Robert N. Wiedenmann

Tritrophic Interactions Among Bt (Cry3Bb1) Corn, Aphid Prey, and the Predator Coleomegilla maculata (Coleoptera: Coccinellidae)

Abstract The ability of the transgenic corn rootworm resistant corn (Zea mays L.) hybrid, MON 863, to affect the predator Coleomegilla maculata DeGeer (Coleoptera: Coccinellidae) through the consumption of corn-fed aphid (Rhopalosiphum maidis, Homoptera: Aphididae) prey was examined in the laboratory. Aphid weight was used as an index of prey quality. Larvae of C. maculata were reared to pupation on aphids that had consumed transgenic or nontransgenic (susceptible) corn plants. Larval duration, survivorship to pupation, postmortem adult dry weight (taken at 30 d after eclosion), adult mobility, and fecundity were compared for C. maculata between treatments. Fitness parameters of C. maculata were similar between transgenic and susceptible treatments, despite a 33% reduction in the weight of aphid prey reared on MON 863. Using immunostrip tests, Cry3Bb1 was detectable in the leaves of MON 863 but not in the susceptible plant, aphids, or C. maculata that were fed aphids. We conclude that transgenic corn that expresses Cry3Bb1 does not inflict acute or chronic degradations in fitness on individual C. maculata through aphid prey, but these results do not necessarily apply to other natural enemies, herbivores, or insect-resistant corn hybrids.

Assessing Nontarget Impacts of Bt Corn Resistant to Corn Rootworms: Tier-1 Testing with Larvae of Poecilus chalcites (Coleoptera: Carabidae)

Abstract A dietary exposure bioassay with larvae of the ground beetle, Poecilus chalcites (Say) (Coleoptera: Carabidae), was developed to assess potential nontarget impacts of corn event MON 863 expressing the Cry3Bb1 protein for control of corn rootworms, Diabrotica spp. (Coleoptera: Chrysomelidae). The assay involved 28 d of continuous exposure of P. chalcites larvae to an artificial diet treated with a maximum hazard dose (930 μg/g of diet) of the Cry3Bb1 protein. Results from this study showed that the Cry3Bb1 protein at a concentration of 930 μg/g of diet had no adverse effect on the survival, development, and growth (biomass) of P. chalcites larvae. Furthermore, statistical power analysis indicated that at levels of 80% power and 5% type I error rate, the study design would have been able to detect a minimum 14 (at day 7) to 19% (at days 14, 21, and 28) reduction in survival and a 21 (at day 14) to 18% (at day 28) reduction in biomass of test larvae relative to the negative buffer control groups. Based on the maximum level (93 μg/g) of the Cry3Bb1 protein expressed in MON 863 corn tissues including leaves, roots, and pollen, findings from this study indicate that corn hybrids containing the MON 863 event have a minimum 10 times safety factor for larvae of P. chalcites, and thus pose little risk to this nontarget beneficial insect.

Symposium: Insect Behavioral Ecology--'86: Adaptations of Arthropod Predators to Agricultural Systems

Agricultural systems are habitat islands that are colonized by generalist arthropod predators. How predators find prey and apportion captured prey energy into competing physiologic demands are central adaptations that provide for the subsistence of predator populations. We have found that predators in soybeans maintain a low, consistent rate of predation, and compensate for changes in leaf area, the searching universe of predators in soybeans. Predators maintain survivorship but not reproductive effort at low prey inputs suggesting physiologic trade-offs at low prey densities. We find a major discrepancy between functional response theory and our field results, and suggest an alternative framework for study of predation under field-realistic conditions.

Dimethylfuran-lactone pheromone from males of Galerucella calmariensis and Galerucella pusilla.

Male Galerucella calmariensis and Galerucella pusilla (Coleoptera: Chrysomelidae) emit an aggregation pheromone while feeding on host foliage. Isolation of the compound from collected volatiles was guided by comparisons of gas chromatograms of extracts from males and females and by gas chromatography–electroantennographic detection. The compound was identified by a combination of spectrometric methods and microchemical tests as the novel dimethylfuran lactone, 12,13-dimethyl-5,14-dioxabicyclo[9.2.1]tetradeca-1(13),11-dien-4-one. The structure was confirmed by synthesis, and the synthetic compound attracted males and females of both species in field bioassays. These beetles were previously introduced into North America as biological control agents for the invasive wetland weed, purple loosestrife Lythrum salicaria, and the pheromone could become a tool for monitoring populations. A new method is described for distinguishing the two species based on the tibial spurs of the males.

Rearing Protocol and Life History Traits for Poecilus chalcites (Coleoptera: Carabidae) in the Laboratory

A rearing protocol for the predaceous ground beetle, Poecilus chalcites (Say), is described. The effects of dietary constituents, substrate moisture content, and substrate type on larval developmental rates and size were examined in the laboratory. The protocol was successful in obtaining nearly 80% pupation rates, although adult size was smaller than fieldcollected beetles, and laboratory-produced adults did not lay eggs. We determined experimentally that some of the components of the meridic diet used for colony production could be removed without compromising larval size or developmental rates, but that nutrition beyond cat food was necessary to increase larval size. We found a positive correlation of larval size with increased moisture content using vermiculite substrate at three moisture levels (33.3, 50.0 and 66.7% by weight). Untreated Fer-TiI (GreenGro Products, Jackson, WI) soil resulted in the highest pupation rate (70 to 80%) and had one of the shortest developmental periods of the five soils tested. Steaming or sifting Fer-Til soil compromised its ability to support larval development until pupation.

Avoiding conflicts between insect and weed biological control: selection of non-target species to assess host specificity of cabbage seedpod weevil parasitoids

Abstract:  Classical biological control of insect pests and weeds may lead to potential conflicts, where insect pests are closely related to weed biological control agents. Such a conflict may occur in the classical biological control of the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) in North America, which belongs to the same subfamily, Ceutorhynchinae, as a number of agents introduced or proposed for introduction against non‐indigenous invasive weed species. We propose a step‐by‐step procedure to select non‐target species and thereby to develop a non‐target species test list for screening candidate entomophagous biological control agents of a herbivore pest insect in a way that would simultaneously evaluate non‐target potential on weed biological control agents and other non‐target species. Using these recommendations, we developed a non‐target test list for host specificity evaluations in the area of origin (Europe) and the area of introduction (North America) for cabbage seedpod weevil parasitoids. Scientifically based predictions on expected host–parasitoid interactions and ecological information about the ecological host range in the area of origin can help avoid conflicts, while still allowing the introduction of safe and effective agents against both insect pests and weeds.

Ovipositional Preferences of the Japanese Beetle (Coleoptera: Scarabaeidae) Among Warm- and Cool-Season Turfgrass Species

ABSTRACT Japanese beetles, Popillia japonica Newman (Coleoptera: Scarabaeidae), were evaluated for ovipositional preferences among four turfgrasses common in northwestern Arkansas. Choice assays revealed females preferred to oviposit in tall fescue (Festuca arundinacea Schreb.) and zoysiagrass (Zoysia japonica Steud.), and that they avoided oviposition in common bermudagrass (Cynodon dactylon [L.] Pers.) and hybrid bermudagrass (C. dactylon x C. transvaalensis Pers.). Significantly fewer eggs were oviposited in hybrid bermudagrass in a no-choice assay, suggesting that chemical and/or physical plant characteristics deter oviposition in that grass. The percentage of turfgrass cores with evidence of female activity (presence of female or eggs, or signs of female digging) in choice assays revealed no differences among treatments, yet significantly fewer hybrid bermudagrass cores had eggs. These results suggest that many females did not initially reject hybrid bermudagrass based on aboveground plant characteristics, but rather they left without ovipositing. Therefore, resistance in hybrid bermudagrass is likely expressed below ground. Our results suggest that the use of hybrid bermudagrass as a means of cultural control in an integrated pest management program may discourage Japanese beetle oviposition and subsequent grub infestations in lawns, golf courses, or sports fields.

Ground Beetle (Coleoptera: Carabidae) Assemblages in Mulched and Non-Mulched Garden Plots

Abstract Ground beetles (Coleoptera: Carabidae) are important generalist predators in a variety of habitats, where they prey on many kinds of pest insects. We used pitfall traps for weekly collections by Master Gardener volunteer researchers for 13 weeks in 1998 and 12 weeks in 1999 to assess species composition and temporal patterns of ground beetles in plots of potatoes in home gardens in Illinois and Indiana. Potato plots were either mulched with straw or were left unmulched, having bare soil between plant rows. A total of 82 individuals of 9 species was found in 1998 in mulched plots, versus 79 individuals of 10 species found in unmulched plots. In 1999, 639 individuals of 23 species were collected in mulched plots, versus 380 individuals of 31 species in unmulched plots. Significantly more Cyclotrachelus sodalis (LeConte) were found in mulched plots than in unmulched plots in 1999, whereas there were no significant differences between mulched and unmulched plots in numbers of Cyclotrachelus convivus (LeConte), Harpalus pensylvanicus DeGeer, Pterostichus permundus (Say) or Scarites subterraneus F. Species diversity, as measured by the Shannon Diversity Index, was significantly greater in unmulched plots than in mulched plots in 1999. Fourteen species collected in unmulched plots in 1999 were not found in mulched plots, whereas 6 species found in mulched plots were not found in unmulched plots. Although ground beetle assemblages differed as a function of habitat manipulation, exact diets of carabids need to be understood to know the potential to impact pest management in home gardens.

Larinus minutus (Coleoptera: Curculionidae), A Biological Control Agent of Spotted Knapweed (Centaurea stoebe ssp. Micranthos), Established in Northern Arkansas

Larinus minutus Gyllenhal (Coleoptera: Cur culionidae) is a univoltine weevil that feeds on the seeds of spotted and diffuse knapweeds Centau rea stoebe ssp. micranthos (Gugler) Hayek and C. diffusa Lamarck. After emerging from overwin tering sites in the leaf litter, adult weevils begin feeding on the vegetative portions of the plants. Adults, however, prefer to feed on flowers when they are available and development of beetle ova ries is dependent upon flower feeding (Groppe 1990). Females oviposit on newly opened flower heads (capitula). Two or 3 eggs can occur in each flower head, but only 1 larva usually develops in smaller capitula. Multiple larvae can survive in large spotted knapweed capitula (Groppe 1990). Under laboratory conditions (25°C), eggs hatch in 3-4 d (Groppe 1990). Larval development takes approximately 4 weeks and larvae go through 3 instars. Larvae feed on knapweed seeds and pu pate in the capitula, making a cocoon out of the seed head material (Kashefi & Sobhian 1998). Larvae can destroy up to 100% of the seeds in a capitulum (Kashefi & Sobhian 1998). In the West ern United States, adult weevils emerge in late Sep and feed on plants until winter, when the adults overwinter in leaf litter and emerge in the following Jun (Jordan 1995). Larinus minutus was first released into the United States in 1991 with collections from Greece and Romania (Story 2002). Although 12 other natural enemy species were introduced into the Western United States and Canada to control spotted and diffuse knapweeds, only recently has adequate suppression of some populations been seen (Myers 2004; Smith 2004). Myers (2007) sug gested that knapweed populations did not signif icantly decline until the establishment of L. minutus. Populations of L. minutus have been es tablished in Washington, Wyoming, Oregon, Mon tana, Minnesota, Colorado, and Indiana (Lang et al. 1996; Story 2002). No natural enemies of spotted knapweed have been released in Arkansas until the inception of this study. However, we found Urophora quadrifasciata (Meigen) (Diptera: Tephritidae) established throughout the range of spotted knapweed in the state in a survey in 2006 for knapweed natural ene mies. This seedhead galling fly was introduced from Russia into Canada in 1980 and has since been re distributed or spread on its own to several states in the northeastern and northwestern United States (Story 2002). Duguma (2008) found that U. quadri fasciata reduced the number of seeds produced by spotted knapweed by 44% late in the season (Aug), at a time when plants are more environmentally stressed. However, the fly did not significantly re duce the number of seeds produced earlier in the season, a time when knapweed is most robust (Du guma 2008). Thus, it is likely that U. quadrifasciata alone will not significantly suppress knapweed pop ulations in Arkansas, or stop its spread further into the southern United States.

Seasonal Dynamics of Urophora Quadrifasciata on Spotted Knapweed in the Arkansas Ozarks

Abstract Periodic sweep-net sampling and capitula sampling were conducted between April and October 2007 to determine the seasonal phenology of Urophora quadrifasciata (Meigen) (Diptera: Tephritidae) on spotted knapweed, Centaurea stoebe subsp. micranthos (Gugler) Hayek (Asteraceae), in the Arkansas Ozarks of the United States of America. Urophora quadrifasciata produces up to three generations in Arkansas, rather than being bivoltine as in the northern United States of America. The first, second, and third generations of U. quadrifasciata reached peak adult numbers around 26 May, 29 June, and 27 July, respectively. Males tended to emerge earlier than females but the female:male ratio was approximately 1:1 for most of the season. The majority of the offspring of the three generations emerged between June and October, while approximately 38% entered diapause and emerged as adults in April–June of the following year; 3.4 ± 0.1 (mean ± SE) (range 1–12) flies emerged from each infested capitulum. The absence of other, competing knapweed biological control agents as well as very low rates of parasitism, mild weather conditions, and a longer knapweed growing season likely contributed to the adaptation and establishment of U. quadrifasciata on spotted knapweed in Arkansas.