The corn rootworm complex (Coleoptera: Chrysomelidae) constitutes a significant threat to maize production in the United States, and more recently, in Europe. We conducted an analysis of readily available field trial data to validate an existing damage function for corn rootworm larvae. We used a nested error component model with unbalanced panel data to describe the relationship between yield loss and root injury caused by these insects. These data were collected by personnel with the Insect Management and Insecticide Evaluation Programme (Department of Crop Sciences, University of Illinois) and represent 19 location‐years. To our knowledge, this is the largest data set used to estimate a damage function for corn rootworm larvae. Unlike many experiments examining the relationship between root injury and yield loss caused by corn rootworm larvae, the data set used for our analysis includes many Bt maize hybrids. Our model suggests that for each node of roots injured by corn rootworm larvae, a yield loss of approximately 15% can be expected. Statistically significant variance components included an effect of location and experimental error. We speculate that variation in weather across experimental sites was the principal factor contributing to the significant effect of location. The substantial experimental error observed for our model highlights the limitations of utilizing a multi‐year, geographically diverse damage function for predicting yield loss because of root injury on a small scale. We discuss major factors contributing to the variance components estimated by our model and suggest techniques for improving future analyses of the damage function for corn rootworm larvae.

A 2-yr field experiment was conducted to determine the effects on Diabrotica spp. (Coleoptera: Chrysomelidae) of an insecticidal seed treatment (Poncho 1250, (AI) /clothianidin) and a granular insecticide (Aztec 2.1G, (AI)/tebupirimphos and cyfluthrin) alone and in combination with maize producing the insectidical toxin Cry3Bb1 derived from the bacterium Bacillus thuringiensis (Bt). Yields for Bt maize plots were significantly greater than for non-Bt maize; however, insecticides did not significantly affect yield. Insecticides significantly decreased root injury in non-Bt maize plots, but there were no significant differences in root injury between Bt maize with or without either insecticide. Maize producing the Bt toxin Cry3Bb1 and the soil-applied insecticide Aztec significantly decreased survival of western corn rootworm (Diabrotica virgifera virgifera LeConte), while only Bt maize significantly decreased survival of the northern corn rootworm (Diabrotica barberi Smith & Lawrence). For both species, Bt maize and each of the insecticides delayed emergence. In the absence of density-dependent mortality, Bt maize imposed 71 and 80% reduction in survival on the western corn rootworm and the northern corn rootworm, respectively. The data from this study do not support combining insecticide with Bt maize because the addition of insecticide did not increase yield or reduce root injury for Bt maize, and the level of rootworm mortality achieved with conventional insecticide was likely too low to delay the evolution of Bt resistance. In addition, delays in emergence from Bt maize combined with insecticides could promote assortative mating among Bt-selected individuals, which may hasten resistance evolution. RightsThis article is the copyright property of the Entomological Society of America and may not be used for any commercial or other private purpose without specific permission of the Entomological Society of America.This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/ent_pubs/175BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. ABSTRACT A 2-yr Þeld experiment was conducted to determine the effects on Diabrotica spp. Effect of Bt(Coleoptera: Chrysomelidae) of an insecticidal seed treatment (Poncho 1250, (AI)/clothianidin) and a granular insecticide (Aztec 2.1G, (AI)/tebupirimphos and cyßuthrin) alone and in combination with maize producing the insectidical toxin Cry3Bb1 derived from the bacterium Bacillus thuringiensis (Bt). Yields for Bt maize plots were signiÞcantly greater than for non-Bt maize; however, insecticides did not signiÞcantly affect yield. Insecticides signiÞcantly decreased root injury in non-Bt maize plots, but there were no signiÞcant differences in root injury between Bt maize with or without either insecticide. Maize producing the Bt toxin Cr...

The transgenic maize (Zea mays L.) event MON 88017 produces the Bacillus thuringiensis Berliner (Bt) toxin Cry3Bb1 to provide protection from western corn rootworm (Diabrotica virgifera virgifera LeConte) larval feeding. In response to reports of reduced performance of Cry3Bb1-expressing maize at two locations in Illinois, we conducted a two-year experiment at these sites to characterize suspected resistance, as well as to evaluate root injury and adult emergence. Single-plant bioassays were performed on larvae from each population that was suspected to be resistant. Results indicate that these populations had reduced mortality on Cry3Bb1-expressing maize relative to susceptible control populations. No evidence of cross-resistance between Cry3Bb1 and Cry34/35Ab1 was documented for the Cry3Bb1-resistant populations. Field studies were conducted that included treatments with commercially available rootworm Bt hybrids and their corresponding non-Bt near-isolines. When compared with their near-isolines, larval root injury and adult emergence were typically reduced for hybrids expressing Cry34/35Ab1 either alone or in a pyramid. In many instances, larval root injury and adult emergence were not significantly different for hybrids expressing mCry3A or Cry3Bb1 alone when compared with their non-Bt near-isolines. These findings suggest that Cry34/35Ab1-expressing Bt maize may represent a valuable option for maize growers where Cry3Bb1 resistance is either confirmed or suspected. Consistent trends in adult size (head capsule width and dry mass) for individuals recovered from emergence cages were not detected during either year of this experiment. Because of the global importance of transgenic crops for managing insect pests, these results suggest that improved decision-making for insect resistance management is needed to ensure the durability of Bt maize.

Soybean aphid (Aphis glycines Matsumura) is a native pest of soybean [Glycine max (L.) Merr.] in eastern Asia and was detected on soybeans in North America in 2000. In 2004, the soybean cultivar Dowling was described to be resistant to soybean aphids with the Rag1 gene for resistance. In 2006, a virulent biotype of soybean aphid in Ohio was reported to proliferate on soybeans with the Rag1 gene. The objective was to survey the occurrence of virulent aphid populations on soybean indicator lines across geographies and years. Nine soybean lines were identified on the basis of their degree of aphid resistance and their importance in breeding programs. Naturally occurring soybean aphid populations were collected in 10 states (Kansas, Illinois, Indiana, Iowa, Michigan, Minnesota, North Dakota, Ohio, South Dakota, and Wisconsin) and the Canadian province of Ontario. The reproductive capacity of field‐collected soybean aphid populations was tested on soybean lines; growth rates were compared in no‐choice field cages at each geographic region across 3 yr. The occurrence of soybean aphid biotypes was highly variable from year to year and across environments. The frequency of Biotypes 2, 3, and 4 was 54, 18, and 7%, respectively, from the 28 soybean aphid populations collected across 3 yr and 11 environments. Plant introduction (PI) 567598B, a natural gene pyramid of rag1c and rag4, had lowest frequency of soybean aphid colonization (18%). Several factors may have contributed to the variability, including genetic diversity of soybean aphids, parthenogenicity, abundance of the overwintering host buckthorn (Rhamnus spp.), and migratory patterns of soybean aphids across the landscape.