Effect of Temperature on the Fitness of a Vip3A Resistant Population of <I>Heliothis virescens</I> (Lepidoptera: Noctuidae)

Abstract

Microbial insecticides derived from the soil bacterium Bacillus thuringiensis (Bt) have become increasingly important for pest management. In addition to crystal (Cry) insecticidal protein toxins formed during sporulation, vegetative insecticidal protein (Vip) toxins can be produced during the vegetative phase. Resistance to Cry toxins has been reported in laboratory- and field-selected populations of various Lepidoptera species and several studies have identified fitness costs associated with Cry toxin resistance. Here, fitness costs are examined in the first insect population to be reported with resistance to a Vip toxin, a laboratory-selected Vip3A-resistant subpopulation of the tobacco budworm, Heliothis virescens (L.) (Vip-Sel). The Vip-Sel population showed reduced survival to adult eclosion compared with an unselected subpopulation at all test temperatures, including the culture temperature (25 degrees C). Vip3A resistance was also associated with reduced egg viability and mating success and a lower intrinsic rate of population increase (r(m)) at temperatures below (20 degrees C) and above (30 degrees C) the optimal laboratory culture temperature. The latter findings agree with previous studies, that fitness costs associated with resistance are usually greater under stressful conditions. Such data can help predict the impact of fitness costs on the rate of development of resistance in the field and in the development of resistance management strategies that more fully exploit fitness costs.