Study On The Population Dynamics Of Eretmocerus Hayati And Control Efficacy To Bemisia Tabaci In Turpan Basin

In this paper, the population dynamics and the spatial distribution of Eretmocerus hayati as well as the control efficacy to Bemisia tabaci in Turpan basin werer studied. The key points are as follows:(1) There are significant differences between parasitic rates of Eretmocerus hayati to various instars whitefly nymphs(P<0.05). Parasitic rate of Eretmocerus hayati to 2nd instar nymph of whitefly was the highest at the density of 50 nymphs/leaf of B. tabaci from 1 pair to 5 pairs of parasitic wasp. The parasitic rates were 44.6%,50.6%,52.6%,52%, and 46.6%, respectively. Thus, the 2nd instar nymph of whitefly is the best period for the parasitic wasp.The parasitic effect of different densities of Eretmocerus hayati to different instar nymphs of B. tabaci showed that, the highest parasitic rate was observed in the treatment of 3 and 4 pairs of Er. hayati released at the density of 50 nymphs/leaf of B. tabaci, the parasitic rates reached to 52.6% and 52% to2 nd instar nymph of whitefly, respectively. And there were no significant differences between the parasitic rates to other instars. Thus, 3 and 4 pairs of Er. hayati released is the most suitable for the parasitic effect of the wasp. That is to say, the most suitable ratio of female adults : nymph of whitefly are 1:12.5-1:16.7.There werer significant differences for the emergence rate of. The highest emergence rate of the parasitic wasp adult was the 2nd instar nymph of whitefly parasitized by Er. hayati at 93.58%, followed by1 st instar, 3rd instar and 4th instar, the emergence rate were 85.51%,63.59% and 10.32%, respectively.(2) Eretmocerus hayati showed a typical follow-up and control pattern towards Bemisia tabaci based on the investigation. The parasitism rates of Eretmocerus hayati towards the nymph of Bemisia tabaci at the middle and lower part were significantly higher than upper part of cotton plants(p<0.05), which matches the lower-to-upper damage habit of the whitefly in the cotton field. Parasitism rate of Eretmocerus hayati to the whitefly on the west direction was significantly higher than the north direction in the northern area(p<0.05). No significant difference was found among directions of other areas. Aggregation indexes and Iwao linear regression analysis showed that Eretmocerus hayati presented aggregative spatial distribution in field conditions. This distribution pattern can be co-effected by the parasitoid's behavior and environmentfactors. Field sampling formula was built based on the Iwao sampling model: N=(4.2762/m*+2.2534)/D2.(3) The nymphs parasitized by Er. hayati were initially observed in 14 d after 5 times releasing of the parasitic wasp adult. The highest parasitic rate reached to 31.4% in the green houses of tomato, and the decrease rates of B. tabaci adults and nymphs were 78.17% and 75.45% after the parasitic wasp adult released 49 d, respectively. In the mean time, The highest parasitic rate reached to35.94% in the green houses of pepper, and the decrease rates of B. tabaci adults and nymphs were 83.38% and 83.87% after the parasitic wasp adult released 56 d, respectively. Thus, Er. hayati showed significant effect in the control of B. tabaci in green houses.