Sex Assignment And Parasitical Adaptationof Anastatus Disparis(Ruschka)(Hymenoptera: Eupelmidae)

Lymantria dispar(Linnaeus) is an important international quarantine forest insect pest, which attacks both conifer and broad leaved trees. Anastatus disparis(Ruschka) is an important egg parasitoid of several noxious Lepidoptera species, including L. diapar.The relationship between the development of egg to adult of A. disparis and environmental temperature, and the relationship between the sex ratio of offspring and environmental temperature, were studied at five different environmental temperatures by using eggs of Antheraea pernyi as the substitute host. Result showed that the effective accumulated temperature of A. pernyi male(290.15±3.48 day degrees) was lower than that of female(338.88±3.66 day degrees). The developmental threshold temperature of male and female were all around 13 ℃. There were no significant differences in sex ratios of offspring and different environmental temperatures.The relationship between the daily sex ratios of offspring and the age of females were studied by counting the daily sex ratios. Result showed that whether females were mated or not did not affect the total number of offspring produced by them. The daily sex ratios of offspring from mated female was significantly negative-correlated with the age of female.In order to study the relationship of offspring body size developed from different host species and host body sizes, the body length of different host species and hind tibia length of wasp offspring from different host species were measured. Result showed that both the male and female could finish their development in different host species with different sizes. There was a linear relationship between host length and wasp offspring sizes developed from different host species.In order to study the sex assigned mechnism influenced by the maternal eclosion experience, the sex ratios of parasitoid offspring from Antheraea pernyi egg and Dictyoploca japonica Moore egg(or eri-silkworm egg), which were parasitised by the female emerged from Dictyoploca japonica Moore egg and eri-silkworm egg,were compared. Result showed that male proportion of offspring parasitoid developed from D. japonica eggs parasitized by female from D. japonica egg was found to be significant lower than that male offspring developed from D. japonica egg parasitized by female from A. pernyi egg, but there was no significant difference for the male proportion of parasitoid offspring from A. pernyi egg parasitized by female from A. pernyi egg. Male proportion of parasitoid offspring from eri-silkworm egg parasitized by female from eri-silkworm egg was found to be significant lower than that male offspring from eri-silkworm egg parasitized by female from A.pernyi eggs, but was significant higher than that male offspring from A. pernyi egg parasitized by female from A. pernyi egg. Male proportion of offspring decreased when the female parasitized the host which was same with the female emerged from. This adaptive change may help the parasitoid population development in nature.In order to study the sex assignment mechnism influenced by the parasitoid parasitical experience, the sex ratios of offspring from different host species(A. pernyi egg and D. japonica egg) parasitized by female developed from A. pernyi egg and D. japonica egg with different orders, were compared. Results showed that male parasitoid proportion from D. japonica egg parasitized by female from A. pernyi egg and D. japonica egg with parasitical experience on A. pernyi eggs was significantly higher than that male wasp developed from D. japonica egg parasitized by female from A. pernyi egg with no parasice experience. Male parasitoid proportions developed from D. japonica eggs parasitized by females from A. pernyi eggs and D. japonica eggs with parasice experience on A. pernyi eggs were no significant difference. Parasitical experience might hinder or reduce female’s memory of eclosion experience. For the sex assignment influenced by the parasitical experience, if the female parasitized bigger host first then the smaller host, female could adjust the offspring sex ratio in the smaller host by the experience with the bigger host. In the “host size model”, the phenomenon that more male offspring developed from small size host could be explained by our result that more male offspring developed from D. japonica egg parasitized by female with parasitical experience on A. pernyi egg.In order to explore the reason that the parasitoid offspring from the L. dispar egg were all male, correlation between different host sizes and sex ratios of parasitoid offspring developed from different host species parasitized by female from A. pernyi egg was analyzed and established. Result showed that there was a reciprocal equation between the host size and sex ratio of offspring. The equation is Y= 14.652-16.451/ X(x is host size, Y is the sex ratio). When the offspring were all male(Y=0), the host size(x) would be 1.189, which is bigger than the size of L. dispar egg. Therefore, this result could explain the phenomenon that the parasitoid offspring developed from the L. dispar eggs were all male. However, by means of special designed methods, we can obtain the female offspring from the L. dispar eggs by two ways: parasitoid female from the A. pernyi egg parasitize the L. dispar egg mass covered by the fur from their materanl adult or the shell of A. pernyi egg. Whatever, the female offspring proportion was significant lower than that male offspring developed from A. pernyi eggs.Sex ratio could be regard as a reference index when we studied the adaptability of A. disparis in the different host species. The change pattern of offspring sex ratios from the different host species was studied. A. disparis developed from the suitable host had the ability to parasitize unsuitable host, but it is hard to adapt the unsuitable host(all the offspring from the unsuitable host was male). A. disparis developed from the unsuitable host could adapt to the suitable host rapidly. A. disparis population from the L. dispar egg in the field might come from the L. dispar egg mass parasitized by other A. disparis population emergen from the bigger host species.The phenomenon of hyperparatization of A. disparis can be observed when the hosts were scare. In order to study the competition of several eggs in one host, we control the entering order of male and female eggs into one host. Quantities of the male and female eggs in one host were also set by control the parasitical time of the mated and unmated female. Results showed that the offspring sex was influenced by the sex of the egg which firstly entered into the host. It might be a kind of adaptation consequence of avoiding waste of host resource.