Mechanisms of evolution of sterile defensive cast in aphids.

在鹿儿岛县的竹丛林中，对具有不育防御性种姓（兵）的竹假网蝽（Pseudoregma bambucicola）和竹假网蝽（P.koshunensis）的社会生物学进行了研究，在名古屋大学的饲养室里。结果表明：（1）竹子全爪螨群体中的幼虫比例在秋季随着寄主新茎的生长而增加，复相关分析表明，影响幼虫比例增加的主要因素是群体大小和竹茎长度，这与群体发育的时间有关。2)释放试验和田间观察表明，竹栖拟青霉士兵能有效地杀死捕食性蚜虫Eupeodes confrator的1龄幼虫。成年雌虫E.这可能是由于在受扰时，剑形虫会主动摇动腿，从而避免在剑形虫比例高的蚜虫群体附近产卵。3)无翅胎生幼仔先产下正常幼仔，再产下兵丁，到了生命的最后阶段，再产下正常幼仔。首先产下正常的生殖种姓，其次产下不育种姓，这与所有其他真社会性昆虫产下这些种姓的顺序正好相反。这一发现为进一步研究昆虫防御性等级的进化提供了线索。

Social biology of Pseudoregma bambucicola and P. koshunensis, both of which have sterile defensive caste (soldier), was studied in Bambusa multiples stands in Kagoshima Pref., and in a rearing room of Nagoya University. The results obtained are as follows: 1) Ratio of soldiers in P. bambucicola colonies became increase in Autumn, when new stems of the host grew, and multiple correlation analysis showed that major factor concerning increase of soldier ratio were colony size and length of bamboo stems, which related to period of colony development. 2) Release experiments and field observations suggested that P. bambucicola soldiers could effectively kill first instar larvae of a predatory syrphid, Eupeodes confrator. Adult females of E. confrator avoided to oviposit near aphid colonies with high soldier ratio, possibly due to active shaking of legs by soldiers when disturbed. 3) Apterous viviparae of P. koshunensis laid some normal larvae first, some soldiers secondly, and in the final stage of their life, laid normal larvae again. Laying normal reproductive caste first and sterile caste secondly is the very reverse of order of laying these castes in all other eusocial insects. It was considered that this discovery may shed a light for further consideration of evolution of defensive castes in insects.