Is resistance futile? Life-history costs of escaping parasitoid attack in a major crop pest.

Resistance evolution occurs when genetic variants that confer increased survival in the face of mortality causing factors (ie pathogens, parasites, and predators) increase in frequency within a population. It has profoundly shaped life on earth, but in the Anthropocene its implications for human health (antimicrobial resistance) and food security (pesticide resistance) are more widely discussed. Inegrated Pest Management strategies which integrate chemical control with the use of evolvable natural enemies such as parasitoid wasps have been designed to minimize resistance evolution in pests and protect food security. However, in recent years there have been more reports of pests becoming resistant to their biocontrol agents. In this study we investigate a potential emerging example of resistance to biocontrol in the glasshouse whitefly, Trialeurodes vaporariorum (Hemiptera: Aleyrodidae) Westwood, to the parasitoid wasp Encarsia formosa (Hymenoptera: Aphelinidae) Gahan. We found evidence for genetic variation in the whiteflies ability to survive parasitism based on quantitative genetic estimates of narrow-sense heritability derived from a family-level survival experiment. In a second experiment, we show that surviving parasitism attempts by Encarsia is costly for Trialeurodes; whitefly that were attacked and survived had lower fecundity and their eggs were less likely to successfully hatch compared to unexposed controls. We discuss the ways in which this life history trade-off between survival and reproduction when exposed to E. formosa could be exploited, for example by intercropping with suboptimal host plants, to maintain susceptible genotypes and slow resistance evolution.