Aggregation Behavior And Chemical Communication Of Sclerodermus Guani

Sclerodermus guani Xiao et Wu（Hymenoptera:Bethylidae）has been widely used in biological control of forest caries in China.Due to its extensive host life,short life cycle,rapid reproduction,strong ecological adaptability and host searching ability,etc.As a typical subsocial insect,S.guani has the phenomenon of parental aggregated to cooperation in rearing offspring,so as to maximize the co-use of host resources and promote population reproduction.However,there are few reports on the aggregation behavior of S.guani.In this paper,the research object is S.guani and Monochamus alternatus.Our aim was to evaluate the aggregation behavior process and rules of parental and progeny of S.guani and the effects of parasite density on the parasitism and reproduction.From the perspective of insect behavioral biology and chemical ecology,we explored the potential chemical information substances that regulate the"parental-offspring"aggregation behavior of S.guani,providing important theoretical basis for the subsocial behavioral adaptation strategy and ecological significance of Bethylidae.1.Observation of aggregation behavior of Sclerodermus guaniIn order to clarify the characteristics and rules of the aggregation behavior of S.guani,the methods of indoor rearing and continuous video camera were used to observe the aggregation behavior of“parental-offspring”.The results showed that the male after eclosion mainly performed the mating task,but did not have the aggregation behavior,and died after mating with the female.（1）The aggregation of parental female adult wasps was mainly characterized by post-emergence aggregation and aggregated parasitism.Parental female adult began to gather in the eclosion nest after eclosion and spread after 3～5 days.In the early stage of dispersal,most of the female landed on the host with a density of 1 to 8（42.902±5.795%）,and 3 to 4 wasps were mainly parasitic.The parental female adults cooperated to overcome the host and concentrated their eggs on the back and sides of the same host.（2）The aggregation of offspring is mainly manifested as that the early-instar larva,late-instar larva and the prophase mature larva gather on the surface of the host for food,and when the offspring develop to the late mature larva stage,the parents will move the mature larvae away from the host debris and make them gathered spin,cocoon and pupate（after-removing mature larvae,Spinning mature larva and pupa cocoon）.By observing the distribution and displacement of mature larvae with or without parental transport,it was found that the probability of separation of mature larvae with parental transport was higher（61.250±6.700%）than that without parental transport,and the average displacement was less（7.040±0.449 mm）,and the offspring was aggregated.2.Effects of parasite density on the parasitism and reproduction efficiency of Sclerodermus guani（Hymenoptera:Bethylidae）Taking Monochamus alternatus larvae（0.350～0.450 g）as hosts,the parasitic behavior,parasitism efficiency and fecundity of female Sclerodermus guani,as well as the changes of offspring performance,were analyzed at different parasite density（1 to 8 parasites per host）.With the increase of foundress’s parasite density,the durations before first stinging,host paralysis and pre-oviposition of S.guani were shortened.As analytical model Hassell-Varley:E=0.9023×P^-0.9378showed,the foundress’s searching efficiency reduced with the increase of parasite density,and the interference among females lessened parasitism efficiency.Additionally the fecundity of foundress decreased with the increase of parasitism density,as the oviposition per female and number of female offspring significantly declined.At density of 1 female per host,the number of eggs was 1.4 and 2.4 times of 4 and 8 females per host.Besides,the offspring performance changed with the increase of parasitoid density,both the duration of offspring development,the survival rate of early instar larvae and the weight of single offspring female significantly reduced respectively.At density of 1 female per host,the duration of offspring development was averagely 26.7 d,being the longest.While the shortest duration was 24.0 d at 8 female per host.The survival rate of larvae and the weight of single offspring female were 1.1and 2.1 times of that at 8 female per host.Among offspring,the male proportion were less than 15%throught all experimental treatments and showed a slight downward trend with the increase of foundress’s parasite density.Overall,multiple parasitoid can improve the parasitism efficiency,shorten the development duration of offspring,increase the number of offspring,and achieve the maximum reproductive benefit when the density of parasitoid is 4 females per host.3.Potential chemical informators that regulate the aggregation behavior of S.guaniAccording to analysis the qualitative and quantitative of the chemical information substances in the different stage that may regulate the aggregation behavior of S.guani.A total of 30 compounds were identified,including n-alkanes,alcohols,esters,acids and aldehydes.GC-MS results showed that the components and contents of different odor sources were different.Camphene and 3-carene were only found on the surface of fresh hosts,which were 0.026 ng/mg and 1.273 ng/mg,respectively,indicating that 13.461 ng camphene and 655.927 ng3-carene could be released from each fresh host.Bioassay showed that female adult wasps reacted significantly to host remains,eclosion environment complex,fresh host and mature larva extracts,and the concentration of pentacosane was the highest in the four extracts.It was speculated that pentacosane might cause the aggregation of female adult wasps.In addition,camphene and 3-carene,unique terpenes from the host surface,may attract female to gather during the host searching stage.The abundance of 1-docodiene,n-24 alcohol and1-Heptacosanol in the eclosion environment complex of female may also be closely related to the aggregation behavior of female during eclosion.