A Study On The Biology And Its Utilization Of The Braconid, Microplitis Pallidipes

Beet armyworm, Spodoptera exigua Hübner (Lepidoptera: Noctuidae) is one of worldwide polyphagous insect pest. It outbreaks frequently all over the world and have caused high level of economic damage. One of the important reason for runing rampant of this pest is that the resistance of beet armyworm to most of insecticides due to incorrect use of insecticide for a long time. So it is difficult to control beet armyworm in chemical measure. In order to find out efficient measures to control beet armyworm, the biology of M. pallidipes is studied under laboratory conditions. We also have studied the effect of M. pallidipes on beet armyworm, and the toxicity of some insecticide to M. pallidipes. The following are results:Mythimna separata Walker is a suitable host for M. pallidipes when massive rearing in laboratory condition: M. pallidipes can parasitize M. separata and develops its larval stage in successfully. The parasitism usually occurrs on the larvae with 1st~3rd instars and the larvae of the 4th instar is hardly found the parasitism by the parasite. In the experiment, the developing period of M. pallidipes showed no significant difference among the different stages of the host larvae. But the weight of cocoon bred in 3rd instar of the larvae was the heaviest comparing with those bred in 1st, 2nd and 3rd instars of the larvae. The parasitizing rate and pupae weight which were bred in the larvae of the 1st instar were the lowest but the mortality rate after parasitizing was the highest. Furthermore, M. separata could be kept in laboratory easily without cannibalism habitant. It indicates that the larvae of M. separata during their 2nd ~3rd instars are the suitable host when rearing M. pallidipes under laboratory condition.The dynamics of parasitism of M. pallidipes: The parasitized rate was increased with the stings by the parasitoid. The parasitizing rate with one sting, two bout of sting and three bout of sting were 65.13%( N=255), 84.21%(N=125) and 100%(N=124),respectively. The times of sting by M. pallidipes were no significant influence on its own development period. But the weight of the pupae in the host with one sting was the heaviest. The host larvae about 223.5±24.78 could be parasitized by one femal M. pallidipes on average. The...