| The bethylid wasp Sclerodermus guani Xiao et Wu(Hymenoptera:Bethylidae),an ectoparasitoid,is widely used in augmentative biological control of wood-boring insect pests in forests in PR China.The wasp is unique to parasitoids in cooperatively tending brood on a host among foundresses.Numerous studies of the parasitoid have been made,mainly focusing on bionomics for biological control,including development,host range,parasitism,and fecundity.However,few studies have been made on the wasp's cooperative maternal care and sex ratios for the theoretical understanding of quasi-social behavior.In this thesis,I firstly focused on aggregation behavior of S.guani,ecological functions of cooperative host exploitation,and the influence of foundress genetic relationship on cooperative brood-tending.I then focused on effects of maternal care on offspring developmental performances.I finally focused on the sex ratios.The results of this thesis study obtain increased understanding of insect social behavior evolution in general,and parasitoid social behavioral ecology in particular.Main results and conclusions obtained are summarized below.1.Adaptation of cooperative brood-tending(1)Aggregation behavior of S.guani.A dual choice trail was set up,including two host larvae,with and without foundresses on it,to a female parasitoid.The results indicated that the female show the preference for hosts with foundresses without regarding to the number of foundress on the host.The results reveals that the social behavior in S.guani.(2)Adaptions of cooperative host exploitation in S.guani.To examine mutually beneficial host exploitation in S.guani,Numbers of S.guani foundresses as 1,2,4,6,and 8,respectively,were exposed to a host larva(Monochamus alternatus),which varied continuously in body weight within a wide range.Offspring developmental time,clutch size(number of eggs laid on host),offspring reproductive success,offspring production and offspring body size were investigated.The results showed:?the time to oviposition significantly increased with host body weight but decreased as foundress number increased;?host body weight and foundress number had no significant influence on egg,larval and pupal development time,which were 7.27,6.81,and 14.38 d on average,respectively;?Host body weight and foundress number affected significantly the eggs laid on the host,the amount of eggs laid increased as host body weight and foundress number increased,separately;?The mean number of eggs laid per foundress increased significantly with host body weight but decreased as foundress number increased;?The probability of producing adult offspring successfully was affected significantly by host body weight and foundress number,increasing with foundress number,but decreasing as host body weight increased;?The results also indicated that for the largest hosts(>0.33g),the average offspring per foundress(females benefited most)was highest when the females in groups of eight foundresses;?Female offspring size was not correlated with host body weight and foundress number,but increased weakly with host body weight.This study indicated that mutually beneficial host suppression in S.guani and first found "Allee effect" in parasitoid wasps.(3)The influence of foundress genetic relationship on cooperative care behavior in S.guani.To examine genetic relationship between cooperation females may affect offspring development related fitness.We compared sibling and non-sibling foundresses in cooperative care of offspring development fitness.The results indicated that the kin relationship between foundresses had no significant influence on egg survival rate,pupation rate,offspring sex ratio and female body weight,but offspring emergence rate was a little higher when the brood tended by sibling foundresses than when it was supplied by non-sibling foundreeses.The results suggested that offspring development fitness was not significantly higher when offspring tended by close related foundresses,and because female cooperation directly increase per-female benefits,females cooperation may occur among unrelated individuals.2.Effects of mother-offspring kin relationship and tending duration on offspring fitness-related developmental performancesTo assess the effect of mother-offspring relationship and female tending duration on offspring development,I analyzed the difference of care behavior on offspring ?between nature mother and stepmother which had laid eggs before.The results showed eggs survival rate was significantly higher when tended by natural mother than that tended by stepmother,the eggs survival rate was 90.67%and 85.39%,separately;Offspring-mother genetic relationship had significantly effect on offspring emergence rate,which was 95.5%when tended by natural mother and 91.44%when tended by stepmother.Offspring sex ratio and female body size was not correlated with mother-offspring genetic relationship.And then the tending duration time was divided into three parts artificially according to the offspring development time:tend lasted to egg stage finished,lasted to larva stage finished and lasted to the offspring emergence.Analyze how the different type tending mother under three different tending duration affected the offspring development fitness.The results indicated that egg survival rate was affected significantly by tending duration,increasing as tending duration increased.Tending duration had no significant influence on pupation rate,but the pupation rate was significantly lower when offspring tended by stepmother.Naked pupae emergence rate decreased significantly as tending duration time increased.Tending duration did not affected offspring emergence rate,but tending females' type had a significant influence on offspring emergence rate.Especially,offspring emergence rate was significantly high when offspring were tended together by natural and stepmother.Tending duration and tending females' type did not affect offspring sex ratio and female body size,but female offspring average weight was high weakly when mothers tended the offspring till emergence.The results suggested that mother-offspring genetic relationship and tending duration affected offspring fitness-related developmental performances.3.Adaptation of sex allocationTo test whether the sex ratios in S.guani can be explained by the Local Mate Competition(LMC)theory,a series of experiments was conducted to address the following question:(1)how does host body weight and foundress number affect sex ratios?(2)how were the sex ratios related to foundress number and clutch size?and(3)how the proportion of broods which contain only females at emergence(virgin broods)was affected by offspring developmental mortality and clutch size.The results showed that:(1)sex ratios in S.guani was contingent on an interaction between foundress number and host body weight.The proportion of males offspring rose obviously as host weight increased when foundress number was only one.When foundress number was 2 or 4,the proportion of males offspring rose weakly as host ?body weight increased.But when foundress number was 6 or 8,the proportion of males offspring declined as host body weight increased.Sex ratios in S.guani increased as the number of foundresses increased but for multiple foundress cases sex ratios were far more biased than would be predicted by classical LMC theory.(2)Sex ratios declined weakly with adult offspring group size and rose weakly with foundress number.Offspring developmental significantly affected the proportion of males offspring in offspring group.Sex ratios were significantly higher among broods that had experienced higher proportions of developmental mortality.(3)About 15.3%of adult offspring groups consisted of female offspring only.The probability of an offspring group consisting only of females significantly decreased with offspring group size,no broods of more than around 50 maturing offspring contained females only.The probability of all-female offspring groups increased significantly with offspring developmental mortality and decreased significantly with the number of foundress number on host.This study suggested that sex ratios in S.guani can be explained by the Local Resource Enhancement theory. |
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