Study on sexal-selection and mating success of a subsocial spider mite.

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1999 : I conducted behavioral and morphological observations on Schizotetranychus miscanthi Saito which has subsocial life. I first established several morphological characters of S.miscanthi which reflect mite body size regardless of mounting methods. Then I conducted field surveys on male distribution patters over nests in order to know how the male-male aggressions observed under experimental conditions really reflect male behavior in fields. The result showed that the male-male aggression in S.miscanthi well correspond to the male aggregation pattern per nest in fields. Furthermore, it was revealed that the two groups of S.miscanthi having different levels of male aggression are sexually isolated and they are considered to be different sub-species or species.2000 : The potential males (just before molting) and actual males (adult) of S.miscanthi were collected in various districts and inspected their morphology. The male leg I length of Iriomote population showed bimodal frequency distribution, though it showed uni-modal distribution in most populations of Honshu and Kyushu Islands, seggesting division of male mating tactic in Iriomote population. Under experimental conditions, I could get small and large adults by controlling food conditions. Then the mating success of males and females having different body size was evaluated. The result showed that there is no significant difference among all combinations during 24 hr mating period. However, in order to know more precise result, I should continue this experiment by shortening the mating period in the future.