Survival, Development, and Oviposition of Resistant Diamondback Moth (Lepidoptera: Plutellidae) on Transgenic Canola Producing a Bacillus thuringiensis Toxin

We measured responses of diamondback moth, Plutella xylostella L., to transgenic and nontransgenic canola, Brassica napus L. Transgenic canola expressed a cry1Ac gene of Bacillus thuringiensis Berliner resulting in 238 ±29 ng of Cry1Ac protein per milligram of total extractable protein in leaves. We tested 2 Hawaiian strains of diamondback moth: NO-QA was resistant to Cry1Ac and LAB-PS was susceptible. Larval and pupal durations, pupal weights, and adult emergence of the 2 strains were similar on nontransgenic canola, but differed significantly on transgenic canola. Transgenic canola killed all larvae tested from the susceptible strain. In contrast, for the resistant strain, no differences occurred between transgenic and nontransgenic canola in larval survival and head capsule width at day 5, percentage pupation, pupal weight, percentage adult emergence, and extent of defoliation. For both the susceptible and resistant strains of diamondback moth, no differences were detected between transgenic and nontransgenic canola in feeding initiation or oviposition preference. The lack of discrimination between transgenic and nontransgenic canola by neonates and ovipositing females indicates that host choice behavior is independent from susceptibility to Cry1Ac. Development of resistant diamondback moth on transgenic canola without any adverse effects provides an example of a pest that has completely overcome high levels of a B. thuringiensis toxin expressed by a genetically engineered plant.