Mother always knows best. This paradigm has permeated studies on plant-insect interactions for the better part of a half century, and postulates that adult female insects should prefer to oviposit on host-plants that promote survival and growth of their young. Under field conditions, however, researchers sometimes struggle to correlate larval performance with female oviposition choice. Ecological factors such as top-down pressure from natural enemies can obscure the relationship, leading to alternative patterns of host plant use. Here, I investigated the preference-performance relationship and tritrophic interactions involving Manduca sexta (Lepidoptera: Sphingidae), their natural enemies, and plants in the Solanaceae. Despite being among the most highly studied model insects in the world, the natural history and preferences of M. sexta across their preferred plant family, surprisingly, are poorly documented. To determine if adult food plant preference correlated with larval performance, given variation in natural enemy pressure, I evaluated patterns of host plant use of M. sexta in a common garden containing plants across the Solanaceae. Then, through targeted laboratory manipulations, I tested the degree to which natural enemy pressure explained these observed field patterns.
Results/Conclusions
Hawkmoths overwhelmingly preferred plants in Nicotiana and Datura compared to Capsicum, Physalis, and Solanum. Further, the laboratory preference rankings among plants paralleled field observations, illustrating that oviposition preference is not affected by plant size. Overall, the most preferred plants for adult female oviposition were inversely correlated with plant species that provided the best growth for natal offspring. These results imply that this negative preference-performance relationship is maintained in part because by utilizing these noxious food plants M. sexta garners protection against natural enemies in the environment, specifically parasitoids. Even though the proportion of parasitism between tobacco and tomatoes in the field was not significantly different, and hornworm preference correlated with parasitized hornworm abundance, laboratory rearing of hornworms parasitized with C. congregata showed wasp survival to be significantly higher on S. lycopersicum than Nicotiana sp. This work coincides with others findings and adds to the body of knowledge documenting a negative relationship between oviposition preference and physiological performance in the Lepidoptera as a means for defense and protection against natural enemies in the environment.