A Study On The Biology And Its Control Function Of Aneristus Cceroplastae

Parasaissetia nigra Nitner is a kind of pest which has caused serious damage to rubber tree since 2004 in Yunnan. The effective approach available to prevent it from spreading is to nurture parasitoids. This research, based on the findings about the parasitoids of Parasaissetia nigra in Yunnan and Hainan Provinces, studied the biological behavior of the dominance parasitoid Aneristus ceroplastae and its control action to Parasaissetia nigra. Also, the toxicity of several major insecticides to Aneristus ceroplastae and Parasaissetia nigra was studied. The main results obtained were as follows:1.Morphological observation.The morphological characters of larvae and reproductive system of Aneristus ceroplastae were described in this paper. The dissection of Parasaissetia nigra and Aneristus ceroplastae showed that the larvae of Aneristus ceroplastae developed gradually through egg, 3 instars (the first stage larvae, the second stage larvae, the third stage larvae), pre-pupae, pupae and adult; the dissection of the reproductive system of just emergent female illustrated that the ovary of Aneristus ceroplastae consisted of 3 ovarioles on each side, and a mass of eggs were already developed in pupae.2. The biological behavior of Aneristus ceroplastae2.1 The selection of Aneristus ceroplastae to Parasaissetia nigra Parasaissetia nigra developing from second stage larvae to initial stage adult can be oviposited by Aneristus ceroplastae. But Aneristus ceroplastae couldn't oviposited in the first stage larvae.2.2 The individual development of Aneristus ceroplastae.The mean development time of Aneristus ceroplastae from egg to adult was 21～26d when host was the third stage larvae of Parasaissetia nigra at 26℃, among which, the time from egg to pupae was14～17d, the pupae was7～9d. The reproductive system of Aneristus ceroplastae started to develop at pupae: there were a few developed eggs in the 6-day pupae; the fecundity obviously increased in the 7-day pupae (63.9eggs on average). The fecundity of just emergent Aneristus ceroplastae was 154.65 eggs, after 24h the highest fecundity came (163.23 eggs). The statistics showed that most of the Aneristus ceroplastae eggs were developed at the pupae and just emergent stages. 2.3 The emergence of Aneristus ceroplastae.The adult parasitoid emerged with a peak at 8:00～10:00am. The emergence foramen lay by the anal cleft of host. It was round, measured at 0.2-0.6mm in diameter.2.4 The reproductive mode of Aneristus ceroplastae.The reproductive mode of Aneristus ceroplastae was sexual procreation. The adult Aneristus ceroplastae could mate as soon as being just emergent. The mating took 2～3 seconds. There was competition among males for mating. The valid mating stimulated ovarian oviposition. Under the same condition, valid mated females laid 82.0 times more eggs than virgin ones.2.5 The ovipositionThe major phases of oviposition of Aneristus ceroplastae were host searching, testing, inserting ovipositor, laying eggs and drawing out ovipositor. Aneristus ceroplastae couldn't tell whether the host had been parasitized or not, so it often laid eggs repeatedly in the host parasitized by conspecific parasitoids or even itself.3 Ecological characteristic3.1 The influence of temperature on the development and propagation of Aneristus ceroplastaeTemperature had significant effect on the development and offspring of Aneristus ceroplastae. With the increase of temperature from 18℃to 27℃, the developmental rates through various stages and generations quickened gradually, while the developmental rates got slower at 30℃. The binomial correlation between the temperature and the developmental rate of generation assumed V(e-a) = -0.0003T2 + 0.0185T - 0.2039. The developmental threshold temperature and effective accumulated temperature of various stages and generations were calculated at 12.76℃and 306.62 days-degrees. Accordingly, it can be estimated that Aneristus ceroplastae can finish 28-29 generations and 25-26 generations yearly in Hainan and Yunnan respectively.The body length of Aneristus ceroplastae were shortened with the increase of temperature. The body length of female of Aneristus ceroplastae was longest at 18℃(1.18mm) while at the 30℃was the shortest(1.03mm).The fecundity were 117.10 eggs,131.57 eggs,150.90 eggs,165.60 eggs and 44 eggs respectively at 18℃,21℃,24℃,27℃,30℃.The result showed that the fecundity was enhanced with the increase of temperature from 18℃to 27℃, while the fecundity was reduced at 30℃. The parasitism rates of Aneristus ceroplastae were lower at 18℃and 30℃. The Parasitic rate of Aneristus ceroplastae was highest at 21℃(36.0%), and the lowest (4.5%)at the 30℃.According as foregoing parameters, the temperature from 21℃to 27℃was suitable for development of Aneristus ceroplastae.3.2 The influence of photoperiods on the development and propagation of Aneristus ceroplastaeDevelopment of Aneristus ceroplastae was significantly affected by Photoperiods. With the increase of photoperiod, the development rates were quickened gradually. The mean development time from egg to adult was longest at L:D=10:14 (27.76d), and the lowest (24.83d)at the L:D=16:8.Photoperiods also had great influence on the fecundity and parasitic rates of Aneristus ceroplastae. The fecundity reached the highest at L:D=12:12 (150.9 eggs) , and the lowest (139.23 eggs) at L:D=16:8.3.3 The influence of temperature, photoperiods and humidity on the emergence of Aneristus ceroplastaeThe adult parasitoid emerged with a peak at 8:00～10:00a.m. Temperature, humidity and photoperiod all can affect its emergence. The increase of temperature from 18℃to 30℃quickened and concentrated the emergence of the adult of Aneristus ceroplastae; the rising of the humidity from 20% to 90% slowed the peak of adult emergence; and the shortening and lengthening of the photoperiod dispersed the time of it.3.4 The influence of temperature and food on the longevity of adult Aneristus ceroplastaeThe longevity of the adults was greatly affected by temperature and nutrition. With the increase of temperatures from 18℃to 30℃, longevity of female adults shortened gradually. Under the same condition, sort and concentration of nutrition can help to lengthen the longevity of them significantly. The adults fed by 10% sucrose solution had the longest life, while those fed by water only had the shortest life.3.5 The influence food and development time on the fecundity of adult Aneristus ceroplastaeThis study observed the fecundity of Aneristus ceroplastae by dissecting the adult Aneristus ceroplastae which had been fed 12h,24h,48h and 72h with different nutrition. It was found that food supply to and development of adult Aneristus ceroplastae did not have significant effect on their fecundity.4. The functional response and disturbance response of Aneristus ceroplastae to Parasaissetia nigraThe density of the host larvae - Parasaissetia nigra affected the parasitizing of Aneristus ceroplastae significantly, which accorded with the HollingⅡEquation: Na = 0.6721N / (1 + 0.0233N). The more host larvae provided, the more larvae were parasitized, but the increasing extent was getting smaller when the host density was no more than forty per Aneristus ceroplastae, while the increasing extent was getting much smaller when the host density was more than forty. Furthermore, the density of Aneristus ceroplastae also affected its own parasitizing which accorded with Hassell-Varley Equation E=0.3922P-0.5881. The more Aneristus ceroplastae provided, the less larvae were searched by parasitoids because of the interference among individuals.5. The influence of insecticides on the Aneristus ceroplastae and Parasaissetia nigraToxicity of 6 insecticides to Aneristus ceroplastae and Parasaissetia nigra was studied. The result showed that the order of selective toxicity was: deltamethrin>lambda-cyhalothrin>chlorpyrifos﹠cypermethrin>acephate>acetamiprid>Chlorpyrifos. Deltamethrin showed highest selective toxicity between Aneristus ceroplastae and Parasaissetia nigra and the lambda-cyhalothrin came second. The rest of four insecticides (chlorpyrifos, cypermethrin, acephate, acetamiprida) had no selection protection to Aneristus ceroplastae. It is recommended that deltamethrin should be selected to control Parasaissetia nigra during seasons when Aneristus ceroplastaea and other natural enemies are relatively numerous and lambda-cyhalothrin may be alternatively used.