Evaluation Of Aphelinus Asychis Walker(hymenoptera: Aphelinidae) As A Biological Control Agent Against Myzus Persicea

The green peach aphid, Myzus persicea(Sulzer), is one of the most important pests on vegetables, and it widely distributes around the world. Currently, the chemical pesticides are still the mainly option to control M. persicae. Becaise of the disadvantage of using chemical pesticides, biological control becomes more and more useful in controlling of the green peach aphid. I studied the functional and numerical responses of Aphelinus asychis Walker, one of the most effective parasitoids of aphids. I described the life table parameters of A. asychis and M. persicea, then evaluated the control potential capability of A. asychis on M. persicae. The main results as follows:1. The functional responses of A. asychis on 2nd instar nymphs of M. persicaeThe numbers of predation and parasitism increased with the increase of host density. While the host density was set up as 50, the numbers of predation and parasitism were becoming flat, means with the increase of host density, the relative increase number were reducing. The results showed that the host density significantly affected the predation and parasitism abilities of A. asychis. The functional response could be described well by Holling type II model, and the correlation coefficient was more than 0.98. The instantaneous attack rate(a) of predation was 0.4045, the handling time(Th) of predation was 0.2238, the upper limit of predation was 4.5; The instantaneous attack rate(a) of parasitism behavior was 0.7525, the handling time(Th) of parasitism was 0.0340, the upper limit of parasitism was 29.4.2. The numerical responses of A. asychis on 2nd instar nymphs of M. persiceaThe total numbers of predation and parasitism increased with the increase of host density, the host density did not significantly affect the longevity of female adults and the numbers of predation behavior, but significantly affect the numbers of parasitism behavior of Aphelinus asychis Walker. The offspring of A. asychis from different host densities could complete their development duration, and the total development duration had no significant differences.3. The life table of A. asychis with different temperaturesWe studied the life table of A. asychis at 20oC, 25oC and 30oC, the results showed that temperature could affect the longevity of A. asychis. The development times of egg and larva, pupa, and the total development duration had significant differences at the three temperatures. The time of female adult stage was longer than the male, and at the different temperatures there were significant differences in the duration of female and male adults. The longevity of female wasp had a significant difference with the three temperatures, but had no significant difference among 25oC and 30oC. The longevity of female wasp was 42.5 day at 20oC, while 28.2 and 25.4 day at 25oC and 30oC. The longevity of male wasp was 33.9, 23.0 and 18.1day at 20oC, 25oC and 30o, respectively.According the results, temperature could also affect the fecundity of A. asychis. In different temperatures, the peak of oviposition appeared at different time, the fecundity of the peak are different, as well as the average fecundity per day. The fecundity of female adult was 13.5, 16.9 and 15.7 per day at 20oC, 25oC and 30o, respectively. The population fecundity was 8.8, 11.2 and 15.7 per day at 20oC, 25oC and 30o, respectively.Temperature could not significant affect the fecundity of A. asychis. The female wasp preyed 1.95, 2.04 and 2.03 aphids per day at 20oC, 25oC and 30o, respectively; the max predation quantity was 3.55, 3.56 and 3.86 at 20oC, 25oC and 30o, respectively; the total amount of predation of female adult was 93.57, 69.37 and 48.66 at 20oC, 25oC and 30o, respectively.Temperature could affect the life expectancy and reproductive value of A. asychis. The life expectancy of A. asychis reduced with the temperature increasing, and at different temperatures, the life expectancy has the same tendency of reducing with the aging of A. asychis Walker.4. Evaluation of control potential capability of A. asychis on M. persicae with life table methodWe compared the intrinsic rate of increase(rm), the net reproductive rate(R0), the finite rate of increase(λ), The mean generation time(T) and the doubling time(DT) of M. persicea and A. asychis at the three temperatures. The results showed that Ro of A. asychis was much higher than M. persicae at 20oC, 25oC and 30oC, respectively, and T of A. asychis was nearly twice of that of M. persicae at 20oC, 25oC and 30oC, respectively. It showed that during the time of a generation of Aphelinus asychis Walker, the peach aphid had fewer offspring than the wasp. The present study indicated that A. asychis could well control the population growth of M. persicae at different temperature in the laboratory environment.