The overwintering survival of Urophora affinis Frauenfeld and U. quadrifasciata (Meigen) was examined in a 5-yr (1989–1993), multiple-site field study in western Montana. These two tephritid fly species are introduced biological control agents of spotted knapweed, Centaurea maculosa Lamarck, and diffuse knapweed, Centaurea diffusa Lamarck. Significant differences in overwintering mortality of U. affinis and U. quadrifasciata larvae (whether occurring conspecifically or heterospecifically within the same capitulum) were found among sites. Overwintering mortality of U. affinis and U. quadrifasciata (whether occurring conspecifically or heterospecifically within the same capitulum) showed no relationship with site elevation. Overwintering mortality of U. affinis and U. quadrifasciata showed no relationship with the densities of conspecific or heterospecific galls found within the capitula. Extended periods of extremely cold temperature were found to explain most of the variation in overwintering mortality of both fly species. We conclude that periods of extremely cold temperature is the most important mortality factor affecting overwintering survival in U. affinis and U. quadrifasciata.

The foraging activity of pollinator insects in relation to weather factors (ambient temperature, solar radiation, relative humidity, and wind speed) was studied in an apple orchard with special reference to two managed bee species, Osmia cornuta (Latreille) and Apis mellifera L. Over the range of observed weather values, A. mellifera activity was significantly dependent on temperature, solar radiation, and wind speed; O. cornuta activity was dependent on solar radiation and wind speed. These results were confirmed through video recordings at one O. cornuta nesting shelter and one A. mellifera hive. For both species, daily activity started at lower temperatures than it ceased, whereas solar radiation did not differ between these two events. In general, O. cornuta was active from 10 to 12°C and 200 w/m², and A. mellifera from 12 to 14°C and 300 w/m². O. cornuta was the only bee species seen visiting apple flowers under strong wind or light rain. Because of its greater tolerance to inclement weather, O. cornuta pollinated apple flowers for longer periods (both daily and seasonally) than other flower visitors.

We investigated the overwintering biology of four temperate-latitude bark beetles: Dendroctonus frontalis Zimmermann, Ips pini (Say), I. grandicollis (Eichhoff), and I. perroti Swaine. All four species were freeze-susceptible. However, there was variation within and among species in overwintering biology that related to their geographic distribution. D. frontalis and southern populations of I. grandicollis continued to reproduce and develop under the bark of their host plants throughout the winter and did not show any seasonal adjustments in their lower lethal temperatures: mean supercooling point ± SD = −12.15 ± 4.02 and −12.25 ± 2.50°C. In contrast, northern populations of I. grandicollis and I. pini employ a behavioral strategy in which adults migrate to the forest soil, where they are insulated from temperature extremes by litter and snow. Furthermore, adult supercooling points of both northern populations declined from about −13°C in summer to about −17°C in early winter. A concomitant decline in lipid content suggests that lipid metabolism may be involved in seasonal adjustments of cold tolerance in I. pini. An assortment of temperature manipulations failed to provide any evidence of cold tolerance acclimation. Immatures, which remain in the inner bark of their host trees, have lower lethal temperatures of −5 to −12°C, and are especially vulnerable to mortality from freezing. I. perroti, a northerly distributed species, had similar cold tolerance and overwinter behavior as northern populations of the other two Ips species. Winter mortality from freezing could be an important determinant of population dynamics in all four species. Understanding variations in cold tolerance and overwinter behavior among insects species may help predict population dynamics and distribution of potential pests.

Pheromone gland extracts of grape berry moth females, Endopiza viteana Clemens, contain the main pheromone component, Z9–12Ac, at ≈1.2 ng per female, together with both geometric isomers of 11–14Ac, and a number of saturated acetates and alcohols of the chain length 12–16. The analogous alcohol, Z9–12OH, was found in some gland extracts. Trap capture of males was significantly increased by adding 0.5 or 2 μg of Z11–14Ac to 10 μg of the main compound, Z9–12Ac; whereas, adding 0.5 or 2 μg of E11–14Ac had no significant effect. In contrast, the addition of 5% Z9–12OH to the main compound resulted in a strong reduction in trap capture. Traps baited with a blend of Z9–12Ac and its geomeric isomer, E9–12Ac, which was not detected in gland extracts, were significantly less attractive than traps baited with blends of Z9–12Ac and Z11–14Ac. Knowledge of pheromone components and antagonists is essential for development of the mating disruption technique. The compounds identified in E. viteana are behaviorally active in the three most important tortricid pests of grape, Vitis vinifera (L.), in Europe. It may thus be possible to use a single blend of synthetic pheromone for control of several species.

Toxicity of three mosquito oviposition repellents, N,N-diethyl-3-methylbenzamide (AI3-22542 or deet), AI3-35765, and AI3-37220 to 6 aquatic nontarget invertebrates, was evaluated in the laboratory. The 24-h LC₅₀ values for Cypricercus sp. (Ostracoda), Moina sp. (Cladocera), Eucyclops agilis Koch (Copepoda), Strelkovimermis spiculatus Poinar & Camino (Nematoda), first- and fourth-instar Toxorhynchites amboinensis Doleschall larvae (Diptera), and fourth-instar Chironomus decorus Johannsen larvae (Diptera) ranged from 0.012 to 0.127% or 120 to 1,270 ppm. Cypricercus sp., Moina sp., E. agilis, first-instar Tx. amboinensis and fourth-instar C. decorus were generally more sensitive to the test repellents than male and female S. spiculatus and fourth-instar Tx. amboinensis. Male S. spiculatus was more sensitive to the repellents than its female and this was probably because of the smaller body size of the male. All invertebrates were generally more sensitive to AI3-37220 than to deet and AI3-35765. The experimental repellents were considered safe to the aquatic nontarget organisms when employed as oviposition repellents for Aedes albopicus (Skuse) mosquitoes.

A series of bioassays were performed to evaluate the effects of host tree monoterpenes on initial entry, within-tissue orientation, and gallery construction by the bark beetle Ips pini (Say). Monoterpenes at concentrations present in host trees affected all stages of postlanding host acceptance behavior. However, the effects of each monoterpene varied with the particular stage of the orientation sequence. The number of beetles entering a phloem-based medium decreased with increased concentrations of most monoterpenes. An exception occurred with β-pinene, which elicited increased beetle entry at moderate concentrations. Once beetles began to form galleries within phloem-based media, higher monoterpene concentrations increased the likelihood that they would move from amended to nonamended sections of the substrate. However, low to moderate concentrations of β-pinene arrested beetles within treated regions of the arena. The total gallery length generally decreased with increasing monoterpene concentrations. However, gallery lengths were consistently higher at intermediate concentrations of α-pinene. The enantiomeric composition of ∂-pinene did not influence entrance or gallery formation by I. pini. Moreover, the concentration of monoterpenes appears to be more important than the type of monoterpene in affecting postlanding host selection behavior. There was a positive correlation between host entry and total percentage of lipids within beetles. We describe a new bioassay that evaluates initial host entry by bark beetles, a critical qualitative decision in their life history, and relates this decision to quantitative aspects of host chemistry. Our results indicate that postlanding host acceptance is a multistep process shaped by environmental conditions and internal physiological state of the insect.

Molting and pupating insects are especially vulnerable to natural enemies and one possible component of their defensive strategy is the selection of suitable microhabitats. We hypothesized that larvae of the lady beetle Coleomegilla maculata lengi Timberlake select molting and pupation sites that effectively reduce their susceptibility to intraguild predation. We characterized microsites on potato plants and evaluated their associated risk of predation by the lacewing Chrysoperla rufilabris Burmeister (Neuroptera: Chrysopidae), a common intraguild predator. The majority of molts (>60%) occurred on potato plants in sites similar to those used by mobile coccinellid larvae. In contrast, 90% of the larvae left the plant to pupate. Second, third, and fourth instars selected artificial shelters for both molting and pupation when these were available. Vulnerability of pupae and newly molted larvae to lacewing larvae depended on plant microsite, with leaves supporting an aphid colony as the most risky sites. Molting and pupating microhabitat selection by coccinellid larvae appears to be a trade-off between the advantages of remaining close to the aphid resource, and the costs of being exposed to intraguild predators.

We ran 10 Malaise traps along a latitudinal gradient in five old-growth forests: San Felasco Hammock, FL (30° N, 82° W); Tall Timbers Research Station, FL (31° N, 84° W); Hitchiti Experimental Forest, GA (33° N, 84° W); Patuxent Wildlife Research Center, MD (39° N, 77° W), and Shaw Woods, Ontario (46° N, 77° W). Of 18,791 ichneumonid wasps collected, 1,487 campoplegines and 4,494 ichneumonines were sorted to 241 species (95 species of Campopleginae and 146 of Ichneumoninae). Campoplegine species richness was highest at the Georgia site: San Felasco (20 species), Tall Timbers (32), Hitchiti (49), Patuxent (35), and Shaw Woods (12). Ichneumonine species richness was highest at the Maryland site: San Felasco (47), Tall Timbers (30), Hitchiti (44), Patuxent (68), and Shaw Woods (37). The results confirm reported trends that peak North American ichneumonid species richness lies at midlatitudes. However, they document greater biodiversity in the southern states and a broader peak than previously reported.

The role of reduced-impact logging on the preservation of biodiversity in tropical lowland dipterocarp rainforest is examined by looking at differences in dung beetle community structure between two sites logged in 1993: one harvested using reduced-impact methods and one using conventional techniques. Collections were made using two flight intercept traps over 7 d, and samples were compared with previous collections made from primary forest (riverine and interior-forest) and older forest logged using conventional techniques (logged in 1981). Of the two 1993 sites, the higher diversity and species richness (S = 57, n = 969, alpha = 13.23, H′ = 3.24) was recorded in the forest logged using reduced-impact techniques: the conventionally logged site had both lower diversity and species richness (S = 48, n = 1968, alpha = 8.88, H′ = 1.89), and lacked some primary forest specialists present in the reduced-impact forest samples. The dung beetle community in the 1993 conventional logged site is similar to that of the conventional logging site harvested in 1981. Primary forest has a well-defined ecotone, from interior to riverine forest: both 1993 sites contain a mixture of interior-forest and riverine specialists that are usually spatially separated along this ecotone. Although the dung beetle assemblage in the forest harvested by reduced-impact logging is more similar to a primary interior-forest assemblage than the conventionally logged site, both 1993 sites have assemblages that are closer in similarity to assemblages from primary-riverine habitat than they are to ones from primary interior-forest. However, because the forest logged using reduced-impact logging techniques has a more equitable and diverse dung beetle assemblage and a greater number of interior-forest specialists than the conventionally logged site, this study suggests that reduced-impact logging has better preserved the primary forest assemblage than conventional logging techniques.

Previous studies have postulated that the quality of resources that female gypsy moths, Lymantria dispar (L.), allocate to their eggs may affect the growth, development, and population dynamics of larvae in subsequent generations. To test this hypothesis, we collected eggs from food stressed and unstressed populations and measured critical life history parameters (e.g., dispersal, growth rate, mortality, fecundity) of gypsy moth larvae with a combination of field and laboratory experiments. Larvae from stressed and unstressed source populations showed no differences in overall dispersal, mortality from pathogens and parasitoids, or developmental rate. In smaller laboratory and field rearing studies, there were no significant differences in the relative growth rates, female pupal weights, or fecundity between larvae from stressed and unstressed populations. However, we found that the proportion of males in egg masses from stressed populations were 11% higher than those from unstressed populations. In addition, there was a significant relationship between egg mass size and proportion of males in one of 2 yr of the study. We conclude that nutritionally mediated maternal effects have a relatively minor influence on the population dynamics of the gypsy moth.

We have been studying the factors that control larval diapause of Sesamia nonagrioides (Levebvre), a multivolitine pest of corn, Zea mays L., in the Mediterranean. The effect of various combinations of photoperiod and temperature on the induction of larval diapause of S. nonagrioides was examined. Short daylengths (8–12 h) were the main factor inducing diapause in this species, whereas high temperatures could avert the effect of the photoperiodic signal. Daily temperature cycles with different amplitudes (differences between the thermophase [high phase] and cryophase [low phase] temperatures), could induce diapause under a photoperiod of 12:12 (L:D) h when the cryophase coincided with the scotophase (dark period). In contrast, short daylengths had no effect on diapause when the thermophase coincided with the scotophase. Moreover, greater differences between the high and the low temperatures of the thermoperiod led to a higher incidence of diapause. Diapause also occurred under 24-h thermoperiods at constant darkness; the incidence of diapause correlated with the duration of the cryophase. The thermoperiodic response curve of diapause under constant darkness was analogous to that of the photoperiodic response of a type I, or long-day insect. The cryophase of the thermoperiod must be <17.5°C to obtain a high incidence of diapause. Consequently, it appeared that a thermoperiodic threshold during the cryophase was demonstrated. Hence, both the duration and the temperature of the cryophase of the thermoperiod were important factors controlling the diapause response. The ecological implications of this behavior are discussed.

Dissection of digestive tracts showed that five bark beetle species, Ips paraconfusus Lanier, Dendroctonus jeffreyi Hopkins, Tomicus piniperda (L.), Scolytus multistriatus (Marsham), and Phloeosinus sequoiae Hopkins, feed beneath the bark as callow adults before emergence from their brood trees. T. piniperda, S. multistriatus, and P. sequoiae also feed in host shoots before colonizing trees in which reproduction occurs. Callow I. paraconfusus and D. jeffreyi were found to ingest food material once the cuticle became yellow, whereas callow T. piniperda and S. multistriatus did not feed until their cuticles were light brown and black, respectively. Feeding behavior differed between the sexes only in D. jeffreyi, in which yellow males contained less food material than yellow females. Yellow I. paraconfusus removed from beneath the bark of Monterey pine, Pinus radiata D. Don, did not blacken without additional feeding, and some starved, brown adults became black. Callow adults that were allowed to feed survived longer and became darker-colored individuals more frequently than starved beetles. The potential benefits of pre-emergence feeding are discussed.

Published anecdotal reports suggest that Japanese beetles, Popillia japonica Newman, feed more heavily on host plants growing in full sun than on shaded plants. We studied the effects of shading on foliar characteristics of roses (Rosa variety floribunda ‘Class Act’) and determined preference and fecundity of beetles provided with sun- or shade-conditioned leaves. Defoliation by P. japonica also was compared between sun-grown and experimentally shaded roses in the field. Leaves from plants grown in full sun were smaller and thicker than ones from shaded plants, with slightly higher tannins. Leaf toughness and nitrogen levels were not affected by shading, but leaves from sun-grown plants had relatively higher sugar content. Beetles consistently consumed more foliage from sun-grown plants than from shade-grown plants in laboratory preference tests. However, beetles fed continuously for 2 wk on leaves from sun- or shade-grown plants had similar fecundity. In the field, beetles fed somewhat more heavily on foliage of roses grown in full sun than on plants grown under cloth canopies that provided 73% shading. Plants grown under semitransparent canopies of spun-bonded fabric sustained intermediate damage, suggesting that one way that shading may reduce defoliation is by rendering the shaded plants less apparent or accessible to host-seeking beetles. Implications of this work for understanding feeding behavior of P. japonica, and for pest management through planting site selection, are discussed.

We studied the effects of date of hatch, maternal population quality, larval density, air temperature, and host foliage on the dispersal of neonate gypsy moths, Lymantria dispar (L.), under field conditions. Larval dispersal significantly increased with date by nearly fourfold, but neither maternal population quality nor crowding had a significant effect on dispersal activity. Neither variation in air temperature or length of egg chill were related to the increase in dispersal with date; this trend was best explained by the combined effects of foliar changes during leaf expansion and declines in host quality because of induced plant defenses. Our results indicate that environmental factors in the current generation, such as leaf expansion after budburst, have a much larger influence than maternal population quality on the dispersal of neonate gypsy moths under natural conditions.

The ear borer Mussidia nigrivenella Ragonot is a polyphagous insect pest that feeds on various cultivated and wild plants. Surveys in four agro-ecological zones of Benin, conducted between 1993 and 1997, revealed ≈20 plant species from 11 plant families hosting the borer, but only 13 host plants enable the borer to develop to the pupal stage. Whereas, a maize crop usually supports one generation per season, several generations of M. nigrivenella were recorded on Parkia biglobosa (Jacq.) Benth. and Gardenia spp. Agro-ecological variation in the availability of wild host plants was noticed. The high abundance of wild hosts in the Guinea Savannas reflects the diversity of the natural flora in these zones. This abundance of M. nigrivenella host plants, coupled with their overlapping fruiting periods may be the main reason for the high pest densities on maize, although only one maize crop per year is grown in the Northern Guinea savanna. In a field experiment, the highest infestation levels and densities of M. nigrivenella occurred on Canavalia enseiformis (L.) DC. and Mucuna pruriens DC., two popular cover crops in West Africa. Maize and cotton were about equally suitable hosts. Thus, fruiting periods of C. enseiformis and M. pruriens should not precede that of maize, to avoid emerging M. nigrivenella populations shifting from the cover crops to maize.

Foraging trails of the ant Formica neogagates Emery on leaves of trees and shrubs in the forest or on artificial leaves in a laboratory arena were recorded and digitized. About the same proportion of a leaf was explored by ants whatever the plant species or size of leaf. The portions and numbers of leaves revisited by ants were consistent with the hypothesis that ants do not recognize areas they have recently explored. Trail characteristics of ants foraging on artificial laboratory leaves were similar whether or not leaves had a drop of honey at their base, except that on leaves with honey, more trails occurred and large turning angles were more frequent. By continually watching ants as they climbed up and down tree trunks in the forest, I was able to deduce that up to 150 individuals of F. neogagates may be in a tree at any one time, and that some ants forage in trees for at least 4 h at a time. At this foraging intensity, a significant fraction of the leaves on a tree could be explored by these ants in a day.

Attack rates of the parasitoid Leptomastix dactylopii (Howard) were examined in petri dishes and on caged plants that varied in architectural characteristics. Individual female parasitoids were placed into petri dishes containing a range of densities of the citrus mealybug, Planococcus citri (Risso). Green and yellow-variegated coleus, Solenostemon scutellarioides (L.) Codd, were used to determine the effects of plant architecture on the rate at which L. dactylopii parasitized citrus mealybugs. Coleus plants were categorized into size classes based on height, number of leaves, leaf surface area, and number of branches. A single mated female L. dactylopii was placed into each plastic observation cage containing a plant with 1, 8, or 16 third- to early fourth-instar mealybugs and allowed to forage for 24 h. After this time, citrus mealybugs were removed from coleus plants and placed into petri dishes that were checked after 10 d for mummified citrus mealybugs, the measure of a successful attack. L. dactylopii were unable to find a host after 24 h when only one citrus mealybug was present in the searching environment. Higher attack rates occurred as the number of mealybugs increased in the petri dishes. L. dactylopii attacked an average of 15.6 ± 2.3 mealybugs within a 24-h period. Higher attack rates were evident as the number of citrus mealybugs increased on caged plants. Plant color had no effect on the attack rate of L. dactylopii. All architectural characterizations of plant size, height, leaf number, leaf surface area, and branch number were negatively correlated with parasitoid attack rate. These findings suggest that biological control practitioners may use any convenient measure of plant size (e.g., height) to modify the release rate of L. dactylopii in a citrus mealybug management program.

DAS-ELISA, immunohistochemistry and electron microscopy were used to investigate the association of the causal agent of bacterial wilt, Erwinia tracheiphila (Smith), within the beetle Acalymma vittatum (F.). After a 24-h acquisition period, a high percentage of individuals tested positive for E. tracheiphila antigen using both immunohistochemistry (100%) and DAS-ELISA (70–60%). Both assays showed that the antigen remained in beetles long after the initial acquisition, with the percentage declining during incubation. Using ELISA, the percentage decreased to 4.7% within 3 d after acquistion, then increased to 10% within 10 d and remained at 10% for 30 d. Immunoperoxidase assays of paraffin embedded gut sections were more sensitive, and showed that 95% of the beetles harbored the pathogen after 10 d and 20% after 30 d. E. tracheiphila antigen was present throughout the digestive tract soon after acquisition, but only small clusters of E. tracheiphila were observed along the alimentary canal 3 d after transfer onto clean plants. After 10 and 30 d on clean plants, E. tracheiphila antigen reaction was stronger and clusters of bacteria were more numerous, primarily in the posterior midgut and anterior portion of the hindgut. Scanning electron microscopy and TEM photomicrographs confirmed the presence of bacterial cells resembling E. tracheiphila associated with the intima of the hindgut 1 and 30 d after acquisition. This demonstrated the sensitivity of immunohistochemisty for detecting E. tracheiphila within its vector, and suggests a long-term extracellular endosymbiotic association of E. tracheiphila with the alimentary canal of A. vittatum.

Populations of Callirhytis cornigera (Osten Sacken) and its associated community of natural enemies and inquilines were monitored on pin oak, Quercus palustris Muenchhausen, in Lexington, KY, from 1997 to 1999. The gall wasp has alternating agamic and sexual generations that differ morphologically and develop in multichambered galls on branches and single-chambered galls on leaves, respectively. There was a strong association between maximum gall diameter and the number of total stem gall inhabitants, such that proportionately more C. cornigera survived and fewer were parasitized as stem gall diameter increased. The most abundant natural enemies of the agamic generation included the hymenopteran parasitoids Sycophila spp. (Eurytomidae) and Ormyrus labotus Walker (Ormyridae), and the clerid predator Phyllobaenus verticalis (Say). The most abundant inquilines in stem galls were the cynipids Synergus sp. near lignicola and Ceroptres sp., and the dogwood borer, Synanthedon scitula (Harris) (Lepidoptera: Sesiidae). In leaf galls, Aprostocetus sp. was the most abundant parasitoid, and Ceroptres sp. was the only inquiline. The unique aspects of the C. cornigera gall system are discussed, including the relative abundance, emergence phenology, and host relationships of C. cornigera and its associated natural enemies and inquilines.

Egg incubation and nymphal development of the consperse stink bug Euschistus conspersus Uhler were studied in laboratory growth chambers under constant and fluctuating temperatures. Eggs did not hatch at 10, 12, and 37°C, and separately placed first-instar nymphs did not survive to become adults. Egg incubation and total nymphal development times were significantly shorter at 32°C than compared with the lower temperatures. Egg incubation and total nymphal development at the fluctuating temperature fell between the two optimal constant temperatures of 27 and 32°C. Linear regression of developmental times and constant temperatures for egg incubation, first–third instar nymphal development and fourth–fifth instar nymphal development provided an estimated lower developmental threshold of 12°C for E. conspersus. This threshold was used to develop a phenology model. Field validation of the model was based on canopy shake samples and pheromone trap captures obtained from processing tomato, Lycopersicon esculentum Miller, fields. Results supported the laboratory phenology model. Field observations supported the trap’s potential as a degree-day biofix in processing tomatoes.

The objective of our research was to identify alternatives to synthetic pesticide treatments to prevent aphid outbreaks in greenhouse lettuce crops. In the laboratory, we determined the susceptibility of three lettuce-infesting aphid species, Macrosiphum euphorbiae (Thomas), Myzus persicae (Sulzer), and Nasonovia ribisnigri (Mosley), to the hyphomycete Verticillium lecanii (Viegas) (strain Vertalec), the plant triterpenoid molecule azadirachtin (BioNeem), and an insecticidal soap (Safer’s). Estimated LC₅₀ and LT₅₀ obtained in the laboratory indicated that the three aphid species were susceptible to the entomopathogenic fungus, the plant extract, and the soap. Under greenhouse conditions, we assessed the potential of the three pesticides to reduce aphid populations and compared it with that of a synthetic insecticide, the organophosphate Malathion. Greenhouse experiments demonstrated that all three pesticides significantly reduced the population of each aphid species compared with the untreated plants. This study also revealed differences in aphid susceptibility between aphid species and between laboratory bioassays and greenhouse trials. The high initial aphid densities, difficulties to reach the aphids on the undersurface of leaves, stains left by Vertalec on the harvested lettuce, and high cosmetic standards for lettuce mitigated the performance of the insecticides. The potential of using Vertalec, BioNeem, and Safer’s soap for the control of lettuce aphids is discussed in relation to aphid species and crop management.

This study is part of a long-term analysis of nontarget effects of microbial pesticide application in the George Washington (Augusta County, VA, USA) and Monongahela National Forests (Pocahontas County, WV, USA). Ants were collected using pitfall traps to assess the effect of Bacillus thuringiensis Berliner variety kurstaki (Foray 48 F) and gypsy moth nuclear polyhedrosis virus (Gypchek) application on ant communities. Ant samples were also compared by sampling years. Pitfall traps were operated for 45 wk during summers of 1995–1997. A total of 31,732 ants was collected from pitfall traps; they belonged to four subfamilies, 17 genera, and 31 species. The ant species richness, diversity, abundance, and species composition did not change as a result of the treatments. Further tests of ant abundance were suggested because the test power was low. Comparisons between sampling years showed a very similar species composition and species evenness. There was a significant decrease in ant abundance in the third year of sampling, which might have been caused by over-trapping. Some rare species did not appear in the second and third year of sampling.

Field studies were designed to more clearly determine how adult western corn rootworm, Diabrotica virgifera virgifera LeConte, population distribution patterns are altered over time by changes and contrasts in corn (Zea mays L.) plant phenology using whole-plant beetle counts as the sampling tool. In 1994, studies were conducted in a model system consisting of a late-planted corn strip placed in the middle of an early-planted cornfield. The system was replicated over three fields. Large-scale variation was modeled using trend-surface regression analysis to describe the relationship between beetle counts and distance from the center of the late-planted strip. In each field, the beetle distribution became greatly skewed toward the late-planted strip when the strip was either in the tassel or silk stage and the surrounding field was ≥ blister stage. In 1995, studies were conducted in and at the interface of two adjacent cornfields that were planted 9 d apart. Count data were analyzed to quantify population density changes at different sampling locations within and among fields over time as crop phenology changed. Rapid positive or negative changes in beetle densities occurred within and among fields as contrasts in corn phenology changed. In both years, the stability of the beetle distribution was strongly influenced by the length of time that a contrast in plant phenology was maintained between adjacent patches of corn. Directional movements of beetles toward pollinating corn and associated semiochemicals could be inferred from both 1994 and 1995 data analyses. Data suggest that contrasts in crop phenology at the interface and among cornfields should be considered when developing beetle sampling programs and interpreting scouting data to improve the accuracy of rootworm management decisions.

The effect of temperature on the life history of Muscidifurax raptor Girault & Sanders was determined to develop relationships that could be used to improve simulation models of biological control. Immature developmental rates were influenced by temperature and sex. Males developed faster than females, and the developmental rate increased with temperature to 30°C, then declined. Immature survival was lowest at 15 and 33°C, and highest in the range 20–25°C. Sex ratio of emerging parasitoids averaged 72 and 55% from house fly, Musca domestica (L.), and stable fly, Stomoxys calcitrans (L.), pupae and increased with temperature. Female longevity, time to median oviposition, and lifetime progeny production declined as temperature increased. The net reproductive rate was lowest at 15 and 33°C, and greatest at 25°C. Mean generation time decreased with increasing temperature. The intrinsic rate of increase was highest at 30°C. M. raptor has a broad thermal preference which may account for its greater relative abundance and wider seasonal abundance in Alberta compared with other species of naturally occurring parasitoids.

We investigated the survival of Archytas marmoratus (Townsend) from superparasitized Helicoverpa zea (Boddie) larvae. About half of the planidia of A. marmoratus brushed on larvae of the corn earworm, H. zea, became established. Fourth instars were more susceptible to parasitization than other instars, but parasitoid eclosion from superparasitized hosts was greatest in fifth instars. The number of hosts producing A. marmoratus adults declined linearly with the number of maggots per host, with no eclosion of A. marmoratus from hosts with >10 maggots. When third-instar corn earworm were collected from artificially infested, whorl-stage corn after the release of A. marmoratus, 75% of the parasitized larvae were superparasitized. Superparasitism reduced parasitoid eclosion more severely in field plots than in the laboratory. As in laboratory studies, the number of hosts producing A. marmoratus adults declined linearly with an increased number of maggots, but no parasitoid eclosed if hosts had more than four maggots. The number of maggots per corn earworm larva was highly correlated with percentage parasitism. Consequently, the release rate of A. marmoratus might need to be adjusted to host density so that superparasitism does not reduce the survival rate of the parasitoid.

Entomopathogenic nematodes are generally considered beneficial organisms. However, they can affect beneficial insects such as parasitoids. The infectivity of Steinernema carpocapsae (Mexican strain) to Cardiochiles diaphaniae Marsh, a solitary internal wasp parasitoid of melonworm, Diaphania hyalinata (L.), and pickleworm, D. nitidalis (Stoll), was determined under laboratory conditions. S. carpocapsae induced 100% infection in melonworm hosts during exposure periods of 6, 24, 36, and 48 h. The number of nematodes penetrating the host was proportional to the length of exposure period, and the emergence rate of wasp parasitoids was inversely proportional to exposure time. Though only 0–10% of immature C. diaphaniae were parasitized by nematodes within hosts, newly emerged and, to a lesser degree, cocoon-spinning wasp larvae were readily infected by nematodes. In contrast, pupae of C. diapahaniae in completely formed cocoons were resistant to infection. S. carpocapsae adversely affected C. diaphaniae developing in melonworm principally by causing the premature death of the host before the wasp could complete its development. If the wasp larvae were 6 or 7 d old when the melonworm host was parasitized by nematodes, then all the wasp larvae died. However, if the wasp larvae were 8 d old when nematodes parasitized the melonworm, then 39–92% of the melonworms successfully produced wasp parasitoids. Many wasp larvae that emerged from nematode-parasitized melonworms did not form cocoons, and died within 24 h of emergence. However, only a small proportion of the larvae contained nematodes as determined by dissection. The percentage of infected parasitoids and the proportion of emerged parasitoid larvae dying increased as the exposure time to nematodes increased. Overall, S. carpocapsae nematodes are somewhat compatible with parasitoids because they do not kill all parasitoids, and the pupal stage is resistant to infection. However, the direct and indirect mortality of wasps caused by nematodes could result in some interference with biological suppression.

Estimating populations of both pest and natural enemy species is important in the planning and implementation of biological control. For example, synthetic pheromone lures are used to sample bark beetles, and sometimes their predators, in forest ecosystems. However, insect attraction to natural pheromone sources may differ from attraction to synthetic pheromone lures. Moreover, these differences may vary systematically between the target pest and some important natural enemies. Thus, the accuracy of both absolute and relative abundances of bark beetles and predators could vary with lure selection. We evaluated a series of synthetic lures to determine which lure gave the closest approximation to actual numbers of Ips pini (Say) and predators arriving at hosts infested with I. pini in Wisconsin. We deployed synthetic lures containing various ratios of the ( ) and (−) enantiomers of the principal I. pini pheromone component, ipsdienol, with or without an additional component, lanierone. I. pini showed strong preferences for specific enantiomeric ratios of ipsdienol, and these responses were synergized by lanierone. Predators showed equally strong attraction to ipsdienol, but preferred different ratios of the stereoisomers. The addition of lanierone had no effect on predators. The most abundant predator, Thanasimus dubius (F.), showed greater preference for host material infested with I. pini than any synthetic lure. These disparities in responses, combined with strong disparities in seasonal flight patterns, provided estimates of pest to predator ratios that varied by as little as 12% to as much as 12 times, from pest:predator ratios arriving at host material infested with I. pini. These results suggest that variation between herbivores and their natural enemies in their phenology, preferred pheromone blends, and infested host material should be considered when developing estimates of relative pest and predator densities for subsequent management options.

Two pig farms, two dairies, and a combined pig and dairy farm in Denmark were sampled weekly from April to December 1997 to determine the distribution and relative abundance of Musca domestica L. pupal parasitoids. Nine parasitoid species were collected in the study, including Spalangia cameroni Perkins, S. nigripes Curtis, S. subpunctata Förster, S. nigra Latrielle, Muscidifurax raptor Girault & Sanders, Nasonia vitripennis (Walker), Pachycrepoideus vindemiae (Rondani), Urolepis rufipes (Ashmead), and Phygadeuon fumator Gravenhorst. S. nigra had not previously been recorded as a parasitoid on M. domestica pupae in Denmark. Among the five farms, S. cameroni was the most abundant species collected indoors, whereas M. raptor dominated outdoors in the manure heaps. Maximum activity of parasitoids was observed in late summer, which corresponded well with peaks in temperature and fly density. S. cameroni and M. raptor were active from spring to fall, whereas the other species occurred more sporadic and in lower numbers. The overall rate of parasitism was low, ranging from 5.1 to 13.1% among the farms. Spatial distribution of the three most abundant species at indoor sites revealed that M. raptor primarily searches for fly pupae in the illuminated areas of the stable environment, whereas S. cameroni and S. nigripes were randomly distributed.

There has been little research conducted on the effects of native or established predators on populations of the hemlock woolly adelgid, Adelges tsugae Annand. This study used field surveys and cage exclusion experiments to examine the relationship between established predators and A. tsugae in the southeastern United States. Predators were collected in very low densities in both years. Harmonia axyridis Pallas (Coleoptera: Coccinellidae), lacewings (Neuroptera: Chrysopidae and Hemerobiidae), and gall gnats (Diptera: Cecidomyiidae) represented 81% of the total predators collected in 1998. Cage exclusion experiments revealed no significant predator effects in all three sites in 1997 and 1998. It is unlikely that established predators are exhibiting any significant control on adelgid populations because of the low densities of predators that were encountered at a time when adelgids were abundant. Therefore, controlled releases of non-native predators into these sites should be considered.

The entomopathogenic fungus Entomophaga maimaiga causes epizootics in gypsy moth, Lymantria dispar (L.), populations and persists in forests as a reservoir of spores in soil at the bases of trees. To investigate whether E. maimaiga infects Lepidoptera living in leaf litter, we collected and reared larvae in leaf litter, understory vegetation, and on tree boles within a 200-cm radius around trunks of red oak, Quercus rubra L., trees. Among the 358 lepidopteran larvae reared, only one gelechiid larva (out of 84 collected) and one larva of the noctuid Sunira bicolorago (out of 20 individuals from this species) were infected by E. maimaiga. Our collections included 67 gypsy moth larvae, of which 25 (37%) were infected by E. maimaiga. The majority of infected gypsy moth larvae were collected during the second half of June, when few nontarget Lepidoptera were present in the oak leaf litter. A bioassay of Zanclognatha laevigata Grote, a herminiine noctuid whose larvae spend their entire lives in leaf litter, yielded no infection. Because laboratory host specificity studies had demonstrated high levels of infection only in lymantriid larvae, we also caged larvae of the lymantriid Orgyia leucostigma (J. E. Smith) over soil at the bases of trees or in understory vegetation. Levels of infection for O. leucostigma remained consistently lower than among caged gypsy moth larvae, and infection was always higher in the soil than on the understory vegetation. We conclude that, aside from gypsy moth larvae, E. maimaiga infections among litter-dwelling lepidopteran larvae were rare, and we hypothesize that infection of other lymantriids in the field will depend on whether they visit the ground level for a significant period of time.

Mass-trapping using semiochemical lures is a potentially useful control measure against bark beetle pests. A serious problem, however, is the inadvertent removal of predators that respond to these baits as kairomones. Ips pini (Say) infests hard pines in the western, Great Lakes, and eastern forests of North America. In Wisconsin, I. pini responds primarily to 50( )/50(−) and 75( )/25(−) blends of ipsdienol, its principal pheromone component. Its response is increased by a synergist, lanierone. Its most abundant predators in Wisconsin include Thanasimus dubius (F.), which responds to similar blends of ipsdienol, and Platysoma cylindrica (Paykull) and P. parallelum (Say), which respond to primarily (−) enantiomers of ipsdienol. These predators do not show increased response when lanierone is released in addition to ipsdienol. We conducted a no-choice assay using rotating blends of ipsdienol and lanierone to simulate a trap-out treatment. Lures that contain enantiomers of ipsdienol most preferred by I. pini, in combination with lanierone, can selectively remove up to three to six times more pests than predators during the spring. Moreover, delaying deployment of the same lures until summer can result in removal of up to 39 times more pests than predators. In contrast, lures that contain enantiomers of ipsdienol most preferred by predators can inadvertently remove two or more predators per each bark beetle trapped. Exploiting these behavioral differences between pests and predators can improve biological control by conserving predators during trap-out programs.

The browntail moth, Euproctis chrysorrhoea (L.), is periodically a major urban pest in the southern United Kingdom. High populations cause severe defoliation of a range of host plants, often in urban areas; and urticating hairs of larvae are highly irritating to humans. Control of outbreak populations is therefore desired. As an alternative to chemical insecticide sprays and labor intensive nest removal, nucleopolyhedrovirus (NPV) has been considered as a biological control. To evaluate if use of this spray would affect other lepidopterans we carried out detailed host range testing using a number of wild-caught lepidopteran species. Seventy-three species of Lepidoptera from 14 families, including four species of Lymantriidae and two species of hymenopteran sawfly, were found to be nonpermissive to E. chrysorrhoea NPV at a dose of 10⁶ occlusion bodies per second instar. Some individuals from 11 species of Lepidoptera and one hymenopteran sawfly died of baculovirus infection, but none of these were shown, by dot blot analysis of DNA, to be infected with E. chrysorrhoea NPV. In two of these species, uninfected control larvae also died of infection, indicating that they carried an overt infection in the field. However, in eight species of Lepidoptera and one sawfly, there were no control deaths, providing possible evidence that an inapparent or latent infection had been stressed out of the wild-caught insects by inoculation with a high dose of E. chrysorrhoea NPV. Our results suggest this NPV may be monospecific, and that it is unlikely to present a risk to any nontarget species. These characteristics make it highly suitable for use as a bioinsecticide, particularly in urban areas and nature reserves.