A novel level of interactions in plant–insect systems

Abstract

The importance of variation in the ability of individuals to survive or perform on different types of resource (implicit in evolutionary studies) has been discussed in both host–parasite¹ and plant-insect systems^2–4. But variation in host-choice behaviour and its interaction with offspring performance on variable resources⁵ has been studied only in insect populations that each use several plant species^6,7. Here I show that in a natural population of the butterfly Euphydryas editha (Nymphalidae), some females are specialized in both oviposition behaviour and offspring performance. These specialists prefer to lay eggs on certain individuals of the host plant Pedicularis semibarbata (Scrophulariaceae) that also improve the survival of their offspring. Other E. editha females in the same population are not so specialized. They show no oviposition preference among individual P. semibarbata, and survival of their offspring is not correlated with the plant suitability categories defined by the specialists. Thus information vital to understanding the true nature of the interactions in a plant–insect system is lost when the process is described using either the average ability of an insect population to exploit a plant population or the average ability of a plant to resist attack by an insect species.