Estimating western corn rootworm (Coleoptera: Chrysomelidae) larval susceptibility to event DAS‐59122‐7 maize

Susceptibility of Diabrotica virgifera virgifera (LeConte) larvae to DAS‐59122‐7 maize was evaluated using a laboratory technique that measures rootworm survival to adulthood on maize seedlings. This method produces direct measures of larval susceptibility using realistic exposure to the same range of insecticidal protein concentrations found in field‐grown DAS‐59122‐7 maize roots. First, second and third instars were reared to adulthood on DAS‐59122‐7 maize seedlings or a non‐transgenic, near‐isoline maize. Data on survival, adult gender ratio, adult weight and median emergence were collected. Overall, larval susceptibility to DAS‐59122‐7 maize was lower than earlier predictions ( Storer et al. 2006 ). Neonate survival on DAS‐59122‐7 maize was approximately 33% of isoline survival after 17 days, and the same 33% recovered and developed to adulthood when the isoline maize was substituted. Survival rate on DAS‐59122‐7 maize increased with instar. The mean survivorship was 0.5%, 26% and 65% when exposure to DAS‐59122‐7 maize began at the first, second and third instars, respectively. Exposure to DAS‐59122‐7 maize led to sub‐lethal effects on adult gender ratio, weight and median emergence. These effects decreased when exposure to DAS‐59122‐7 maize began at later instars. The killing effect of DAS‐59122‐7 maize on rootworm larvae appeared to result from the combined chronic effects and absence of a suitable host as perceived by the larvae. The relevance of these data and the methodology of estimating rootworm susceptibility to plant‐incorporated protectants are discussed in the context of the US Environmental Protection Agency’s functional definition of ‘high dose’ and use of refuge for resistance management ( EPA 1998a ). Based on these results it is evident that DAS‐59122‐7 maize does not meet the functional definitions of high dose as described by EPA (1998a,b) and ILSI (1999) , and the utility of refuge, refuge size and refuge placement for delaying rootworm resistance should be further investigated.