A fitness cost of eugregarine parasitism in a damselfly

1. Adult Calopteryx splendens xanthostoma are infected by the trophozoites of a eugregarine parasite that attaches to the mid-gut epithelium. 2. The results of this study show: (1) that eugregarines were the predomina nt parasite in the isolated study population, (2) they were not present in images that had just eclosed from larvae but were present in significantly higher numbers in older adults, (3) animals with a eugregarine burden durin g the prereproductive fat-accumulation period of their adult development (t he teneral stage) had significantly lower fat content, and (4) males infect ed artificially with eugregarine oocysts showed no correlation between eugr egarine burdens and postmanipulation fat content. 3. Infection with eugregarine trophozoites during the teneral life-history stage affects the ability of damselflies to accumulate fat, and consequentl y reduces their ability to fight for, and maintain, a territory when they b ecome reproductively active.