Low intrinsic rate of natural increase in BT-resistant population of Diamondback Moth, Plutella xylostella (L.) (Lepidoptera: Yponomeutidae)

Abstract

BT-resistant (KR) and BT-susceptible (KS) Diamondback Moth populations were produced in the laboratory from a BT-resistant natural population in watercress greenhouse in Kishiwada, Osaka Prefecture. The two experimental populations were fed on three diets: artificial diet, radish seedlings, and watercress, and reared in a room at 25°C and 16L : 8D. The LC50 for a BT formulation (Toarow® CT) for KR and KS was 25,200 and 1.14 ppm, respectively. KR showed lower hatchability, longer duration and lower survival rate in the larval and pupal stages on all the three diets, together with shorter adult longevity and lower fecundity than KS, suggesting much lower fitness and intrinsic rate of natural increase, than KS. The trade-off between BT-resistance and fitness (particularly delayed adult emergence) may explain the quick elimination of BT-resistant moths from a mixed population including both BT-susceptible and BT-resistant moths.