Suppression of diamondback moth using Bt-transgenic plants as a trap crop

Several types of trap crops have been recommended for managing the diamondback moth, Plutella xylostella, including collards (Brassica oleracea var. acephala) and Indian mustard (Brassica juncea L.). However, results have been variable perhaps because populations of P. xylostella develop on these trap crops and spill over to the cash crop. To overcome this problem, we sought to develop “dead-end” trap crops that were more attractive for oviposition than the cash crop but on which P. xylostella larvae cannot survive. We have produced Bacillus thuringiensis (Bt)-transgenic collard and Indian mustard lines with a cry1C gene that have the potential to be used as a “dead-end” trap crop for P. xylostella. Greenhouse and small cage studies confirmed the control of P. xylostella larvae on the Bt crops. Furthermore, Indian mustard was significantly preferred over cabbage and collards for oviposition, regardless of whether the Indian mustard was Bt or non-Bt. The use of Bt Indian mustard as a trap crop significantly reduced the number of larvae that appeared on a cabbage cash crop, compared with using a non-Bt Indian mustard trap crop. However, this reduction also occurred when using Bt collards as a trap crop, despite collards being less preferred for oviposition. In fact, despite the overall increase in oviposition caused by the presence of Indian mustard compared with collards, the use of either Bt Indian mustard or Bt collards provided the same level of protection to the cash crop. Both plants also resulted in significant suppression of a P. xylostella population over 3 generations in the greenhouse test and 2 generations in the small cage experiment, suggesting that in places where immigration may be limited some long-term population suppression may occur. We suggest that Bt trap crops may be useful tools in situations where the cash crop may not be suitable or desirable for genetic engineering.