Ecology and management of Lygus and the distribution and species composition of Peristenus spp. in Washington.

摘要

Lygus hesperus Knight (Hemiptera: Miridae) is the perennial key direct pest in alfalfa seed production in the western US. Lygus populations left uncontrolled reduce seed yields and quality. Lygus spp. may colonize alfalfa fields from non-agricultural habitats and host plants adjacent to fields. We investigated if candidate host plants found in non-crop areas near alfalfa seed fields allowed reproduction and nymphal development by L. hesperus. Canada thistle ( Cirsium arvense Scop.) and stinging nettle (Urtica dioica L.) were the plants that Lygus were able to complete their life cycle on more frequently than other plants evaluated. In a diverse agricultural landscape such as the Columbia Basin of central Washington, plants that are found in non-crop areas are not the only potential source for pest insect refuge. As such, several cover crop blends were evaluated for their potential to serve as host sources for Lygus. The highest numbers of Lygus spp. were collected from alfalfa ( Medicago sativa L.) and northern birdsfoot trefoil (Lotus corniculatus L.), plots whereas very few were collected from perennial ryegrass (Lolium perenne L.) plots. This information could be quite useful to serve as an information guide in cropping systems where Lygus is a major pest and where integrated pest management plans are being implemented. An important parasitoid of Lygus in Washington state is the wasp Peristenus howardi Shaw (Hymenoptera: Braconidae) and its congener species. Here we report parasitism rates of Lygus in alfalfa seed production and other habitats in Washington state, and provide preliminary methods to identify Peristenus spp. from larval parasitoids obtained in parasitized nymphs of Lygus . We collected Lygus nymphs from sites throughout southeastern Washington State to determine parasitism rates by Peristenus spp. in alfalfa seed and other crops. Over 15,000 Lygus nymphs were collected, and dissected to determine parasitoid presence in different geographic regions and on different host plant species. The dissections yielded small larval parasitoids that were not identifiable morphologically to species level. Therefore, we used PCR to amplify a region of the mitochondrial cytochrome oxidase 1 gene for species identification. We identified three species of Peristenus from Lygus nymphs in our samples.