K. R. Ostlie

Biological Control of the Western Corn Rootworm (Coleoptera: Chrysomelidae) Using the Entomopathogenic Nematode, Steinernema carpocapsae

Abstract A series of field trials evaluated the efficacy of the entomopathogenic nematode, Steinernema carpocapsae Weiser All strain for control of western corn rootworm, Diabrotica virgifera virgifera LeConte, larvae. Separate trials examined the effects of nematode application rate and timing on corn rootworm control in 1991. In the rate trial, S. carpocapsae (0, 104, 105, 106, and 107 nematodes per 30.5 row-cm) was applied as the insect population entered the second instar. Nematode treatment significantly reduced corn root injury and adult emergence. High application rates (106 and 107 nematodes per 30.5 row-cm) significantly outperformed low rates (104 and 105 nematodes per 30.5 row-cm). Nematode treatment (500,000 S. carpocapsae per 30.5 row-cm) reduced root injury and adult emergence slightly in the timing trial; later applications (second, third instar) were numerically, but not significantly, more effective than early (egg, first instar) ones. In 1992, a factorial trial combined four application dates (egg; first, second, third instar) and five rates (0, 104, 105, 106, 107 S. carpocapsae per 30.5 row-cm). Later applications (second, and particularly, third instar) were significantly more effective than early (egg, first instar) ones. Root injury and adult emergence in control and low rate (104 and 105 nematodes per 30.5 row-cm) plots significantly exceeded that in high rate (106 and 107 nematodes per 30.5 row-cm) plots. Commercially acceptable root protection (root injury ratings below 3.0) was provided by 106 nematodes per 30.5 cm of row applied to third instars, and by 107 nematodes per 30.5 cm of row applied to second and third instars.

Crafting crop resistance to corn rootworms

Transgenic corn co-expressing two complementary endotoxins from Bacillus thuringiensis shows promise in controlling these pernicious pests, but questions remain on how best to avoid the emergence of resistance.

Minnesota field population of western corn rootworm (Coleoptera: Chrysomelidae) shows incomplete resistance to Cry34Ab1/Cry35Ab1 and Cry3Bb1

In the United States of America, the western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), is commonly managed with transgenic corn (Zea mays L.) expressing insecticidal proteins from the bacteria Bacillus thuringiensis Berliner (Bt). Colonies of this pest have been selected in the laboratory on each commercially available transformation event and several resistant field populations have also been identified; some field populations are also resistant. In this study, progeny of a western corn rootworm population collected from a Minnesota corn field planted to SmartStax® corn were evaluated for resistance to corn hybrids expressing Cry3Bb1 (event MON88017) or Cry34/35Ab1 (event DAS‐59122‐7) and to the individual constituent proteins in diet‐overlay bioassays. Results from these assays suggest that this population is resistant to Cry3Bb1 and is incompletely resistant to Cry34/35Ab1. In diet toxicity assays, larvae of the Minnesota (MN) population had resistance ratios of 4.71 and >13.22 for Cry34/35Ab1 and Cry3Bb1 proteins, respectively, compared with the control colonies. In all on‐plant assays, the relative survival of the MN population on the DAS‐59122‐7 and MON88017 hybrids was significantly greater than the control colonies. Larvae of the MN population had inhibited development when reared on DAS‐59122‐7 compared with larvae reared on the non‐Bt hybrid, indicating resistance was incomplete. Overall, these results document resistance to Cry3Bb1 and an incomplete resistance to Cry34/35Ab1 in a population of WCR from a SmartStax® performance problem field.

Conducting public-sector research on commercialized transgenic seed: In search of a paradigm that works

Public-sector scientists have a mandate to independently evaluate agricultural products available to American farmers on the open market, whereas the companies that sell the products must protect their intellectual property. However, as a consequence of the latter concern, public scientists currently are prohibited by industry-imposed restrictions from conducting research on commercialized transgenic seed without permission of the company. Industry acknowledged the seriousness of the problem after public warnings by a large group of entomologists to EPA and scientific advisory panels that the assumption of independence of public-sector studies on these products is no longer valid under current restrictions. Both industry and public scientists are working to find an amicable, mutually-acceptable solution. Recently, the American Seed Trade Association brokered a draft set of principles designed to protect the legitimate property rights of companies while allowing public scientists independence to conduct most types of research on their commercialized products without the need for case-by-case agreements. While there are a number of potential pitfalls in implementation of the principles across companies, this effort represents a major step forward, and there is reason for optimism that this approach can be made to work to the benefit of industry, public scientists, and the American public.

Farmer Demand For Corn Rootworm Bt Corn: Do Insect Resistance Management Guidelines Matter?

Farmer adoption of Bt corn and compliance with insect resistance management (IRM) regulations will influence the success of these regulations. The purpose of this paper is to use farmer survey data to estimate the demand for new corn rootworm Bt corn and the cost of complying with proposed IRM regulations.

Nitrogen Rate Effects on Cry3Bb1 and Cry3Bb1 + Cry34/35Ab1 Expression in Transgenic Corn Roots, Resulting Root Injury, and Corn Rootworm Beetle Emergence

Nitrogen (N) application rates have been recommended historically for maximum economic yield of corn (Zea mays L.), but not for optimal expression or impacts of Bt (Bacillus thuringiensis Berliner) Cry protein(s) on target insects. This study explored the need to adjust N rates to optimize expression of corn rootworm-active Bt (Bt-RW) protein(s) in a single and a pyramided trait hybrid and resulting impacts on beetle emergence and root injury, under field conditions. The experiment featured a factorial treatment arrangement in a split-plot randomized complete block design with six N rates as the main plots and three hybrids (MON88017 expressing Cry3Bb1, MON88017 x DAS-59122 expressing Cry3Bb1 + Cry34/35Ab1, and a non-Bt-RW hybrid) as the subplots. Corn roots were sampled at the beginning of, and after, peak larval feeding to determine Bt-expression levels using an enzyme-linked immunosorbent assay. Beetles were collected every 2-3 d during emergence using cut-plant emergence cages. Cry3Bb1 expression was significantly reduced when little or no N was applied. Cry34Ab1 and Cry35Ab1 expression was highly variable and unaffected by N rate. Beetle emergence increased with N rate in the non-Bt-RW hybrid while root injury declined. Provided Bt-RW hybrids had sufficient applied N, root injury was relatively low. Results indicate that N management could affect Bt-RW expression and success of insect resistance management plans provided N is applied at rates that enhance production of susceptible beetles emerging from the non-Bt-RW (refuge) hybrid, and achieve optimal expression and efficacy of Bt traits.