| Sclerodermus(Hymenoptera:Bethylidae)is a group of quasi-social parasitoids which females tending each other’s offspring on shared host.They has been widely used in biological control of wood-boring insects in China,owing to their high reproductive potantal,strong search ability and wide host ranges.Previous studies of this parasitoids mainly focused on bionomics,mass-production and release techniques for biological control applications.Less attention has been put on behavioral ecology.This thesis study,using S.guani and Tenebrio molitor as a parasitoid-host system,focused on three questions:① Do foundresses exercise guarding behaviour to protect their hosts in response to an intruder parasitoid?② Which factors influence the host-guarding behaviour?③Does the host-guarding behaviour affect brood-tending consequences?The answer to these questions would increase our understanding of Sclerodermus social behavior.In what follows are main results and conclusions obtained from this study.1.Host-guarding behaviours(1)Host-guarding behaviours.To clarify whether foundresses perform guarding behaviour to protect their host,two foundresses were introduced in succession to a host;the first was referred to as an occupant and the later intruder.Six stages across the process of paraitizing a particular host were operated for their encounter as treatment levels:cleaning,feeding,preparation,egg-laying,young larva,and mature larva stages.Behaviors of the ocupant in response to arrival of an intruder were recorded as four categories ① accepting,which came up with host sharing with the intruder,referred to as "non-aggressive guarding behavior";②surrounding the host while rubbing the abdomen with metalegs,referred to as "threatening”;③ leaving the host and driving away the intruder,"driving-away";④stinging with ovipositior or biting with mandibles the intruder,"attacking";the later three types of behaviors were categorized as "aggressive guarding behaviors".The four behavioral responses increased in intensity from the accepting to attacking and were thus treated as an order variavble.The proportional odds model was used to analyze the odds of host-guarding behavioural reposnes.The results showed host-guarding behaviours were affected by the stage treatment.Compared to the cleaning stage,the odds of exercising host-guarding behavior increased at the stage of egg-laying by 5.18 times,young larva by 2.35 times and mature larva by 3,52 times.The results from this study suggest that foundresses are active in guarding their hosts after starting oviposition.(2)Factors affecting host-quarding behavior.Following factors were applied in a factorial design to examine host-guarding behaviors of occupant foundresses:number of occupants(four levels:1,2,3,or 4),stage(two levels:pre-oviposition,opst-ovipistion),and kinship(two levels:occupant and intruder foundresses were sibling or not).The experiment showed following results.① The number of occupants and the stage interacted to have a significant effect on host-guarding behaviour.The likelihood of exercising guarding behavior by a single occupant was higer than that by more occupants.② Host-guarding behaviour did not differ between sibling and non-sibling foundresses.The results suggest that foundresses depend on each other to make the decision on host-guarding behavior.2.Effects of host-guarding behaviours on brood-tending consequences by a single occupant(1)Effects of encountering stage.Encountering stage was manipulated as six stages across the process of paraitizing a particular host:cleaning,feeding,preparation,egg-laying,young larva,and mature larva stages.Guarding behavior was exercised or not;the control was devoid of an intruder.These two factors were crossed in a factorial way.① The stage and guarding behavior interacted to have a effect on the number of emerged offspring.At the feeding or egg-laying stage,the occupant exercising guarding behavior increased offspring number compared to that no-exercising it.②The occupant encountering an intruder at the feeding stage had large-body offspring.③ Sex ratio was not influenced.The results suggest that occupant foundresses can alter brood size yet not sex ratio as a consequence of encountering an intruder.(2)Effects of the number of occupants.Following factors were examined:the number of occupants was 1,2,3,or 4;the encountering stage was pre-oviposition or post-oviposition;behavioral response of the occupant was aggressive or not;the control was devoide of intruders.These factors were crossed in a factorial way.①The number of occupants by the encountering stage interaction had an effect on the number of emerged offspring.Compared to the pre-oviposition stage,the number of occupants encountering the intruder at post-oviposition stage had an increading effect on the number of offspring parasitoids emerged.② Body size of offspring parasitoids under the 4 occupants was significantly smaller than the 2 or 3 ones.③ Offspring sex ratio was influenced by interactions between the number of occupants and the sencountering tage,and between the number of occupants and guarding behavior.Sex ratio(male proportion)reached as high as 12%if the 2 occupants did not exercise agreesive guarding behavior when encountering an intruder at the post-ovipostion stage.It achieved as low as 6%if 1 occupant exercised aggressive guarding behavior when encountering an intruder at the pre-oviposition stage.Sex ratio was not influenced by the number of occupants if the occupant did not exercise aggressive guarding behavior when encountering an intruder at the ovipostion stage,but it achieved as high as 13%if 4 occupants exercised aggressive guarding behavior.The results from this study suggest that the number of occupants in interaction with encountering stage and guarding behavior can affect offspring sex ratio and body size.3.Effects of guarding behaviour on brood tending consequences by two occupantsFollowing factors were examined:the encountering stage(pre-oviposition,post-oviposition);kinship(sibling,non-sibling);and behavioral response(aggressive or not,with the control where two occupants simultaneously on the host).The results did not show these factors affecting offspring number,body size and sex ratio.It is interesting to note that the two foundresses were not symetric in offspring production.When the enountering stage was the oviposition,the occupant took a major share while the intruder took a minor or even none of females in offspring adults emerged.The results suggest that occupant and intruder foundresses may not symmetric in sharing the brood they tend.In summary,this research indicates that S.guani exercises host-guarding behavior in response to intruding female parasitoids and this response can vary with the number of occupants on the host and the stage enoucntering intruders.Host-guarding behaviors affect the consequences of brood tending by either the occupant alone or together.Occupant and intruder foundresses may be not symmetric in sharing the brood they attend;the occupant takes a major share when encountering the intruder at the stage of post-ovipsition. |
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