ECOLOGY OF HUNTERELLUS-HOOKERI (HYMENOPTERA, ENCYRTIDAE) AND EVALUATION OF ITS IMPACT ON IXODES-SCAPULARIS (ACARI, IXODIDAE) ON NONAMESSET ISLAND IN MASSACHUSETTS

The impact of Hunterellus hookeri Howard on Ixodes scapularis Say was examined in 1990-1992 at a site in coastal Massachusetts where the par asitoid was released in 1926. Rates of nymphal parasitism were estimat ed from regression as 25, 21, and 26% for the 3 yr of observation. Ana lysis of the rates of decline in percentage parasitism values from sam ples of held-collected nymphs that were dissected immediately compared vith subsamples held in the laboratory for 0-4 mo suggests that paras itized nymphs experience enhanced mortality (before parasitoid emergen ce) compared with unparasitized nymphs. Voltinism and host preferences of H. hookeri also were examined. Analysis of developmental times and seasonality of hosts suggests that >1 generation per year of H. hooke ri is unlikely in southeastern Massachusetts. Significantly more I, sc apularis nymphs than larvae became parasitized when these stages were exposed together to H. hookeri while feeding on a laboratory mouse. H. hookeri also parasitized 9% of fed, detached I. scapular-is larvae th at were exposed in a petri dish. Parasitism rates of fed I. scapularis lan ae collected from Peromyscus leucopus (Rafinesque) in the field a nd larvae exposed to H. hookeri while feeding on P. leucopus in a labo ratory arena were low (1% and 6%, respectively). These rates are too l ow to account for the level of parasitism seen in the field ill unfed, questing nymphs (21-26%). This Ending implies that while some parasit ism may occur on mice under field conditions, larger mammals or detach ed larval ticks must be the principal site where H. hookeri encounters and oviposits in ticks. Further field studies of parasitism of larval ticks on larger mammals would be needed to clarify this issue.