Movement and survival of diamondback moth (Lepidoptera: Plutellidae) larvae in mixtures of nontransgenic and transgenic canola containing a cryIA(c) gene of Bacillus thuringiensis

Knowledge about the movement and survival of diamondback moth, Plutella xylostella . (L.), in mixtures of nontransgenic and transgenic canola, Brassica napus (L.), containing a synthetic cryIA(c) insecticidal gene from the bacterium Bacillus thuringiensis Berliner would have implications in designing resistance management strategies. In diamondback moth larval movement studies neonates moved 72 h after infestation and other instars moved within 24 h. Diamondback moth larval movement and survival were studied in pure stands and mixtures of 80:20, 60:40, 40:60, and 20:80 transgenic and nontransgenic canola plants, respectively, that were arranged in rows within cages in a greenhouse. On the 6th d, no larvae survived in the pure stand of transgenic canola, and few survivors were recorded on transgenic canola plants in mixtures. In mixtures, the percentage of adult emergence decreased as the proportion of transgenic plants increased. All 4 instars were killed when they fed exclusively on transgenic plants. None of the 2nd, 3rd, and 4th instars were able complete their life cycle when they fed on transgenic canola plants for 48 h and were subsequently transferred to nontransgenic plants. The results suggest that in seed mixtures diamondback moth larvae would move from transgenic to nontransgenic plants before acquiring lethal doses of toxin, indicating a higher possibility of resistance development. These results suggest that a seed mixture strategy may not be an effective strategy against diamondback moth to prevent or reduce the rate of resistance development against transgenic canola. However, transgenic and nontransgenic plants could be grown in separate rows with a wider row spacing (strip planting) to minimize the rate of resistance development.