TRADE-OFFS WITH RESISTANCE TO A GRANULOSIS-VIRUS IN THE INDIAN MEAL MOTH, EXAMINED BY A LABORATORY EVOLUTION EXPERIMENT

1. When microbial agents are used as pest-control agents, resistance in the host may be selected for. If resistance occurs there are potentially fitness costs due to trade-offs between resistance and other life-history traits. Genotypic trade-offs with resistance to a virus in a lepidopteran host are examined by a micro-evolutionary selection experiment. 2. Six populations of the Indian meal moth, Plodia interpunctella, were established, three of which supported a granulosis virus infection (selected insects) while the remaining three acted as virus-free controls. 3. After a period of 2 years, bioassays with the virus showed that selected moths were 1.96-fold more resistant to infection (LD50S) than those derived from the virus-free control populations. 4. Correlated with this increase in resistance were a lengthening of development time, a reduction in egg viability and an increase in pupal weight. 5. These changes in life-history traits suggest that a cost in fitness of 15% (sensu Sibly & Calow 1986) is associated with the evolution of the resistance. 6. The importance of fitness costs associated with the development of resistance to pathogens is discussed.