Late-Instar European Corn Borer (Lepidoptera: Crambidae) Tunneling and Survival in Transgenic Corn Hybrids

Field studies were conducted in 1996 and 1997 to determine injury by and survival of late-instar European corn borer, Ostrinia nubilalis (Hu¨ bner), on genetically altered Bacillus thuringiensis Berliner corn, Zea mays L. Cry1Ab events 176, Bt11, MON810, and MON802; Cry1Ac event DBT418; and Cry9C event CBH351 were evaluated. Plants of each corn hybrid were manually infested with two third-, fourth-, or Þfth-instar O. nubilalis. Larvae were held in proximity to the internode of the plant above the ear with a mesh sleeve. Larvae were put on the plants during corn developmental stages V8, V16, R1, R3, R4, R5, and R6. This study shows that not all B. thuringiensis hybrids provide the same protection against O. nubilalis injury. Hybrids with B. thuringiensis events Bt11, MON810, MON802, and CHB351 effectively protected the corn against tunneling by late-instar O. nubilalis. Event 176 was effective in controlling late-instar O. nubilalis during V12 and V16 corn developmental stages; however, signiÞcant tunneling occurred by fourth instars during R3 and R5. Event DBT418 was not effective in controlling late-instar O. nubilalis during corn vegetative or reproductive stages of development. Whether the B. thuringiensis hybrids satisÞed high- and ultrahigh- dose requirements is discussed

MANAGING EUROPEAN CORN BORER RESISTANCE TO BT CORN WITH DYNAMIC REFUGES

We develop a dynamic bioeconomic model of temporally optimal dynamic refuge recommendations for resistance management when a backstop technology arrives at a known date. The impact of the characteristics of the backstop on the use of the current technology, and the difference between static and dynamic refuges are examined.Crop Production/Industries,

MANAGING THE RISK OF EUROPEAN CORN BORER RESISTANCE TO TRANSGENIC CORN: AN ASSESSMENT OF CONTROVERSIAL REFUGE RECOMMENDATIONS

A bioeconomic model is developed to evaluate the tradeoff between the risk of resistance and increased productivity when refuge is planted in conjunction with transgenic pesticidal corn. The model is used to evaluate controversial refuge recommendations when producers are allowed to treat refuge in years of high pest pressure.Productivity Analysis, Research and Development/Tech Change/Emerging Technologies, Risk and Uncertainty,

BIOTECHNOLOGY AND PEST RESISTANCE: AN ECONOMIC ASSESSMENT OF REFUGES

Transgenic crops offer farmers a new and effective pest control option. However, the wide spread adoption of these crops could lead to a resistant pest population. This paper demonstrates how a pest refuge can be used to maximise the value of farm income in a dynamic model with genetic foundations.Crop Production/Industries, Research and Development/Tech Change/Emerging Technologies,

BT CORN AND INSECT RESISTANCE: AN ECONOMIC ASSESSMENT OF REFUGES

Genetically engineered crops offer farmers a new option for controlling pests. The high efficacy of these pesticidal crops, combined with the potential for widespread adoption, has raised concerns that pest resistance may prematurely diminish their value. In response to these concerns, the Environmental Protection Agency requires resistance management plans. Current resistance management plans rely on a high-dose refuge strategy. This analysis extends the current framework for evaluating high-dose refuge strategies to include a measure of agricultural productivity and conventional pesticide use. The economic tradeoff relative to agricultural productivity, conventional pesticide use, and pest resistance is assessed when Bt corn is planted to control the European corn borer.Crop Production/Industries,

Oviposition by European Corn Borer (Lepidoptera: Crambidae) in Response to Various Transgenic Corn Events

Oviposition preference by European corn borers, Ostrinia nubilalis (Hubner), for or against transgenic corn would influence amounts of refuge required for resistance management. The objective of this research was to determine if various Bacillus thuringiensis (Bt) corn transgenic events influence 0. nubilalis oviposition. All commercially available events (currently 5) were evaluated, plus 1 experimental event. Results from 3 independent studies are reported, including 3 field-cage experiments with vegetative corn, 2 field-cage experiments with reproductive corn, and 2 field experiments with natural 0. nubilalis on reproductive corn. In each case, Bt corn hybrids are compared with their near isogenic hybrids by counting numbers of egg masses on each plant type. More extensive comparisons were made in 3 of the experiments by determining the number, size, and location of egg masses on the corn hybrids. Moths laid more egg masses on Bt corn than on non-Bt corn in 1 cage experiment. These results, however, were not found in any of the other experiments. There is evidence that suggests cage effects influence moth oviposition more than Bt protein. Four of the 5 cage experiments and 2 field experiments indicate that the tested Bt events do not influence 0. nubilalis oviposition. Larval injury to isogenic corn during the vegetative stage did not influence adult oviposition during the corn reproductive stage when compared with Bt corn and noninjured isogenic corn. Based on these experiments, suggestions are made for future studies that use natural 0. nubilalis rather than 0. nubilalis in cages

Milkweed Matters: Monarch Butterfly (Lepidoptera: Nymphalidae) Survival and Development on Nine Midwestern Milkweed Species

The population of monarch butterflies east of the Rocky Mountains has experienced a significant decline over the past 20 yr. In order to increase monarch numbers in the breeding range, habitat restoration that includes planting milkweed plants is essential. Milkweeds in the genus Asclepias and Cynanchum are the only host plants for larval monarch butterflies in North America, but larval performance and survival across nine milkweeds native to the Midwest is not well documented. We examined development and survival of monarchs from first-instar larval stages to adulthood on nine milkweed species native to Iowa. The milkweeds included Asclepias exaltata (poke milkweed) (Gentianales: Apocynaceae), Asclepias hirtella (tall green milkweed) (Gentianales: Apocynaceae), Asclepias incarnata (swamp milkweed) (Gentianales: Apocynaceae), Asclepias speciosa (showy milkweed) (Gentianales: Apocynaceae), Asclepias sullivantii (prairie milkweed) (Gentianales: Apocynaceae), Asclepias syriaca (common milkweed) (Gentianales: Apocynaceae), Asclepias tuberosa (butterfly milkweed) (Gentianales: Apocynaceae), Asclepias verticillata (whorled milkweed) (Gentianales: Apocynaceae), and Cynanchum laeve (honey vine milkweed) (Gentianales: Apocynaceae). In greenhouse experiments, fewer larvae that fed on Asclepias hirtella and Asclepias sullivantii reached adulthood compared with larvae that fed on the other milkweed species. Monarch pupal width and adult dry mass differed among milkweeds, but larval duration (days), pupal duration (days), pupal mass, pupal length, and adult wet mass were not significantly different. Both the absolute and relative adult lipids were different among milkweed treatments; these differences are not fully explained by differences in adult dry mass. Monarch butterflies can survive on all nine milkweed species, but the expected survival probability varied from 30 to 75% among the nine milkweed species

Fusarium Ear Rot and Fumonisins in Bt and Conventional Corn Hybrids, 1998

Fusarium ear rot and fumonisin concentrations were compared within five pairs of Bt and near-isogenic conventional hybrids in a replicated field plot at the Iowa State University Johnson Research Farm in Story Co., IA. For each of the five commercially available Bt transformation events, a representative commercial hybrid and its near-isogenic conventional counterpart were included. The 17-ft, four-row plots were planted on 13 May with 30 in row spacing and 120 seeds per plot. The experimental design was a randomized complete block with eight replications. The previous crop was soybeans