Interspecific Competitions Among Three Major Papasitoids Of Plutella Xylostella(l).

Diamondback moth, Plutella xylostella, is one of the major pests of crucifer vegetables. The lack of effective natural enemies has resulted in widespread damage by this pest in many countries. None of its parasitoids can individually keep P. xylostella in check. Studies on interspecific interactions among and evaluation of the joint control potential of the parasitoids will provide the fundamental information for biological control of P. xylostella. This study was conducted to investigate the interspecific interactions among three major parasitoids of P. xylostella: Cotesia plutellae, Diadegma semiclausum and Oomyzus sokolowskii. The major results are summarized as follows.1. Interspecific interaction between C. plutellae and D. semiclausumParasitization of host larvae by D. semiclausum was not affected significantly after the host larvae had been parasitized previously by C. plutellae, and that by C. plutellae was not affected significantly after the host larvae had been parasitized previously by C. plutellae, either. When host larvae were exposed to D. semiclausum immediately after parasitized by C. plutellae, or exposed to C. plutellae immediately after parasitized by D. semiclausum, most of them produced C. plutellae adults and only a few of them produced D. semiclausum. When host larvae were exposed to D. semiclausum at the 2nd day or 3rd day after parasitized by C. plutellae, all host larvae produced C. plutellae adults. When host larvae were exposed to D. semiclausum at the 4th day or 6th day after parasitized by C. plutellae, both parasitoids sharing the same host could develop in the host larvae until C. plutellae larvae egresses to pupate. The remained D.semiclausum larvae died in those larvae due to dry of the host. However, no parasitoid adults were produced when host larvae were exposed to C. plutellae at the 2nd day after parasitized by D. semiclausum., and some D. semiclausum cocoon were produced when host larvae were exposed to C. plutellae at the 4 th day after parasitized by D. semiclausum.2. Interspecific interaction between D. semiclausum and O. sokolowskiiParasitization of host larvae by O. sokolowskii was not affected distinctly after the host larvae had been parasitized previously by D. semiclausum, and that by D. semiclausum was not affected distinctly after the host larvae had been parasitized previously by O. sokolowskii, either. When host larvae were exposed to O. sokolowskii after parasitized by D. semiclausum, the wasps produced were substantially D. semiclausum adults. When host larvae were exposed to D. semiclausum after exposed to O. sokolowskii, the ratio of hosts produced O. sokolowskii increased and that produced D. semiclausum decreased with the increasing tune interval between the two exposures.3. Interspecific interaction between C. plutellae and O. sokolowskiiParasitism of host larvae by O. sokolowskii was reduced drastically when host larvae parasitized previously by C. plutellae were exposed to O. sokolowskii, but parasitization by C. plutellae was not. affected distinctively when the host larvae were first exposed to O. sokolowskii and then to C. plutellae. When host larvae were exposed to O. sokolowskii immediately or at the 1st, 2nd, 3rd day after parasitized by C. plutellae, they produced C. plutellae, no O. sokolowskii. However, when host larvae were exposed to O. sokolowskii at the 4th or 6th day after parasitized by C. plutellae, O. sokolowskii could parasitized the larva of C. plutellae developing inside host larva to form hyperparasitism. The host larvae produced substantially C. plutellae when they were exposed to C. plutellae immediately or at the 1st day after exposure to O. sokolowskii, and died during their developing course when they were exposed to C. plutellae at the 2nd dayafter exposure to O. sokolowskii. However, when host larvae were exposed to C. plutellae at the 3rd day after exposure to O. sokolowskii, they produced O. sokolowskii, no C. plutellae.Qingbao Li Directed by Prof. Zuhua Shi...