Biological Control Of Western Flower Thrips Frankliniella Occidentalis And Spider Mites Tetranychus Truncatus By A Shared Predotory Mite Neosoiuls Barkeri (Hughes)

The predatory mite, Neosoiulus barkeri(Hughes), is a generalist mainly preying on spider mites and thrips, etc. This mite predator gets widely used in Agricultural bio-control for its wide range of prey, strong predation and simple artificial culturing. We studied the capacity of one species of predator to control two major pests of greenhouse crops, Western flower thrips (Frankliniella occidentalis Pergande) and the spider mite (Tetranychus truncatus) in a cucumber-one-predator-two-prey system. The possibility for biological control of spider mites and thrips by a shared predator in a greenhouse was discussed. The main results are as follows:1. The foraging abilities of N. barkeri for spider mites prey Tetranychus truncates, thrips prey Frankliniella occidentalis and mixed prey of two species were investigated by a series of release-recapture experiments in a greenhouse. The results showed that when released inside a circle of hexogen with the six apex occupied by cucumber plants that were alternately clean or infested with either of single species of prey or mixed prey, the predatory mites were recaptured significantly more on infested plants than on clean plants. This suggested that N. barkeri had stronger searching abilities on its prey, and could accurately locate the infested plants no matter with T. truncatus, F. occidentalis or mixed prey.2. The oviposition rate and predation rate of N. barkeri was measured on three different diets:spider mite, young first instars thrips and a mixture of spider mite and young first instar thrips in laboratory. It was showed that a higher juvenile survival and developmental rate could be observed on a mixed diet than on either of single pest diet and suggested that the mixed diet was helpful to the development of the predator through a positive effect of mixed diets on predator population.3. We evaluated the control efficacy of the predatory mites N. barkeri(Hughes) in cucumber crops in greenhouse with only spider mites, only thrips or both herbivors together. We found significantly highest abundance of the shared predators and lowest levels of either of the two herbivore species when offered with both herbivors. There was no effect of the presence of thrips on spider mites densities. However, control of thrips was improved by increasing the predation rate by predator in the presence of spider mites. Thus, apparent competition happened in such a one-predator-wo-prey system. Laboratory experiments suggest that this was due to a higher juvenile survival and developmental rate on a mixed diet. Hence, better control could be achieved not only because of apparent competition, but also through a positive effect of mixed diets on predator population.4. The vertical distribution of spider mite, thrips and their shared predator showed that all of them located much more on middle part of the plants than on other position of the plants. This suggested that the predators could follow their prey effectively and further explain that the biological control of Western flower thrips F. occidentalis and spider mites T. truncatus could be achieved by a shared predotory mite N. barkeri.