mid-September 1996 and 1997, we counted European corn borer larvae and larval tunnels in the stalk and ear shank. There were no significant differences in European corn borer numbers across non-Bt rows and the slope of the regression line was not significantly different from zero. In a single plot in Iowa, however, fewer tunnels were observed in rows of corn that were closer to Bt corn. This site was isolated from natural infestations and probably does not reflect a typical field situation. Our results suggest that Bt pollen has minimal or no control of European corn borer larvae in adjacent rows of non-Bt corn under natural conditions. Bt pollen drifting onto adjacent non-Bt plants should not increase the risks related to resistance management.

Limb jarring samples were taken in four experimental apple orchards (one completely unmanaged; one with horticultural management and no pest management; one with horticultural management, no pest management, and interplanted with peach and sour cherry; and one under conventional commercial management practices) at hourly intervals over a 24-h period at four times in 1991. A total of 1,176 individual predators belonging to seven orders and 22 families was collected. The most abundant species was Coniopteryx sp. (Coniopteryigidae: Neuroptera), and the most abundant family was Coccinellidae (Coleoptera). A total of 396 adult parasitoids was collected from 26 families of Hymenoptera and one Diptera family, with Encyrtidae being the most abundant. All other individuals were classified as potential food items and were identified only to order or, in some instances, family. A total of 5,812 potential food items was collected. Diversity of predators and parasitoids was greatest in May and June. Diversity of predators was highest on apple trees that were inter-planted with peach and cherry trees, whereas parasitoid diversity was greatest on peach trees and on insecticide treated apple trees. Chrysopids (Neuroptera), clerids (Coleoptera), and Leptothrips mali (Fitch) (Phlaeothripidae: Thysanoptera) were most commonly collected at dawn or during the night, suggesting that their role in orchards may be underestimated by sampling only during daylight hours. With the exception of Scelionidae and Platygastridae (Hymenoptera), parasitoids were most commonly collected during the night. Results indicate that peach trees are attractive to both predators and parasitoids and therefore may be a valuable addition to apple orchards to enhance the abundance of biological control species.

Field experiments were conducted to identify predators of southern masked chafer, Cyclocephala lurida Bland, and Japanese beetle, Popillia japonica Newman, eggs in turfgrass soil and to measure the predation that occurs. Identification of egg predators was determined by direct observation through buried Plexiglas plates of artificially placed eggs. Predation rates of Japanese beetle eggs was further measured using buried bait stations filled with eggs. Up to 73% of eggs in the soil were taken within a 72-h period. Ants were found to be the predominant predator accounting for up to 83% of the eggs taken. One species of ant, Solenopsis molesta (Say), proved to be the primary ant predator of eggs in turfgrass.

A prey-specific gut content enzyme-linked immunosorbent assay (ELISA) was used to identify predation of eggs of bollworm, Helicoverpa zea (Boddie), by Orius spp. in commercial cotton fields in Texas. Degradation of the egg protein began immediately after O. insidiosus fed on an egg. However, the protein antigen was detectable in the predator for approximately 10 h after feeding. The antigen retention time provided a conservative estimate of predation and insured that when predation was detected it occurred on the day predators were collected. The percentage of individual of Orius spp. that was positive by ELISA for the egg antigen varied throughout each growing season. The highest frequency of positive responses occurred before cotton bloom and after peak bloom.

The phenological synchrony of Eustenopus villosus (Boheman) with its host, yellow starthistle, Centaurea solstitialis L. (Asteraceae: Cardueae), was studied in Idaho in 1995 and 1996. Field plots were observed for adult weevil activity periodically throughout the growing season, and yellow starthistle capitula were examined for adult feeding damage, oviposition damage, and larval development. At the study site, weevil phenology was well synchronized with C. solstitialis. Immature capitula, fed upon by adults, were abundant when E. villosus began to emerge in late May. During both years, the number of weevils and capitula increased throughout June. Adult females fed on capitula for about 2 wk. Weevil ovary dissections revealed that ovaries were mature after a 2-wk period of feeding. The development of mature capitula during late July corresponded to the initiation of oviposition. Eustenopus villosus, unique among the phytophages introduced for C. solstitialis biological control, attacks four plant stages resulting in observable impact to buds. Damaged buds either died or became distorted. Weevil feeding damage on young and mature capitula may make this insect a highly effective control agent.

Examination of Formosan subterranean termites, Coptotermes formosanus Shiraki, for possible biological control agents revealed the presence of 15 bacteria and one fungus associated with dead termites from New Orleans, LA, USA. All but one of the bacteria species were gram-negative bacteria. Bacterial isolates from dead termites were primarily Serratia marcescens Bizio that caused septicemia in C. formosanus and also appeared to contain proteolytic enzymes. Multiple strains of S. marcescens were isolated. Six of the eight strains of S. marcescens were red, probably not pathogenic in humans, and candidates as biological control agents for C. formosanus. Bacteria isolated from termite substrata included Corynebacterium urealyticum Pitcher, Acinetobacter calcoacet/baumannii/Gen2 (Beijerinck), S. marcescens, and Enterobacter gergoviae Brenner. Some of these bacteria are potential human pathogens. Forced exposure bioassays demonstrated that the T8 strain of S. marcescens killed 100% of C. formosanus by day 19.

The biological control of termites may be facilitated if their highly evolved immune systems can be suppressed. Eicosanoids are C20 polyunsaturated acids that are of widespread biochemical importance, including their role in protecting insects from bacterial infection. In laboratory experiments, the eicosanoid biosynthesis inhibitors dexamethasone, ibuprofen, and ibuprofen sodium salt were each provided along with a red-pigmented isolate of Serratia marcescens Bizio, a bacterial pathogen, to the Formosan subterranean termite, Coptotermes formosanus Shiraki, by means of treated filter paper. The increased mortality that resulted with dexamethasone and ibuprofen supported, but alone was insufficient to prove, the hypothesis that the termites’ immune systems were suppressed by these compounds, making the insects more vulnerable to infection by S. marcescens. This effect on mortality was noted only at 3.4 × 10¹⁰ colony-forming units per milliliter, a high treatment level. A significant amount of the infection and subsequent mortality may have resulted from direct contact with the bacterium and the remainder from its ingestion. Water-soluble ibuprofen sodium salt demonstrated a protective effect that was unexpected in light of the increased termite mortality observed with the relatively water insoluble, free acid form.