Chemical ecology of two co-occurring Lygus species on shared host plants

Background/Question/Methods   Both generalist and Hemipteran insects are understudied in terms of their chemical ecology even though many are major agricultural pests. A greater understanding of chemical cues that mediate interactions among plants, Hemipterans, and their natural enemies would contribute to a basic understanding of plant-insect interactions, and would benefit biological control efforts. Here we took a comparative approach to examine interactions among two species of generalist Lygus bugs (Hemiptera: Miridae), and common agricultural and weedy host plants. One species, Lygus lineolaris, has a broad range throughout the eastern U.S. and is a serious agricultural pest on alfalfa, cotton, and many fruit crops. The second species, Lygus rubrosignatus, co-occurs with L. lineolaris on many hosts, but is not considered a target of pest control measures. However, both species are attacked by parasitoid wasps in the genus Peristenus that were introduced from Europe to control L. lineolaris in the U.S. Volatile organic compounds were collected from alfalfa and sweet clover with and without the damage from Lygus bug feeding using a push-pull collection system. Volatile blends from the two species of plants, as well as those induced by the two species of insects at different life stages were compared using Principle Component Analysis (PCA).

Results/Conclusions   Our experiments demonstrate that both Lygus lineolaris and Lygus rubrosignatus induce distinct and characteristic volatile blends when feeding on different legume host plant species (alfalfa – Medicago sativa and sweet clover – Melilotus officinalis). Additionally, we found that nymphs of both of these Lygus species also induce volatile blends that are distinct from adult blends of conspecifics and heterospecifics. These different treatments (adults and nymphs of the two species each represented on the two legume hosts) cluster with other members of that treatment in a PCA, and cluster distinctly from members of other treatments and controls. An examination of total volatiles and diversity of volatiles using univariate statistics demonstrates that both quantity and quality of volatile blend varies among the treatments and contributes to the separation observed in the PCA. The differences in these blends on commonly utilized cultivated and weedy hosts have important implications for host finding by Peristenus wasps and control of the target pest, Lygus lineolaris.