Clonal mixing in bamboo stem aphid Pseudoregma bambucicola (Hemiptera: Hormaphidinae)

About 50 species of aphids producing soldiers to increase the fitness of their colony are known as social insects. These aphids hold a special place in social insects because of their parthenogenetic reproduction. Therefore, the members of a colony are genetically identical, which means soldiers should have the same genome type with their colony mates. The bamboo stem aphid, Pseudoregma bambucicola, is a kind of gall-forming social aphids, and their soldiers play a role as defenders to guard on the entrance of galls. Several studies have reported aphids invading galls of conspecies. The fitness of the host clone may reduce if the invasion of conspecific aphids succeeds, and clonal mixing phenomena in galls may be observed. Using field trapping and genetic markers, clonal mixing in the field populations was detected. From the result of field observation, the migration of aphids was mostly found from July to September. In addition, limited space of galls might cause intergall migrations. Two genetic makers, mitochondrial COI gene and inter-simple sequence repeat (ISSR), were used to detect clonal mixing. No difference was found in mitochondria COI gene among different colonies. On the other hand, ISSR expressed specific fragments between colonies, and used in clonal mixing analysis. From the trapping, most members of migrants were identical as non-soldiers. By genetic analysis, soldiers were the main member who caused clonal mixing. This inconsistency between field trapping and genetic results might be explained by the defense efficiency and caste recognition of soldiers. Soldiers of P. bambucicola are sterile; they join to non-kin clones can’t cause menace. On the other hand, non-soldiers have the potential to decrease the quality and quantity of food recourses. By these reasons, guarding soldiers prevent invasions of non-soldiers to decrease the food competition between kin and non-kin, but accept that of soldiers to increase the defensive efficiency of their colonies. This study provided a good evidence on the defensive efficiency and caste recognition of soldiers to prevent their clones from clonal mixing to some extents.