State and experience dependent plasticity in feeding preference of pea leaf weevil (Coleoptera: Curculionidae)

Background/Question/Methods

Phenotypic plasticity is the ability of one genotype to produce multiple phenotypes in response to changing environmental conditions. This is one way that organisms maximize fitness under dynamic environments. State-dependent plasticity helps herbivores use resources when they are physiologically capable. Experience-dependent plasticity allows herbivores to use prior-host experience to minimize risk in host selection. Host plant choice is crucial for specialist herbivores that need to access specific host plants at certain phenological stages. The pea leaf weevil, Sitona lineatus, is an oligophagous insect herbivore that feeds on leguminous plants. Adult weevils feed on the foliage during different reproductive states in a one-year life cycle. Adults feed on primary hosts, field pea and faba bean, that support larval development and on secondary hosts that do not support larvae. In this study, we investigate how reproductive state and prior-experience modulate host finding behaviour in the pea leaf weevil. We conducted a laboratory two-way choice study to test the effect of the reproductive stage on pea leaf weevil feeding preference between two primary host plants, field pea and faba bean. Another three-way choice study tested the effect of prior experience on subsequent host preference among two primary hosts and the secondary host, alfalfa.

Results/Conclusions

Pea leaf weevil host preference is state-dependent. Reproductive weevils exhibit a preference for faba bean over field peas, while reproductively inactive weevils show no preference between primary hosts in the two-way choice study. This preference for faba bean is adaptive, as more pea leaf weevil larvae are supported on faba bean. Reproductive individuals fed more compared to non-reproductive individuals. Prior-host experience affected host preference in reproductive individuals but not in non-reproductive individuals in the three-way choice study. Reproductive females fed more on field pea and faba bean compared to alfalfa only when fed on field peas prior to the experiment. Non-reproductive weevils fed more on primary host plants compared to the secondary host despite the experienced host. This study suggests that oligophagous insects can show phenotypic plasticity in host preference to maximize fitness benefits in the absence of secondary host plants and prior-host experience differentially affected host preference at different reproductive stages.