Western flower thrips (Frankliniella occidentalis) and other species
Pest description and crop damage Thrips are minute, slender bodied insects (0.5 to 1.0 mm in length). Wings may be present or absent and are unlike normal insect wings; thrips wings are essentially thin rods lined with long hairs. Thrips feed on leaves by rasping plant cells and sucking out their contents. Thrips feed on leaves and flowers, but they prefer the underside of leaves. Use of a hand lens or magnifying glass will aid in their detection and identification.
Biology and life history Thrips have a complex life cycle in which the last two immature stages are hidden and non-feeding. During the growing season, there are many overlapping generations, with a substantial portion of the population at any given time in one of the non-feeding stages, largely protected from pesticides and other management tactics. This, and the fact that thrips eggs are laid inside plant tissue, makes thrips very difficult to control since they rebound quickly as new adults and nymphs emerge daily from these hidden places.
Scouting and thresholds Monitoring for thrips is important because catching a population build-up early is necessary to achieving effective control. There are no established thresholds or scouting techniques for thrips in hemp. Beating sheet/tray technique can detect thrips, but it is unclear how accurately this sampling can estimate population size.
Thrips are food to many generalist predators, especially Orius spp., and just as in the case of aphids, preservation of predatory insects and spiders via careful use of insecticides can reduce the risk of damaging thrips populations.