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) parasitism on a host population of Panamanian howler monkeys (Alouatta palliata), 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 of howler monkey troops; and (v) analysis of blood samples from infected and uninfected monkeys. A complete life cycle of A. baeri takes approximately 13 weeks; larvae remain in howlers for approximately six weeks, 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 class, juveniles had a significantly higher prevalence and a significantly lower mean intensity than adults; the adult and juvenile classes both showed a significantly higher prevalence and mean intensity than the infant class. Such differences may relate to characteristics of younger age classes rather than host selectivity on the part of the parasite. Although larvae were observed in the howler population throughout the year, relative density fluctuated from month to month, showing from one to three significant peaks per year. Larvae were most abundant during the mid-to-late rainy Season (Aug.-Nov.). Relative density was strongly correlated with howler mortality. Several hematological parameters including serum albumin levels and albumin/globulin ratio were significantly lower in individuals with heavy larval burdens. No endoparasites or diseases were found in blood samples. I conclude that the annual pattern of howler mortality results from a synergistic effect between the age, physical condition, and fat reserves of parasitized individuals, the size of the larval burden, and increasing dietary stress as the rainy season progresses. The lack of growth in this closed primate population over >20 years apparently results, in large part, from primary and secondary effects of bot fly parasitism.