Life-cycle variation in the aphid Sitobion avenae:: costs and benefits of male production

1. Patterns of male production and life-cycle variation were investigated in the aphid Sitobion avenae. Seventy-seven field-collected clones were subjected to a 14degreesC short day-length regime to assess their reproductive modes, and three clones were used to study life-cycle inheritance. A further analysis assessed the cost of male production. 2. In comparison with those from East Anglia, there were more holocyclic and intermediate clones found in Scottish populations, and they produced significantly more mating females. In total, 44% of clones were androcyclic. 3. The inheritance of life cycle showed a greater level of complexity than could be achieved by previously suggested monohybrid inheritance mechanisms. 4. Holocyclic and intermediate clones produced a higher proportion of males than did androcyclic clones. Inter-clonal differences were reflected in the pattern of male production in the reproductive sequence. 5. A significant cost was associated with male production in terms of a reduction in both fecundity and total offspring biomass. 6. Winged females rarely gave birth to males but the pattern of mating female production differed between holocyclic and intermediate clones. 7. Patterns of male and mating female production by the different types of clone may be related to different advantages and disadvantages of dispersal and inbreeding. 8. Recent models of aphid overwintering could be enhanced by consideration of issues raised in this study, such as the cost of male production, the inheritance of life cycle, and the patterns of sexual morph production.