Study On Superparasitism Of Encarsia Sophia And Influence Of Superparasitism On Offspring

In this paper, the main research object is Encarsia sophia(Girault & Dodd), a kind of important natural enemy parasitoids of Bemisia tabaci (Gennadius). First, we studied how to locate the nymph of B. tabaci and how to determine the occurrence of superparasitism, then we explored superparasitism of Encarsia sophia and its influence on parasitoid offspring development, the demarcation development stage of host nymph for thelygeny and arrhenogeny and the influence of host density and inoculation time on the superparasitism rates.According to the observation that the nymphs of the whitefly would not move after the late first instar nymphs begin to feed, a method of using digital camera to take photos of host leaf with nymphs and printing the photos on A4 paper was used to mark the locations of the nymphs on host leaf. Furthermore, we observed the morphologic change of nymphs and investigated the relationship between the body size and the instars of B. tabaci nymphs by using this method. The results indicated that there were significant differences among the first instar, the second instar, the third instar and the early fourth instar nymphs both the body length and width of B. tabaci nymphs, and the coefficient of variation of nymphs body size increased with the larva instars increased. So we could distinguish different instars according to their body size and morphology.We observed thelygeny parasitic behavior of Encarsia sophia using dissecting microscope and petri dish as arena, and explored the relationship between the parasitization times of E. sophia and the number of eggs loaded in host, the relationship between the parasitization times of E. sophia and thelygeny behavior, the influence of the superparasitism on female offspring development, the influence of parasitic time intervals on competition of offspring and the occurrence rate of superparasitism. At last, we can determine whether E. sophia really oviposited host through observing its parasitical behavior. In addition, the detection time of E. sophia in vivo of nymphs of whitefly and the number of eggs loaded per host increased significantly by the parasitic times, the detection time of E. sophia in vivo of nymphs of whitefly prolonged from 147.37±8.41s for one parasitization to 285.43±32.82s for three parasitizations, and the number of eggs loaded per host increased from the average of 1.04±0.03 for one parasitization to 3.05±0.08 for three parasitizations. The development time of offsping also prolonged significantly with the parasitization times increased. The total development time of E. sophia offsping prolonged obviously from 11.53±0.11d for one parasitization to 15.53±0.41d for three parasitizations. The thelygeny superparasitism rates of Encarsia sophia decreased sharply with the time interval of oviposition, The thelygeny superparasitism rates of Encarsia sophia decreased from 70% of the oviposition time interval 0-12 h to 23.8%. Moreover, there were obvious competition relationship among the parasitoids in host, both the primiparity offsping or the supernumerary larva can survive after competition before 48h of the time interval of oviposition, but all the primiparity offsping would defeat the supernumerary larva after 48h of the time interval of oviposition.We observed arrhenogeny behavior of Encarsia sophia and compared it with thelygeny behavior. We also studied the demarcation point of thelygeny and arrhenogeny, The results indicated that the thelygeny behavior and arrhenogeny behavior could be distinguished through naked eyes, and the demarcation development stage for arrhenogeny was 5 days after thelygeny happened.We studied the influence of E. sophia of different inoculation times and exposure period on superparasitism ratio in experiment. The results showed, both inoculation times and exposure period significantly influenced superparasitism of E. sophia. The superparasitism ratio increased from 0.4±0.4 (%) of inoculation time 1 (1 female/12 h) to 47.6±2.3 (%) of inoculation time 3 (5 females/12 h), and increased from 11.2±2.0 (%) of exposure period 1(6 h/ 3females) to 39.6±2.9 (%) of exposure period 3(24 h/3 females).