Field performance of western corn rootworm (Diabrotica virgifera virgifera) colonies selected on transgenic corn in the greenhouse

To delay evolution of insect resistance to transgenic crops producing Bacillus thuringiensis (Bt) toxins, nearby "refuges" of host plants not producing Bt toxins are required. Such refuges are expected to be most effective in slowing resistance when the toxin concentration in Bt crops is high enough to kill all or nearly all insects heterozygous for resistance. However, Bt corn, Zea mays, introduced recently does not meet this "high-dose" criterion for control of western corn rootworm (WCR), Diabrotica virgifera virgifera. Rootworm adults were collected from three locations within the north central United States and used to initiate laboratory colonies. Progeny from each location were then either reared on Cry3Bb1-expressing corn (selected) or its isoline (control) in the greenhouse. Following rearing in the greenhouse for up to seven generations, selected and control colonies from each location were screened in the field on Cry3Bb1-expressing corn or it’s isoline. After correcting for differences in hatch, ~twice as many larvae of selected colonies were recovered from Bt compared to control colonies. Larvae of control colonies did little damage to Bt corn roots but removed more than half a node of roots from isoline plants. Within the selected colonies, damage to Bt and isoline plants was not significantly different. Rapid response to selection in the absence of mating to susceptible beetles has been documented in all populations evaluated to date.