Agricultural crops that express the Bacillus thuringiensis (Bt) toxin are extremely effective at killing targeted pests, resulting in strong selective pressure to increase the frequency of resistant genotypes. Repeated use of such crops over time and space can increase the rate of resistance evolution in pest populations. Factors other than selection intensity can influence this rate, but the relative importance of these factors is not clear. Natural enemies have the potential to increase or decrease the rate of resistance evolution in a pest population by differentially impacting susceptible and resistant individuals. In the Bt-corn system, the European corn borer (ECB), Ostrinia nubilalis, is attacked by a specialist parasitoid, Macrocentrus grandii. It is hypothesized that limited dispersal or a strong direct density dependent response by M. grandii could create a spatial refuge for resistant ECB larvae that survive in a Bt field, favoring an increase in the frequency of the resistant genotype, while a high dispersal ability and a strong inverse density dependent response may increase the probability that M. grandii locate resistant ECB larvae. We estimated the parasitoidís dispersal range and tested for spatial density dependence by collecting ECB larvae at 200 sample sites in a grid pattern within 8 ha non-Bt corn fields. The probability of being parasitized in Bt and non-Bt fields was compared by outplanting ECB larvae in paired Bt/non-Bt fields and calculating percent parsitism.
Species 1: Lepidoptera Crambidae Ostrinia nubilalis (European corn borer)
Species 2: Hymenoptera Braconidae Macrocentrus grandii
Species 3: Bacillales Bacillaceae Bacillus thuringiensis
Keywords: density dependence, insecticide resistance
Back to Student Competition Ten-Minute Papers, Ca1, Biological Control
Back to Student Competition TMP Orals
Back to The 2003 ESA Annual Meeting and Exhibition