Symbiotic rhizobia impact pea leaf weevil (Coleoptera: Curculionidae) feeding and oviposition on legumes

Legume-rhizobia symbioses are host-specific interactions that affect host nutrient levels and defences by enhancing nitrogen fixation. These changes to host quality can affect the susceptibility of plants to below and above-ground herbivory. Pea leaf weevil, Sitona lineatus, is an oligophagous insect herbivore of legumes. Adults feed on foliage while larvae feed on root nodules. It is a major pest of the legume crops, field pea (Pisum sativum) and faba bean (Vicia faba). We investigate the influence of rhizobia symbioses on pea leaf weevil feeding and oviposition on legumes. We conducted a no-choice greenhouse assay to investigate adult host acceptance and larval development on seven different legumes inoculated with corresponding host-specific rhizobia strains. We also tested the effects of rhizobia and nitrogen on pea leaf weevil host preference and oviposition on faba beans in a field choice study. The legume-rhizobia association drives pea leaf weevil larval development, but not adult host acceptance. Adults feed on reproductive hosts and on all of the tested legumes except chickpeas and minimal feeding was observed on lentils. Field pea and faba bean support larval development and soybean is an occasional host to larvae. Weevils preferred control plants compared to rhizobia-inoculated faba beans. Rhizobia resulted in increased nodulation and protection of faba bean reproductive output. Nitrogen amendment did not protect faba bean reproductive output from pea leaf weevil feeding damage, even though it decreased larval development and root nodulation. Our study shows that legume-rhizobia symbiosis can influence legume interactions with above and below-ground herbivores.