Host plant acceptance and pea leaf weevil, Sitona lineatus (Coleoptera: Curculionidae) development in response to rhizobium-field pea symbiosis

Pea leaf weevil (Sitona lineatus L.) is a major pest of field peas and faba beans (Fabaceae). Economic damage to these legumes is caused by S. lineatus adults and larvae that feed on foliage and the rhizobia-containing root nodules, respectively, thereby causing reduced plant nitrogen and crop yield. The rhizobia-plant interaction may affect pea leaf weevil herbivory and development by influencing plant food quality and chemical defense. We tested the hypothesis that Rhizobium-field pea interactions influence S. lineatus foliar feeding, larval development, and field pea yield. Field pea plants received one of four treatments in each of three experiments assessing foliar feeding, larval development, and yield: 1) inoculated with the wild-type Rhizobium leguminosarum, WT3841; 2) inoculated with a mutant R. leguminosarum, MT3940 that does not fix nitrogen; 3) treated with nitrogen; and 4) control plants that received only water. After 5 weeks, male and female S. lineatus were introduced into each pot containing the variously treated plants and were allowed to feed for 4 days. There was no treatment effect on adult S. lineatus herbivory, which could be due to a trade-off between nutritional food quality and chemical defense. The wild-type Rhizobium strain, however, significantly supported field pea yield, and S. lineatus development from egg to adult stage compared to the mutant-type, and other treated plants. Lower crop yield and development of S. lineatus on plants inoculated with the mutant-type, MT3940 could be due to smaller nodule size and a lack of fixed nitrogen compared to wild-type, WT3841 treatment.