Unexplained variation in the relationship between herbivore densities and the short-term appearance of crop damage is sometimes observed in pest management. Here we used a field survey of commercial cotton fields and a linked questionnaire for cooperating pest control advisors to document the existence of such unexplained variation in the impact of the western tarnished plant bug, Lygus hesperus, on upland cotton, Gossypium hirsutum. L. hesperus feeds preferentially on flower buds (“squares”), and the plant may respond to this damage with abscission of the square. We explored four classes of factors that might contribute to unexplained variation in square abscission. First, misperceptions by the human observer (i.e., sampling problems) may play a role, because commercial field scouts significantly underestimate densities of L. hesperus nymphs. Second, we found no support for the hypothesis that variable behavior expressed by L. hesperus contributes to unexplained variation in square abscission. L. hesperus seems to generate relatively predictable levels of square feeding damage; the variation that was observed was unrelated to grower categorization of fields as exhibiting normal versus unexpectedly high or low levels of square abscission. Third, variable plant responses to damage may instead be the key source of unexplained square abscission. Younger plants and plants with higher petiole phosphate concentrations expressed increased sensitivity to L. hesperus feeding; these correlations must, however, be tested experimentally before definitive conclusions are drawn. Fourth, another arthropod might be generating damage that was erroneously being attributed to L. hesperus. The omnivore Geocoris pallens was a candidate agent of cryptic damage to squares; however, an experiment showed that G. pallens generated only trivial square damage and no detectable increase in square abscission. Thus, this study has focused our attention away from the arthropod side of the interaction and toward the host plant as the primary source of greater than expected square abscission generated by L. hesperus.

Biting midges of the Nearctic Culicoides variipennis complex, C. sonorensis Wirth and Jones, C. variipennis (Coquillette), and C. occidentalis Wirth and Jones, are widespread and locally abundant throughout the United States. An understanding of environmental factors associated with the distributions of respective species is of value because risk for bluetongue disease in livestock is defined by the distribution of C. sonorensis, the primary vector of bluetongue viruses in the United States. This study tested the relationship between dissolved salts and immature populations of the C. variipennis complex by examining widespread and diverse aquatic habitats with larval populations and using discriminant analysis to classify larval habitats by species on the basis of soil chemistry. Aquatic habitats with immature C. sonorensis in British Columbia, Illinois, New Mexico, and Washington were moderate-high in levels of dissolved salts, as is typical for habitats with this species. In contrast, a nearby site with the sister species C. variipennis in British Columbia, as well as aquatic habitats in Illinois, were low in dissolved salts, similar to habitats with this species in the eastern United States. A saline stream in central Washington with C. occidentalis was extremely high in dissolved salts, like the playa lakes where this species occurs in the far western United States, whereas a stock pond near the saline stream was lower in dissolved salts and occupied by C. sonorensis. These data confirm that conspecific populations of the C. variipennis complex occur in habitats that have similar levels of dissolved salts, which differ between species, regardless of geographic location. Reverse stepwise discriminant analysis using new and archived soil chemistry data showed that electrical conductivity and chloride discriminated best between habitats with C. variipennis or C. sonorensis and that the combination of electrical conductivity and calcium had the most power of discrimination between habitats with C. sonorensis or C. occidentalis. Collectively, these findings represent convincing evidence that levels of dissolved salts influence the suitability of aquatic habitats for immature populations the C. variipennis complex and hence in part determine respective species’ distributions.

Accurate timing of pest control measures requires a good understanding of the emergence pattern of the specific pest populations. In 1999–2000, pupae of the cabbage maggot, Delia radicum L., and the turnip maggot, D. floralis Fallén, were collected in the autumn from nine widespread locations in Norway (58–70° N). After diapause development during winter, emergence was studied in a climate chamber at 18°C. The time to 50% emergence was <2 wk for all populations of D. radicum, and the emergence period (time elapsed between 10 and 90% emergence) was ~4 d on average. The results indicated uniform and early emerging populations of this species. D. floralis, however, had much later emergence, with a wide range of emerging biotypes. The time to 50% emergence of D. floralis varied from 5 to 10 wk between populations. Moreover, the emergence period varied between 2 and 7 wk for the different populations, indicating mixtures of differently emerging biotypes. The ecological basis for the diverging emergence patterns is discussed.

Seasonal flight activity periods and emergence phenologies of the cabbage maggot, Delia radicum L., and the seedcorn maggot, Delia platura (Meigen), were studied from 2002 to 2004 in canola, Brassica rapa L. and Brassica napus L., in central Alberta, Canada, in relation to degree-days and Julian-days. D. radicum was univoltine in canola. Peak emergence occurred after an accumulation of 345.8 ± 79.4 DD, and 50% flight activity required accumulation of 324.5 ± 46.8 DD (soil base 4°C). D. platura was bivoltine in canola. Peak emergence of the first generation required 339.5 DD, and the second generation required 594.5 ± 38.9 DD (soil base 3.9°C). Peak flight activity occurred after accumulation of 255.0 ± 74.2 and 639.9 ± 69.4 DD for the first and second generations, respectively. A logistic model was used to describe the relationship of degree-days and Julian-days with emergence patterns of adult flies and predicted that 10, 50, and 95% emergence of D. radicum required 213.7 ± 39.9, 324.5 ± 46.8, and 467.2 ± 46.3 DD, respectively. Logistic analysis predicted that 50% emergence of the first generation of D. platura required an average of 255.0 ± 74.2 DD, and the second generation required 526.8 ± 66.6, 639.9 ± 69.4, and 952.8 ± 77.0 DD for 10, 50, and 95% emergence, respectively. Determination of the temporal patterns of abundance of D. radicum and D. platura has potential application for pest management because it can help ensure that phenologies of candidate agents for biocontrol are synchronous with those of the pests they are targeted to control.

The development, fecundity, and life table parameters of Gonatocerus ashmeadi Girault, an egg parasitoid of the glassy-winged sharpshooter, Homalodisca coagulata (Say), were studied in the laboratory at six constant temperatures between 12 and 32°C. At 12°C, the parasitoid failed to develop beyond the third instar, and durations of the egg stage and the first and second instars were prolonged. Development from the egg stage to adult emergence varied from 27.1 d at 16°C to 9.5 d at 28°C. Temperature thresholds for development ranged from 3.8°C for first-instar larvae to 12.8°C for the pupal stage. The thermal constants were lowest for the second-instar larvae (26.7 DD) and highest for the pupae (75.4 DD). Nearly 207 DD were required above the lower temperature threshold of 8.5°C to complete development from egg to adult. The optimum temperature for egg to adult development was 29.2°C. Survival from egg to adult was 67.4% at 16°C and ranged from 83.4 to 86.7% between 20 and 32°C. At 16–32°C, the population had a type I survivorship pattern. At 16°C, longevity of adult females and males averaged 27.1 and 19.0 d, respectively, but declined to 6.4 and 6.9 d at 32°C. At 20–32°C, peak adult emergence occurred on the first day of emergence, but at 16°C, it was greatest on the second day. When exposed to temperatures ranging from 16 to 32°C, the female:male sex ratio was similar, ranging from 3.4 to 5.6. Lifetime fecundity was greatest at 24°C and lowest at 32°C, with the maximum net reproduction also occurring at 24°C. Greatest intrinsic and finite rates of increase, shortest population doubling time, and mean generation time occurred when G. ashmeadi was held at 28°C. The parameters defined in this study can influence geographical distribution and are important for the mass-rearing this wasp as biological control agent for the glassy-winged sharpshooter.

Anagyrus sp. nov. nr. sinope Noyes and Menezes (Hymenoptera: Encyrtidae) is a new parasitoid of the Madeira mealybug, Phenacoccus madeirensis Green (Hemiptera: Pseudococcidae), a common pest in the greenhouses of the southeastern United States. The objectives of this study were to assess the influence of temperature (15, 20, 25, 30, and 35°C) and mating status (virgin and mated) on the life history of this parasitoid. Anagyrus sp. nov. nr. sinope is an arrhenotokous parasitoid with the mated females producing progeny with the proportion of males between 0.34 and 0.41. Parasitism rates ranged between 17 and 40% and increased with temperature. The number of progeny produced by the mated parasitoids increased from 8 at 15°C to 11 at 30°C, which were 10 and 50% lower, respectively, than that of virgin parasitoids. For females of either mating status, brood sizes averaged between 3.1 and 4.9 progeny per mummy. More than 94% of parasitoids successfully survived to adulthood between 15 and 30°C. No parasitoid completed development at 35°C. The developmental times of Anagyrus sp. nov. nr. sinope were 55, 25, 17, and 12 d at 15, 20, 25, and 30°C, respectively. Using a linear thermal summation model and a nonlinear Logan 6 model, we determined that the lower developmental threshold, upper developmental threshold, and optimal temperature to be 11.1, 35.0, and 30.3°C, respectively, and the thermal constant was 222.2 DD. The lifetime fecundity of Anagyrus sp. nov. nr. sinope were 58–71 progeny between 15 and 30°C. Mated females had significantly higher lifetime fecundity than virgin females. We expect Anagyrus sp. nov. nr. sinope to survive and reproduce within a temperature range commonly maintained in greenhouses.

Anagyrus sp. nov. nr. sinope Noyes and Menezes (Hymenoptera: Encyrtidae) is a candidate for biological control of the Madeira mealybug, Phenacoccus madeirensis Green (Hemiptera: Pseudococcidae). P. madeirensis is a serious pest of horticultural crops in the southeastern United States. The first experiment studied the effect of temperature (15, 20, 25, 30, and 35°C) and feeding treatment (starved, hydrated with distilled water, and nourished and hydrated with diluted honey) on adult longevity of Anagyrus sp. nov. nr. sinope. Nourished and hydrated female parasitoids survived an average of 52.8 d at 15°C, which was 14 and 8 times longer than starved and hydrated females at the same temperature, respectively, and 8 times longer than nourished and hydrated females at 35°C. The second experiment studied the influence of feeding treatment on the reproduction of Anagyrus sp. nov. nr. sinope at 25°C. Nourished and hydrated female parasitoids lived (mean = 14.2 d) and reproduced (mean = 7 d) for a longer duration, parasitized more hosts (mean = 16), and produced more offspring (mean = 45) than starved or hydrated females. The third experiment assessed the longevity and reproduction of Anagyrus sp. nov. nr. sinope after storage for various durations (0, 1, 4, 7, 14, 21 d) at 15 and 25°C. Parasitoids stored at 15°C had increased longevity and a decreased reproductive period but similar parasitism rates and fecundity to those stored at 25°C. The results suggested that the parasitoids could be stored at 15 and 25°C for up to 14 d without significant reduction in fecundity after release.

The development period of immature stages of the green apple aphid, Aphis pomi (De Geer) (Homoptera: Aphididae), at six constant temperature regimens (20, 24, 28, 30, 32, and 34°C) was modeled to determine mathematical functions for simulating aphid development. Ten models (one linear and nine nonlinear) were used to describe the relationships between temperature and development rate of the different instars and stages of A. pomi (DeGeer) at constant temperatures. All models (except logistic and linear) provided accurate values for the optimum temperature for the first-, second-, third-, and fourth-instar larvae and for total development. The results suggest that, among four models (Hilbert and Logan, Lactin, Briere, and Analytis) that estimate all three parameters (t_min, t_opt, t_max), Lactin and Hilbert and Logan models gave the most suitable fit of data.

The effect of cold storage and photoperiod on diapause termination of the predatory mite Euseius finlandicus was studied under laboratory conditions. Females in diapause that developed under a short-day photoperiod of L:D 8:16 h and 20°C were exposed for 1–13 wk to 5°C and subsequently maintained under L:D 8:16 h and 20°C, after which the percentage of females terminating diapause was recorded. After 1–4 wk at 5°C, the number of days required for diapause termination in 50% of females (TA₅₀) was similar to that of the control mites maintained continuously at L:D 8:16 h and 20°C. This indicates that cold is not a prerequisite for the completion of diapause development. Furthermore, when mites were maintained for longer periods (7, 10, or 13 wk) at 5°C, TA₅₀ was significantly longer than in the control mites. This may indicate an adverse effect of cold storage on the completion of diapause development or on postdiapause development. However, the longer exposures to cold resulted in synchronous diapause termination. When diapause females were maintained under a series of different photoperiods and 20°C without previous cold exposure, diapause was terminated rapidly under the photoperiods of L:D 16:8, 14:10, and 13:11 h. In contrast, under the shorter-day photoperiods of LD 8:16, 10:14, and 12:12 h, diapause was maintained and eventually ended spontaneously after a long period of time. These results may be useful for the long-term storage of this predatory mite, which could be required for use in biological control programs.

Postdiapause larval development and adult emergence of the wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), were studied in three field populations collected at Amsterdam, Conrad, and Opheim, MT, at 10, 15, 20, 25, 30, and 35°C and at 43, 54–62, and 75–76% RH under laboratory conditions. No development beyond the larval stage occurred at either 10 or 35°C at any relative humidity. At 10°C, >75% of the larvae remained alive, but quiescent, whereas at 35°C, ≈50% of the larvae probably re-entered diapause. Temperature and population were the main factors affecting development time and adult emergence. The shortest development times occurred at temperatures of 20°C and higher, but development time increased sharply at 15°C. Adult emergence was highest at 20 and 25°C for the two populations collected at Amsterdam and Conrad (western Montana) and was highest at 15 and 20°C for the population collected at Opheim (eastern Montana). Emerged females were twice as heavy as males. Temperature and relative humidity did not affect weight, but emerged adults from the populations collected at Amsterdam and Conrad were heavier than adults emerged from the population collected at Opheim. Sex ratio of emerging adults was female biased and was strongly affected by population. The optimal conditions for larval–adult development of C. cinctus lie between 20 and 25°C and 60–75% RH. This data will be used to predict adult emergence and forecast the onset of the adult flight period in Montana wheat fields.

The red turpentine beetle, Dendroctonus valens LeConte (Coleoptera: Curculionidae: Scolytinae), is a serious, exotic pest of pines in China that was introduced from North America during the 1980s. Relatively little is known of its pheromone biology. In our studies, gas chromatographic and mass spectral (GC-MS) analysis of hindgut volatiles revealed the presence of trans-verbenol, cis-verbenol, myrtenol, myrtenal, and verbenone, which are frequently reported pheromone compenents of Dendroctonus spp. Subsequently, bioactivity trials were conducted in the laboratory and field for three oxygenated monoterpenes: trans-verbenol, myrtenol, and myrtenal. Electroantennogram tests indicated that D. valens possess olfactory sensitivity for these three compounds. Additionally, walking D. valens displayed anemotaxis toward all three compounds in a Y-tube olfactometer. In field tests, both trans-verbenol and myrtenol significantly increased catches of beetles in traps baited with host kairomone [a blend of three host monoterpenes: ( )-α-pinene, (−)-β-pinene and ( )-3-carene]. These conspecific-produced attractants may have a role in D. valens chemical communication. Although the appropriateness of classifying these compounds as pheromones is still uncertain, these compounds clearly have potential for use in management of this serious pest.

European corn borer females Ostrinia nubilalis Hübner (Lepidoptera, Pyralidae) exhibited upwind flight to three main host plants, corn Zea mays, hemp Cannabis sativa and hop Humulus lupulus, in a laboratory wind tunnel. Within a 15-min experimental period, 22.9% to 24.3% mated females flew toward and landed on a single potted corn plant. A potted hemp plant attracted 25.7% females. In a choice test, significantly more females landed on a hemp plant than on an adjacent corn plant. In contrast, paprika Capsicum annuum did not elicit attraction. Headspace collections from corn, hemp, and hop contained 18 compounds which consistently elicited a response from female antennae. Four of these, (Z)-3-hexenyl acetate, β-caryophyllene, (E)-β-farnesene, and (E,E)-α-farnesene co-occurred in three host plants studied. A 4-component blend of these compounds did not attract female moths in the wind tunnel. Availability of a wind tunnel bioassay is, however, a step toward the identification of plant volatiles guiding long-range attraction of gravid corn borer females.

We studied the spatial distribution of Locusta migratoria manilensis (Meyen) egg pods by integrating geostatistical analysis and a geographic information system (GIS) techniques. During 2 yr of extensive surveys, egg pod data were collected over two spatial scales: 292 regularly grids with 450-m intervals over the entire study area (6,000 ha), and 2,601 regularly grids of 0.5-m separation in potential oviposition areas located on the slopes, damaged by the locust plague or covered with sparse vegetation. Ecological variables included vegetation cover, topography (aspect and slope), and soil parameters (salinity, pH, moisture at 5 cm, organic matter). Results showed that most egg pods (66.27 and 72.24% for 2002 and 2003, respectively) were found on south-facing and southwest-facing slopes with sparse reed cover (0 ≈ 30%), low soil salinity (<2.0%), and suitable soil moisture at 5 cm (10.1 ≈ 20.0%). t-Tests indicated that sites between with egg pods and without egg pods were significantly different in vegetation cover, sun index (combination of aspect and slope), soil moisture at 5 cm depth, and salinity. Semivariograms showed spatial autocorrelation in egg pod distribution at distances ranging from 0.5 to 452 m. The spatial distribution of egg pods was best described using spherical models. GIS risk assessment maps, derived by block kriging, displayed the probabilities of occurrence of the locust egg pods at an area-wide scale. The results may provide useful information on planning for site-specific pest management. Targeted monitoring and spraying can be effectively used during the peak hatch in the following spring.

Density-dependent melanism, i.e., the phenomenon that individuals at high population densities develop into a dark-colored phenotype, is often explained as a defense against density-dependent responses of natural enemies, in particular, disease organisms. In the work reported here, we wanted to test whether density-dependent melanism in insects may yield protection against parasitoids, which are important regulators of many outbreak populations. This was carried out by collecting comprehensive field data on parasitoid attack rates and overall mortality of both larvae and pupae of the outbreak species Operophtera brumata L. (winter moth) in relation to degree of cuticular melanism. As expected, the results showed that parasitoids were the dominating mortality factor, but unexpectedly, parasitoid attack was positively associated with the degree of melanism. Also, mortality caused by unknown factors seemed to be highest in melanic larvae. These results indicate that density-dependent melanism, which is known to protect several species of insects against disease agents, does not confer protection against parasitoids in this outbreak species, which is largely regulated by parasitoids in nature.

Delphacodes kuscheli (Hemiptera: Delphacidae) is the vector of maize rough dwarf virus that affects maize production in the central region of Argentina. The spatial abundance pattern and body morphology of the insect vector were studied during the spring and summer of 1999 and 2000 in endemic and nonendemic areas affected by this virus. An estimation of insect density was obtained from high sticky traps (6 m high) placed at nine sampling sites along a 500-km transect that crossed the main maize production area in Argentina. Host patches were detected, and their areas were measured using Landsat 5 Thematic Mapper (TM) imagery from the region to be studied. Population phenology of the individuals collected in the sampling sites was compared using multivariate analysis of morphometric variables. The land use estimated from Landsat 5 TM images varied according to the different sites and years. Areas with similar proportion of winter pastures, winter cereals, and perennial pastures were grouped together by complete linkage cluster analysis. The mean abundance of the vector varied and did not show a consistent pattern. The highest abundances were not found in the traps placed in the endemic region. Multiple linear regression of the proportion of area (arcsine transformed) covered by annual pastures, perennial pastures, and winter crops versus mean abundance of D. kuscheli (expressed as insect/trap/d) were significant for both years (R² = 0.91 for 1999 and R² = 0.82 for 2000). The function that related insect abundance and host area was different each year; this suggested that other factors were affecting the “insect productivity” of a certain host area. There were clear morphometric differences among the individuals collected in the different sampling sites, although the sites were not so far away from one another (50 km). When comparing the phenotypes of the insects collected in different sites, 55 (1999) and 51% (2000) of the cases were correctly assigned to the sites from which the individuals were collected. These percentages increased to 74 and 62% if the individuals were grouped according to the cluster of land use obtained from Landsat 5 TM images. In all cases, Wilk’s lambdas were highly significant. The role of the distribution, abundance, and quality of the host plants is analyzed in this study.

Thrips exhibit different reproductive modes including thelytoky (females produced from unfertilized eggs), arrhenotoky (males produced from unfertilized eggs and females produced from fertilized eggs) and deuterotoky (females and males produced from unfertilized eggs). We investigated patterns of reproductive modes in onion thrips, Thrips tabaci Lindeman, populations and potential effects of the bacterium Wolbachia and temperature on these modes. We also examined the possibility that male-producing T. tabaci populations were resistant to the frequently used insecticides, lambda-cyhalothrin and methomyl. In New York during 2002–2004, T. tabaci populations were sampled from 20 onion fields and reproductive mode was determined by identifying sex of progeny from virgins. Half of the populations were thelytokous and half were a mix of thelytokous, arrhenotokous and deuterotokous individuals, which we refer to as a male-producing population. In two of four cases, the reproductive mode of a population from the same onion field changed across years, suggesting that populations either mix or an external factor caused the change. To address the latter, we speculated that Wolbachia or high temperature mediated reproductive modes. Samples of T. tabaci representing each reproductive mode were examined for Wolbachia using diagnostic polymerase chain reaction (PCR), but it was not detected. Cytological examination of ovaries from two additional thelytokous lines also showed no evidence of Wolbachia. Similarly, high temperature did not affect sex allocation ratios in either thelytokous or male-producing populations. Male-producing T. tabaci populations were not positively correlated with resistance to lambda-cyhalothrin, or tolerance to methomyl. The role of the different reproductive modes in T. tabaci populations in onion fields remains unclear.

We analyzed published field data concerning western corn rootworm (Diabrotica virgifera virgifera LeConte) and northern corn rootworm (Diabrotica barberi Smith and Lawrence) survival from egg to adult to create general relationships between density and survival. A series of equations were generated that best fit the data, and these equations may be used to help understand density-dependent survival in future studies. In general, the datasets showed a decline in the proportion surviving to adulthood as egg density increased. The survival of northern corn rootworm was lower than that of western corn rootworm. Data for both natural and mechanical infestations of soil with eggs show decreasing proportion surviving as density increases. Several nonlinear equations fit the data for both species very well. Density-dependent survival can account for differences in observations of insecticide survival at different initial western corn rootworm densities.

Wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), oviposition patterns and larval development in downy brome grass, Bromus tectorum L., and wheat, Triticum aestivum L., were compared in a commercially grown wheat field infested with downy brome grass in Montana. Seven weekly randomly selected samples of stems for each plant species were collected at points where both plants were growing together. The level of infestation in downy brome grass was almost two-fold higher than for wheat throughout the growing season. Larval mortality was not detected in either plant species early in the season, but mortality was more frequent in downy brome grass as the host plants matured. Mortality of late-instar larvae late in the season was significantly higher in mature downy brome grass than in mature wheat stems. The weight of these late-instar larvae from wheat was almost four-fold heavier than larvae from downy brome grass. Stem height and seed weight in wheat were significantly reduced by larval sawflies feeding. In contrast, stem height, stem diameter, seed weight, and seed number in grass stems were significantly greater in infested downy brome grass stems compared with uninfested plants. Our results suggest that downy brome grass, a serious weed in wheat cropping, may play an important role in the survival and dynamics of wheat stem sawfly populations in the northern Great Plains.

Ichneumonoidea is an important group in terrestrial ecosystems, although its community structure in tropical agricultural environments is unknown. Consequently, a characterization of ichneumonoid communities was done in an agricultural environment consisting of a cultivated area with and without surrounding vegetation in the state of Yucatan, Mexico. The characterization helped to understand how Ichneumonoidea diversity changes in the vegetation structure adjacent a crop. Three sampling sites were established: nine experimental plots in open area with continual agricultural use without surrounding vegetation (NSV), nine experimental plots with surrounding vegetation in a remaining patch (WSV), and nine plots inside of secondary vegetation of a remaining 7-yr-old patch (SV). Ichneumonoidea specimens were collected with Malaise and yellow pan traps. A total of 1,715 specimens were collected, divided into 40 subfamilies, resulting in 138 genera and 480 species. Of these, Braconidae accounted for 1,115 specimens from 21 subfamilies, 84 genera, and 342 species, whereas Ichneumonidae was represented by 600 individuals from 19 subfamilies with 54 genera and 142 species. Braconidae had higher species richness, abundance, and diversity than Ichneumonidae. Both families exhibited higher diversity in the treatment with surrounding vegetation. Koinobiont species were most common in both families. We suggest that vegetation structure and spatial distribution seem to have greater effect on community structure. Our results suggest that Ichneumonoidea could be a better indicator of the degree of disturbance than of environmental preservation.

To study the potential competitive risk of the introduced Chrysoperla carnea (Stephens) on the indigenous trash-carrying chrysopid Mallada desjardinsi (Navás), we studied the occurrence of cannibalism and intraguild predation (IGP) at different prey densities. In C. carnea, 100% cannibalism was observed in the absence of aphids. In M. desjardinsi, cannibalism was also observed, but absence of cannibalism occurred at 35% in pairs of second- third-instar larvae and at 70% in pairs of third- third-instar larvae. In pairs of M. desjardinsi larvae whose trash package had been artificially removed, all third-instar larvae ate second-instar larvae. The trash package may play a role in the reduced mortality of younger larvae by cannibalism. IGP occurred in all pairs. In the absence of aphids, the interaction was symmetric between second-instar larvae, but asymmetric for second- versus third- and third- versus third-instar larvae, and the interaction was similar when M. desjardinsi larvae with or without trash package were paired with C. carnea larvae. When third-instar larvae of both species were paired, C. carnea larvae ate significantly greater numbers of M. desjardinsi larvae than vice versa. The trash package of M. desjardinsi larvae may thus not play a defensive role against IGP by C. carnea. Increasing the availability of aphids tended to decrease both cannibalism and IGP levels. Nontarget effects such as competitive displacement resulting in loss of potentially beneficial attributes of the indigenous M. desjardinsi by the exotic C. carnea are likely to be negligible under conditions of abundant aphids.

Ground beetle assemblages were compared in organic, no-till, and chisel-till cropping systems of the USDA Farming Systems Project in Maryland. The cropping systems consisted of 3-yr rotations of corn (Zea mays L.), soybean (Glycine max L. Merr.), and wheat (Triticum aestivum L.) that were planted to corn and soybean during the 2 yr of field sampling (2001–2002). Each year, ground beetles were sampled using pitfall traps during three 9- to 14-d periods corresponding to spring, summer, and fall. A total of 2,313 specimens, representing 31 species, were collected over the 2 yr of sampling. The eight most common species represented 87% of the total specimens collected and included Scarites quadriceps Chaudoir, Elaphropus anceps (LeConte), Bembidion rapidum (LeConte), Harpalus pensylvanicus (DeGeer), Poecilus chalcites (Say), Clivina impressefrons LeConte, Agonum punctiforme (Say), and Amara aenea (DeGeer). Canonical variates analysis based on the 10 most abundant species showed that the carabid assemblages in the three cropping systems were distinguishable from each other. The organic system was found to be more different from the no-till and chisel-till systems than these two systems were from each other. In 2002, ground beetle relative abundance, measured species richness, and species diversity were greater in the organic than in the chisel-till system. Similar trends were found in 2001, but no significant differences were found in these measurements. Relatively few differences were found between the no-till and chisel-till systems. The estimated species richness of ground beetles based on several common estimators did not show differences among the three cropping systems. The potential use of ground beetles as ecological indicators is discussed.

After causing substantial mortality in the northeastern and mid-Atlantic United States, the hemlock woolly adelgid, Adelges tsugae Annand (Homoptera: Adelgidae), has recently invaded the southern Appalachian region. Although general estimates of regional spread exist, the landscape-level dynamics of A. tsugae invasion are poorly understood—particularly factors predicting where the pest is likely to first infest a landscape. We examined first-year infestation locations from Great Smoky Mountains National Park and the Blue Ridge Parkway to identify possible factors. For 84 infested and 67 uninfested sites, we calculated values for a suite of variables using a geographic information system. After identifying significant variables, we applied four statistical techniques—discriminant analysis, k-nearest neighbor analysis, logistic regression, and decision trees—to derive classification functions separating the infested and uninfested groups. We used the resulting functions to generate maps of A. tsugae infestation risk in the Great Smoky Mountains. Three proximity variables (distance to the closest stream, trail, and road) appeared in all four classification functions, which performed well in terms of error rate. Discriminant analysis was the most accurate and efficient technique, but logistic regression best balanced accuracy, efficiency, and ease of use. Our results suggest that roads, major trails, and riparian corridors provide connectivity enabling long-distance dispersal of A. tsugae, probably by humans or birds. The derived classification functions can yield A. tsugae infestation risk maps for elsewhere in the southern Appalachian region, allowing forest managers to better target control efforts.

Structural complexity may affect activity and abundance of ground-dwelling arthropods. In this field experiment, the short-term effect on abundance of ground-active carabid beetles (Coleoptera: Carabidae) and lycosid spiders (Araneae: Lycosidae) from slash (logging residue) on the ground was studied. Arthropods were collected by pitfall trapping in three clear-cuts in southwest Sweden. The distribution of slash on the ground was manipulated, and two types of microhabitats were created adjacent to traps, i.e., either slash was cleared (bare ground traps) or slash was aggregated in heaps (slash-covered traps). Overall, carabids were significantly less abundant on the bare ground compared with the slash covered ground. For lycosids, no difference in abundance between the two microhabitat types was found. In reference plots, where no manipulation of microhabitat complexity was carried out, an overall positive relationship between structural complexity (slash height) and abundance of carabids was found. For lycosids, however, no correlations in reference plots were found. Bare ground microhabitats are mimicking structural complexity in clear-cuts after commercial slash harvest for biofuel. Large-scale removal of structural elements in clear-cuts might have short-term local effects, such as altered composition of arthropod communities.

Coleomegilla maculata (DeGeer), which is a frequent predator of Helicoverpa zea (Boddie) eggs on sweet corn, prefers to oviposit on plants that have glandular trichomes. These plants provide C. maculata eggs a refuge from cannibalism and other predation. Previous work showed that interplanting glandular pubescent weeds in corn increases C. maculata density and predation on H. zea eggs. We conducted an oviposition preference screening to identify a cultivated species that could provide the same augmentation of C. maculata and possibly increase biological control. In our experiment, tomato had 2.5 times more C. maculata eggs found on it than Acalypha ostryifolia Ridell, a weed documented to be preferred for oviposition over corn. In a separate experiment, 9.6 times more C. maculata eggs were found on a tomato companion crop than on corn, and eggs on tomato had 2.6–5.9 times higher survival than those on corn. In corn plots with a companion crop of tomato, C. maculata larvae were 5–10 times more abundant near the companion crop than in an equivalent location in the corn monoculture. Augmentation of larval densities declined as distance from the companion tomato crop increased, but the augmentation effect persisted for at least 5 m away from the companion crop. In 1 yr of our study, there was a trend toward higher densities of C. maculata adults in the plots with a companion crop of tomato. The observed augmentation of C. maculata did not result in an increase in H. zea egg predation or decrease in ear infestation.

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), has recently invaded North America from Asia and has become a major pest in soybean. Using field surveys and cage exclusion techniques, we identified the effect of natural enemies and abiotic factors on the growth of soybean aphid populations in 2004 and 2005. The soybean aphid population was significantly limited by natural enemies in the field. Generalist predators dominated the natural enemy community. One species, Orius insidiosus Say (Hemiptera: Anthocoridae) represented 85–90% of predators found. There was a significant negative relationship between aphid population growth and O. insidiosus abundance. For other predators, there were no relationships between abundance and aphid population growth. The spatial distribution of aphids among plants affected the impact of O. insidiosus on aphid population growth. When aphids were distributed in a clumped manner, increases in O. insidiosus numbers resulted in lower aphid growth rates. For randomly distributed aphids, there was no effect of O. insidiosus abundance on aphid population growth. Finally, we found no relationship between aphid population growth and degree-day accumulations. The potential of O. insidiosus to suppress soybean aphid population growth at low aphid numbers and the importance of the predator to soybean aphid integrated pest management are discussed.

The diamondback moth Plutella xylostella L. (Lepidoptera: Plutellidae) is known to be an oligophagous pest on crucifers. Recently, a population of diamondback moths was found to infest sugar snap and snowpea in the Rift Valley in Kenya, causing heavy damage. The effect of resident parasitoids on diamondback moths in snowpea (Pisum sativum L.) was studied in the field. In addition, parasitism of diamondback moths by the newly introduced parasitoid Diadegma semiclausum (Hellen) was evaluated. Snowpea provided an enemy-free space for diamondback moths. Local parasitoids attacked diamondback moths only sporadically and in very low numbers (mean of 0.25 individuals/20 plants during the first study period) on diamondback moths on pea compared with a mean of 15.4 individuals/20 plants on kale (Brassica oleracea acephala L.) However, diamondback moth density was higher on kale (mean of 61.1 larvae/20 plants) than on snowpea (mean of 11.4 larvae/20 plants). Differential diamondback moth infestation and level of parasitism might have been affected by a fungal infection (Ascochyta) of the pea plants. In both crops, the most abundant parasitoid was Oomyzus sokolowskii Kurdjumov. After the release of D. semiclausum, the number of diamondback moths in kale decreased drastically to <2 individuals/20 plants; however, the parasitoid had little effect on diamondback moths on snowpea. Percentage parasitism on snowpea increased from 2.3 to 4%, whereas on kale, it increased from 25.6 to 75.7%. A host plant expansion could be of future advantage for the diamondback moth to avoid higher enemy pressure caused by D. semiclausum.

The exploration for the fire ant diseases Vairimorpha invictae Jouvenaz and Ellis (Microsporidia: Burenellidae) and Thelohania solenopsae Knell, Allen, and Hazard (Microsporidia: Thelohaniidae) was conducted from 2001 to 2005 in Argentina, Paraguay, Chile, Bolivia, and Brazil. A total of 2,064 colonies were sampled from 262 sites. Three sites with high prevalence of pathogens were monitored periodically for the persistence of the infections. V. invictae occurred at 12% of the sites and in 10% of the colonies. Except for one infected colony in Bolivia, its distribution was restricted to the eastern part of the region surveyed. The highest occurrence was in Santa Fe Province. T. solenopsae presented a much wider distribution. It occurred at 25% of the sites and in 13% of the colonies. The highest occurrence was in Buenos Aires Province. This is the first report of T. solenopsae in the northwest, in the west, in central Argentina, and in Bolivia, and infecting S. interrupta (Santschi). Simultaneous infections were found at 4% of the sites and in 2.2% of the colonies. The periodical examination revealed high infection levels in most occasions. The prevalence of T. solenopsae ranged from 10 to 90% of the colonies, V. invictae from 0 to 60%, and dual infections from 0 to 50%. Each microsporidium exhibited a characteristic enzootic/epizootic wave. Successive epizootic levels observed in both infections provide a more constant pressure against fire ant populations. These diseases are promising classical biological control agents of the imported fire ants in the United States.

A laboratory colony of Ceratapion basicorne (Illiger) was established from adults reared from infested plants of yellow starthistle, Centaurea solstitialis L. (Asteraceae), that were collected in eastern Turkey. Newly emerged adults fed on yellow starthistle foliage and mated, but females did not oviposit. The feeding rate of females decreased to almost zero by 16 d after emergence, whereas males continued to feed for at least 26 d. Dispersal activity was initially high but decreased to low levels in 2–3 wk. After 6 wk, most adults were hiding inside tightly curled dry leaves and in the crevices of crumpled paper towel. Insects were held in a cold dark incubator (5°C) for at least 3 mo to terminate reproductive diapause. Females began ovipositing 4.4 d after being placed on yellow starthistle leaves at 19°C. The oviposition period lasted a mean of 20.6 d, and lifetime fecundity was 34.5 eggs. Daily fecundity was high during the first 14 d of oviposition (1.8 eggs/d) and declined to low levels (0.3 eggs/d). Feeding rate of ovipositing females during the first 2 wk was 19.2 holes/d, but this decreased to 4.7 holes/d for the remainder of the 45-d experiment. Female feeding rate was highly correlated to oviposition rate. Development time of eggs until eclosion of larvae at 19°C was 8.5 d and survivorship until eclosion was 73%. Development time from oviposition until adult emergence at ≈19°C was 77 d. These results provide a foundation for conducting experiments to evaluate host plant specificity and potential impact on the weed.

We quantified the density-dependent effects of herbivory by the psyllid Boreioglycaspis melaleucae Moore on the senescence of expanding and fully expanded leaves from two chemical variants (chemotypes) of the invasive tree Melaleuca quinquenervia (Cav.) S. T. Blake. Foliar chlorophyll content (OD) and percent nitrogen were not influenced by leaf age classes and chemotypes. In contrast, increases in the level of herbivory resulted in concomitant decreases in chlorophyll compared with undamaged leaves, with medium and high levels of herbivory reducing chlorophyll content by 64 and 72%, respectively. Likewise, low, medium, and high levels of herbivory resulted in 20, 53, and 60% reductions in percent nitrogen, respectively. Color analysis showed that increased herbivory also increased the amount of damaged tissue per leaf across both age classes, but younger leaves showed less susceptibility to herbivory than older leaves. Leaves sustaining moderate to high levels of herbivory progressed from dark green to yellow and finally to light tan as they deteriorated. These changes in color, particularly the yellowing aspect, were often more pronounced along the main leaf veins and vascular tissues. Feeding by B. melaleucae increased the likelihood of leaf abscission by 4.7-fold compared with leaves not subjected to herbivory and was not influenced by leaf age or chemotype. Implications for biological control of M. quinquenervia are discussed.

The leaf beetle Diorhabda elongata (Brullé) sensu lato has been released in the western United States for the classical biological control of exotic saltcedars (Tamarix species and hybrids). However, athel (T. aphylla [L.] Karsten), an exotic, moderately valued evergreen species in the southwestern United States and northern Mexico, has not been targeted for biological control. All populations of D. elongata previously examined, including those promising for release in southern areas of the saltcedar infestation, develop and oviposit on athel. Therefore, we assessed more fully the acceptability and suitability of athel to three D. elongata populations (Tunisia, Crete, and Uzbekistan). All populations of D. elongata laid similar numbers of eggs on athel and saltcedar in no-choice tests. In multiple- and paired-choice tests, oviposition on saltcedar was generally greater than on athel but with some notable exceptions and inconsistencies within populations. Increasing cage size delayed the colonization of and oviposition on test plants by small groups of adult beetles but did not change the pattern of egg-laying. For Crete beetles, survival and development were similar for larvae fed athel or saltcedar. Adult size was negatively affected by a larval diet of athel. An adult diet of athel did not reduce lifetime fecundity, although it did decrease egg mass size and delayed the start of oviposition. As a result, the innate capacity for increase decreased. The potential for damage to athel by D. elongata may be higher than previously thought; however, this may be offset by the potential for increased invasiveness of athel.

In some animals, transformation to the adult stage occurs in a hidden location, such as a burrow or a host. Males that can locate hidden females sooner, e.g., before they emerge, may have a mating advantage, particularly if the females are ready to mate. Whether males locate pre-emergent females and whether pre-emergent females will mate was examined in the parasitoid wasp Spalangia endius Walker. S. endius parasitize fly pupae. A single wasp offspring feeds, pupates, and transforms into an adult within the fly puparium (an outer shell around the fly pupa), and males emerge a day or more before females. Whether pre-emergent wasps are ready to mate was examined by dissecting them out of their hosts and presenting them with naturally emerged adults of the opposite sex. Many of the pre-emergent wasps were ready to mate. Nevertheless, males did not distinguish between hosts containing a pre-emergent female versus a pre-emergent male, or even between parasitized and unparasitized hosts. In contrast, males were able to differentiate between hosts from which a female versus a male had recently emerged. Although females are ready to mate before emergence, there may be little advantage to recognizing and staying with a host that contains a pre-emergent female because emergence takes so long, which raises the cost of missed mating opportunities elsewhere.

Pollen was found to significantly influence the host leaf selection and settling behaviors of certain thrips species (Thysanoptera: Thripidae). The effect of slash pine pollen (Pinus elliottii Engelm.) on the settling of Frankliniella occidentalis (Pergande) (western flower thrips) and Frankliniella fusca (Hinds) (tobacco thrips) was studied with leaf choice tests in peanut and tomato. In choice tests, F. occidentalis settling behavior was increased by seven-fold with the addition of pine pollen, but F. fusca was not significantly affected. In the flower thrips, the effect of pollen decreased over time without the renewal of pollen, suggesting thrips consumption of the pollen grains. These results support the idea that slash pine pollen has a greater impact on flower thrips (F. occidentalis) behavior than foliage thrips (F. fusca) behavior.

Maternal investment is strongly influenced by the availability of resources. A mother is expected to trade-off allocation to size, number, and sex of offspring to maximize her lifetime reproductive success. Optimal allocation is likely affected by ecological conditions that can alter the costs and benefits of different allocation decisions. When resources are rare, mothers have fewer resources to invest in offspring, likely altering optimal resource allocation. We examined maternal resource allocation to progeny under three different resource levels in semifield conditions for the solitary bee Megachile rotundata (Fabricius). We found that females with access to low resource levels invested less per individual daughter, but the same per individual son, and produced fewer total offspring compared with females with access to greater resource levels. Resource limitation had no impact on sex ratio.

Western flower thrips (Frankliniella occidentalis (Pergande), Thysanoptera: Thripidae) are a major pest of greenhouse ornamentals. Insecticides are the main control measure used for F. occidentalis on ornamentals and impede the use of biological control in the greenhouse. Flowering chrysanthemums, Dendranthema grandiflora (Tzvelev), could be used as trap plants (i.e., plants that are more attractive to a pest than the crop) in an integrated pest management (IPM) program for the control of F. occidentalis on potted chrysanthemum in greenhouses. This study focused on certain behavioral characteristics of F. occidentalis that can influence the efficiency of the trap plant strategy. First, host plant selection of adult F. occidentalis was studied by determining the influence of distance and stage of the crop on the attractiveness of flowering chrysanthemum as trap plants. Second, the influence of F. occidentalis colonization (resident versus dispersing F. occidentalis) on trap plant efficacy was determined. Flowering chrysanthemum plants were more attractive to adult F. occidentalis than the vegetative, bud, and crack-bud plant stages up to distances of 12 m, and trap plants were more effective at attracting dispersing F. occidentalis than resident F. occidentalis. It is concluded that flowering chrysanthemums have potential as trap plants for F. occidentalis in potted chrysanthemum before flowering.

Broadleaf weeds found in marginal areas by fields, roads, and ditches were controlled with herbicides in 23-km² areas of the Mississippi Delta in March or April of 1999, 2000, and 2001. There were two treated and two untreated 23-km² areas in each of the 3 test yr. The herbicides used were Trimec® or Strike 3™, and both contain mecoprop, 2, 4-D, and dicamba. Broadleaf weeds can serve as early season food and reproductive hosts for tarnished plant bugs, and population buildups can occur on these weeds before movement of plant bugs into cotton. Cotton fields in the treated sites and in untreated 23-km² sites were sampled for tarnished plant bugs weekly during June and July of all 3 yr. Overall mean numbers of tarnished plant bugs were significantly lower in cotton in the treated areas. The average reduction in overall mean numbers of plant bugs was 50% for the 3-yr period. Grower costs for insecticides used to control plant bugs were lower in cotton in the treated test sites in all 3 yr. The average net savings in plant bug control costs was estimated at $35,477/yr for growers in the treated areas over the 3 yr of the study. Elimination of broadleaf weeds was found to be an effective method for reducing numbers of plant bugs in cotton. However, it did not reduce numbers of tarnished plant bugs in any year to a level in cotton where additional control with insecticides was not needed.

Living mulches are cover crops grown concurrently within main crops for their benefits to weed control and soil quality. Because living mulches increase the diversity of vegetation in agricultural systems, they may impact the abundance or effectiveness of natural enemies. To examine the effects of living mulches on epigeal predators, arthropod abundance and feeding were examined in a rotation of corn (Zea mays L.), soybean (Glycine max L. Merr.), and forage crops in 2004 and 2005. Compared with a no-mulch control, the presence of alfalfa (Medicago sativa L.) and kura clover (Trifolium ambiguum M. Bieb.) mulches in corn and soybean increased predator abundance and consumption of European corn borer (Ostrinia nubilalis Hübner; Lepidoptera: Crambidae) pupae used as sentinel prey. A complementary effect of increased predation caused by corn and soybean was found when both annual crops with living mulches were compared with mulches grown alone. Positive correlations between the percentage of O. nubilalis pupae preyed on and ground beetle (Coleoptera: Carabidae) abundance suggest carabids contributed to the differences in predation. In 2005, fewer beetles correlated with consumption of O. nubilalis pupae [Poecilus chalcites (Say) and Scarites quadriceps Chaudior] were collected, and living mulch impacts on predation were less frequent. Both changes could be related to delayed herbicidal suppression of the living mulches in 2005, which seemed to homogenize predator community composition among the corn, soybean, and forage plots. Although living mulches alone may not provide sufficient pest suppression, their potential to enhance biological control should be considered along with their other agronomic benefits.

The effects of Bacillus thuringiensis (Bt) transgenic Ariete and Senia rice lines developed for the control of Chilo suppressalis Walker were evaluated on three nontarget stored product insect pests: the lepidopteran Plodia interpunctella (Hübner), the coleopteran Sitophilus oryzae L., and the psocid Liposcelis bostrichophila (Badonnel). Two different cry genes (cry1B and cry1Aa) under the control of a constitutive plant promoter (ubi) and a wound inducible promoter (mpi) were tested. Plodia interpunctella was unable to survive in rice semolina obtained from the two Ariete and Senia lines, which contained the ubi:cry1B gene. A reduction in S. oryzae adult progeny was observed in cultivar Senia rice containing the ubi:cry1B gene but not in cultivar Ariete rice. Moreover, a sublethal effect on S. oryzae adult progeny weight was observed in both of the rice cultivar treatments that constitutively expressed this gene. The number of L. bostrichophila emerging from Ariete rice containing the ubi:cry1B gene also was reduced. Both a reduction in the number of emerged adults and a delay in the development of P. interpunctella were observed for Ariete rice semolina containing the mpi:cry1B gene. However, no lethal or sublethal effects were observed for P. interpunctella reared on a transformed Senia rice line expressing the ubi:cry1Aa gene, suggesting possible tolerance to the toxin present in the rice grains. Although no increase in mortality was observed with S. oryzae fed ubi:cry1Aa rice, there was a sublethal effect on adult progeny weight.

Injuries caused by the western bean cutworm, Striacosta albicosta (Smith), on transgenic Cry1Ab Bacillus thuringiensis (Bt) corn hybrids were documented and quantified. The western bean cutworm is an emerging or potential pest of transgenic Bt corn in South Dakota. The proportion of ears infested with western bean cutworm larvae in the Cry1Ab Bt corn hybrids were 18–20, 38–70, and 0–34% in 2000, 2003, and 2004, respectively. The Cry1Ab Bt corn hybrids were almost completely free of European corn borer infestations. Untreated conventional corn hybrids were less infested with western bean cutworm larvae but more infested with European corn borer larvae. The proportion of ears infested with European corn borer larvae alone were 33, 58–80, and 8–25% in 2000, 2003, and 2004, respectively. Infestations with western bean cutworm alone were 28, 8–28, and 13–19%, respectively. Proportion of ears simultaneously infested with both western bean cutworm and European corn borer larvae were much lower than single infestations by either species alone, indicating niche overlap and competition. Simultaneous infestations by the two species on untreated conventional corn hybrids were only 8, 0–18, and 0–1% in 2000, 2003, and 2004. The corn grains harvested from injured ears were also analyzed for fumonisin and aflatoxin through quantitative enzyme-linked immunosorbent assays. More mycotoxins were found in 2003 when the levels of insect infestation in the corn ears were higher than in 2004. Results from this study underscore the need to investigate other emerging or potential arthropod pests of transgenic Bt corn hybrids in addition to the western bean cutworm.

The field efficacy of two transgenic rice lines, containing the Cry1Ac gene from Bacillus thuringiensis (Bt) and the CpTI (cowpea trypsin inhibitor) gene, on the striped stem borer, Chilo suppressalis (Walker), and population variation in susceptibility of C. suppressalis to the Bt insecticidal protein Cry1Ac were evaluated in Fuzhou, Fujian Province of China. The results of an open field test showed that the two transgenic lines exhibited high efficacy against natural infestations of C. suppressalis. In contrast, the untransformed parental control line showed serious damage symptoms not only in untreated plots, but also in plots treated with insecticides. The cumulative number of C. suppressalis adults derived from transgenic rice lines was significantly lower than that from control lines with and without chemical control treatments. Our results show that transgenic rice lines expressing Cry1Ac and CpTI have great potential for protecting rice from C. suppressalis damage with reduced use of insecticides. Comparison of pupal weight and fecundity of C. suppressalis between transgenic and control treatments indicated that pupal weight significantly decreased after continuously feeding on transgenic rice lines, but there was no significant effect on fecundity. Adult females of C. suppressalis were collected from light traps to ascertain population variation in susceptibility to Bt toxins. Each female producing enough fertile eggs for bioassays was used as the parent of an isofemale line. Of 1,100 females collected, 395 isofemale lines produced enough offspring to be screened on a diet assay treated with Cry1Ac. The results showed that 51.7% of isofemale lines were differentiated as highly susceptible, 23.0% as moderately susceptible, and 23.8% with low susceptibility; 1.5% were nonsusceptible, with a survival rate >70% and similar development as on the non-Bt control diet. The results indicated significant variation in susceptibility to Cry1Ac in the C. suppressalis population, which should be considered for insect resistance management of Bt rice in the future.