Oviposition Decisions In Response To Conspecific Competition In Sclerodermus Guani Xiao Et Wu(Hymenoptera:Bethylidae)

Sclerodermus Xiao et Wu(Hymenoptera:Bethylidae)is a parasitic natural enemy of stem-boring coleopteran pests in forests,including long horn beetles,is widely used in biological control of forest insect pests in China mainland.So far,numerous qualitative studies have been carried out,focusing on bionomics,life history and control applications.However,researches on its behaviors are limited.In order to understand oviposition decisions in response to conspecific competition in guani,my thesis focused on oviposition behavior of S.guani in response to eggs laid by other fundresses and the presence of other fundresses.This study provides data for understanding cooperative host exploitation in Sclerodermus parasitoids,and offer as well relevant information for the mass-production of the parasitoid in biological control practices.1.Oviposition decisions of Sclerodermus guani in response to eggs laid by conspecificsTo examine the effect of kinship between foundresses on cooperative parasitizing behavior,groups of two sibling or non-sibling foundresses were compared in oviposition and offspring development on Tenebrio molitor host pupae.The following results were obtained.(1)The number of the 1st foundress eggs interacted with the kinship between the two foundressses in affecting the number of eggs laid by the 2nd foundress,which increased with the number of the number of eggs laid by the 1st foundress that was a sibling,but decreased with the number of eggs laid by the 1st foundress that was a non-sibling.(2)The number of eggs laid bythe 1st foundress and the relationship between the two foundresses did not significantly influence the larvacideof the 2nd foundress.(3)The number of all eggs on a T.molitor pupa influenced the number of larvae matured and adults emerged,but did not affect sex ratios(male proportion).The results of this study suggestthat S.guani foundresses can recognize the relationship of offspring eggs by and adjusted oviposition decisions accordingly.2.Oviposition decisions of Sclerodermus guani in response to conspecifics on the host-mating manipulation experimentTo explore S.guani oviposition decisions on cooperatively parasitization,we grouped an unmated(A,producing only males)with a mated(B,producing ca.5%males)foundresses into six treatments:B,AB,ABB,ABBB,AAB,and AAAB.T.molitor and Saperda populnea were used as hosts,respectively.(1)The number of total eggs on a host increased with parasitoid-to-host ratio from 1:1 to 4:1,,but decreased per wasp.(2)More eggs were laid,but less survived to adulthood on T.molitor than on S.populnea.(3)Sex ratio of offspring(male proportion)decreased with increasing proportion of mated foundresses.(4)Males per brood increased with a brood size.The results of this study suggest that S.guani foundress can adjust oviposition decisions on the number of eggs and sex ratio according to the number of conspecifics on a host.3.Oviposition decisions of Sclerodermus guani in response to other foundresses on the host-sterilization experimentThe Co60 irradiation technique(40 Gy,2 Gy/min)was used to obtain infertile female wasps(H),which were grouped with healthy female wasps(N)in following ratios on a host:N,HN,HHN,HHHN,and NN,respectively.Number of eggs and sex ratio(proportion males)of emerged adults were observed.Irradiated foundresses laid eggs normally,but the eggs were consumed by foundresses.Thus all eggs lefted on the host were laid by the healthy foundresses that were together with irradiated foundresses.(1)Compared to the control(single healthy wasp),the healthy foundresses together with irradiated ones laid more eggs with increasing proportion of irradiated founresses.For example,the healthy foundress with 3 irradiated ones laid 41 eggs,but only 36 eggs per wasp on average by themselves.(2)Sex ratio of "NN" treatment was significantly higher than "N".(3)Sex ratio increased with irradiated foundresses.For instance,the sex ratio was 4.97%when one irradiated foundress was present,but increased to 11.75%when three irradiated foundresses were present.The results of this study suggest that S.guani may adjust oviposition decisions in response to the presence of conspecifics allocating greater clutch size and sex ratio when more conspecifics were present.