| Sclerodermus guani Xiao et Wu(Hymenoptera:Bethylidae)is an ectoparasitoid,and widely used in biological control of wood-boring forest pests,mainly long horned beetles.Sclerodermus parasitoids are unique among parasitic hymenopteran wasps by foundresses tending each other’s offspring.The understanding of the adaptation of such quasi-social behavior is rudimentary.The working hypothesis of this thesis study is that foundresses that have colonized a host should contest with intruder female parasitoids over the host.To test the hypothesis,we first examined the effect of body size of foundresses(mated females)on maternal care of offspring,and then focused on contesting behaviors between colonizer and intruder foundresses as affected by relevant biological factors.The main results and conclusions are summarized as follows1.Effects of S.guani foundress body size on oviposition and brood tending outcomeTo explore the effect of body size of S.guani foundresses on the fecundity and offspring performances,foundresses were divided by body size into small and large body groups.Each foundress from either groups was provided with one Saperda populnea L.larva for parasitism.Traits were observed,including pro-oviposition time,foundresses life span,number of offspring eggs,mature larva,and emerged offspring,sex ratio and female offspring body size.(1)The pro-oviposition time of large foundresses(117.8 h)(the mean± standard error,the same below)was significantly shorter than that of small ones(160.7 h).(2)Life span of large foundresses was significantly longer than that of small ones.(3)Foundress body size did not significantly affect egg hatching rate and adult eclosion rate.(4)Foundress body size did not significantly affect Sex ratio of offspring and hind tibia length of female adults.The results of this study suggest that body size is positively correlated with fitness.2.Host-choice behaviors of S.guani femalesTo examine the preference of female parasitoids for different hosts,two bioassays were made in the microcosmoses to determine whether female parasitoids show preferences between healthy and parasitoized hosts,and whether female parasitoids together choose a host.The Y-shaped tube was used to make a dual-choice trial between a health host at one end and a parasitized host together with a foundress at the other end.The result showed that the health host was chosen by female wasps in 16 out of 30 trials,accounting for 53.33%.This result indicates that Sclerodermus guani females do not discriminate between health and parasitized hosts.Two sibling or non-sibling female wasps(3-day old)were introduced into a petri-dish where there were two S.populnea larvae.The wasps were continuously followed to note their colonization of the hosts.The result showed that sibling wasps together colonize a host by 57.14%in 30 trials and non-sibling ones by 42.86%;no significant differences were found between treatments.These results suggest that kinship between female parasitoids may do not influence their choice of hosts and the wasp may not be able to discriminate between healthy and parasitized hosts.3.Contest behaviors(1)Effects of kinship and colonization period on contest behaviors.Two foundresses were introduced in succession to a host,with the first referred to as colonizer wasp and the latter intruder wasp.Kinship between colonizer and intruder(sibling and non-sibling)and colonization period(abdominal enlargement and after oviposition)were manipulated as a factorial combination.Results showed that the proportion of contests between colonizer and intruder was not different between sibling and between non-sibling foundresses,but was six times during post-oviposition period(56.8%)more than that during pre-oviposition period(6.25%).The results suggest that contest behavior takes place more often when the colonizer oviposits than before ovipsoition,and kinship between foundresses may do not influence their contest behavior.(2)Influence of and number of colonizers and kinship on contest behavior.A factorial trial between the number(1 vs 2)of colonizers and kinhip(sibling vs non-sibling)between colonizer and intruder was performed.The trial showed a higher proportion(37.17%)of contests when one foundress colonized the host than when two did(6.26%).The proportion of contesting was similar between siblings(6.25%)and between non-siblings(6.07%).The results suggest that colonizing foundresses may depend on each other in defending their host.(3)Influence of relationship and colonization period on contesting behavior.Four treatments were imposed on colonizer and intruder foundresses by their relationship by birth and growth:non-sibling&developed on the same host,non-sibling&developed on different hosts,sibling&developed on the same host,sibling&developed on different hosts.The colonization period was manipulated as 1,3,5 and 7 days post oviposition.A 4-level scale(from 0,no contest,to 3,the strongest contest)was used to measure the encountering behavior between colonizer and intruder foundresses.To examine the effect of the contest on brood tending,offspring parasitoids were followed until adults emerged.The odds of contesting grades increased by 55%with each unit increase in post-oviposition time.The odds of contesting grades for the "sibling&developed on the same host" foundresses of(the closest relationsip)decreased by a factor of 1.40 compared to those under the other three treatments,but no significant differences occurred among the other treatments.The observation of offspring development of foundresses involved in contests showed that the number of emerging offspring adults decreased with host body weight for "non-sibling&developed on the same host" and "sibling&developed on different hosts" foundresses,but increased for the other foundresses.Female body weight of offspring was not affected by contesting and relationship between foundresses.The results suggest that the contest between foundresses varies depending strongly on the colonization period,but relationship between two wasps may play a minor role.(4)Influence of foundress body size and colonization period on contest behavior.Colonizer and intruder foundresses were paired by their relative body sizes as one small and another large.The interval in time between their encountering was set as 1,3,5 or 7 days post oviposition of colonizer foundresses.① With each unit increase in the interval time,the odds of contesting grades increased by almost 40%.The odds of contesting grades increased by 2.4 times for larger colonizers than smaller ones.② The number of emerging offspring parasitoids decreased for smaller colonizers compared to that for larger ones;it increased with host body weight,and was greater when the foundress had the experience of contesting than that did not.③ F1 female adult size was not influenced by the experience of contesting ④ Sex ratio of offspring was invariable with factors tested.The results of the study suggest that being larger in body size for colonizer foundresses has a clear advantage over being small in the contest. |
