EFFECTS OF BOT FLY (ALOUATTAMYIA-BAERI) PARASITISM ON A FREE-RANGING HOWLER MONKEY (ALOUATTA-PALLIATA) POPULATION IN PANAMA

To evaluate effects of persistent bot fly (Alouattamyia baeri) parasit ism on a host population of Panamanian howler monkeys (Alouatta pallia ta), a 68-month study was carried out which included: (i) examination of the parasite's life cycle; (ii) monthly estimates of prevalence and mean intensity; (iii) monitoring of howler mortality; (iv) censuses o f howler monkey troops; and (v) analysis of blood samples from infecte d and uninfected monkeys. A complete life cycle of A. baeri takes appr oximately 13 weeks; larvae remain in howlers for approximately six wee ks, passing through three instars. Overall prevalence of infection was 60%, overall mean intensity 2.8 +/- 0.04. No difference in prevalence or mean intensity was found between adult males and Females. As a cla ss, juveniles had a significantly higher prevalence and a significantl y lower mean intensity than adults; the adult and juvenile classes bot h showed a significantly higher prevalence and mean intensity than the infant class. Such differences may relate to characteristics of young er age classes rather than host selectivity on the part of the parasit e. Although larvae were observed in the howler population throughout t he year, relative density fluctuated from month to month, showing from one to three significant peaks per year. Larvae were most abundant du ring the mid-to-late rainy Season (Aug.-Nov.). Relative density was st rongly correlated with howler mortality. Several hematological paramet ers including serum albumin levels and albumin/globulin ratio were sig nificantly lower in individuals with heavy larval burdens. No endopara sites or diseases were found in blood samples. I conclude that the ann ual pattern of howler mortality results from a synergistic effect betw een the age, physical condition, and fat reserves of parasitized indiv iduals, the size of the larval burden, and increasing dietary stress a s the rainy season progresses. The lack of growth in this closed prima te population over >20 years apparently results, in large part, from p rimary and secondary effects of bot fly parasitism.