Relationship between structure and stability of a Halipegus occidualis component population in green frogs: A test of selective treatment

The aggregated nature of helminth parasite populations has led to the sugge stion that selectively treating heavily infected hosts can efficiently redu ce parasite abundance and morbidity within a host population. Moreover, it has been postulated that a selective treatment protocol might have long-ter m effects on parasite transmission by disrupting the stability attributed t o aggregated parasite population distributions by theoretical models. Long- term investigation has demonstrated year-to-year consistency in the populat ion dynamics of Halipeguys occidualis in green frogs from Charlie's Pond, N orth Carolina. In 1996, removal of all but 1 worm from each frog with great er than or equal to 15 worms reduced the estimated component worm populatio n by 45%, thereby decreasing mean intensity and aggregation (variance-to-me an ratio) of H. occidualis in the frogs by 85% and 63%, respectively. The f ollowing year, mean intensity, aggregation, and host colonization trends re turned to pretreatment levels, indicating no effect of worm removal and dem onstrating the stability of this host-parasite system. Although this result might be attributable to inefficient treatment or the presence of infectio n reservoirs, it is suggested that parasite population stability in this sy stem might be governed by prevalence rather than intensity of adult worms. Therefore, repeated selective treatment might effectively modify intensity- dependent morbidity in similar host-parasite systems but should not affect further parasite transmission.