The effects of oviposition aggregation on the incidence of sheep blowfly strike

The distribution of a parasite population within its natural host populatio n can have a significant influence on the dynamics of both the host and par asite populations. The majority of parasite species are typically distribut ed in an aggregated manner within the host population, leaving most hosts l ightly infected and a few hosts supporting very large parasite burdens. Thi s paper presents a consideration of the effects of aggregation on the incid ence of ovine cutaneous myiasis caused by the sheep blowfly, Lucilia serica ta (Meigen). Using simulation analysis, the mechanisms causing larval aggre gation are included in the model, allowing the consequences for control to be investigated. By explicitly incorporating host susceptibility, it become s apparent that early in the season, strategies targeting the blowfly popul ation may prove more effective in suppressing strike levels, whereas later in the season, treatment of the sheep population may be more beneficial. Th e analysis also shows that the greater the degree of aggregation, the fewer sheep that become struck and, hence, suggests that increasing the heteroge neity in susceptibility amongst a flock of sheep restricts strikes to relat ively few sheep. Providing the highly-susceptible sheep could be identified , concentrating strikes on a low number of sheep would allow fewer sheep to be treated, leading to a more efficient means of controlling the blowfly p opulation and suppressing strike. (C) 1999 Elsevier Science B.V. All rights reserved.