Epizootiology of the reindeer nose bot fly,Cephenemyia trompe(Modeer) (Diptera: Oestridae), in reindeer,Rangifer tarandus(L.), in Norway

Abstract

First-instar larvae of the reindeer nose bot fly, Cephenemyia trompe (Modeer) (Diptera: Oestridae), were sampled with a rinsing and sieving technique from 571 semidomesticated reindeer, Rangifer tarandus (L.), from different districts in northern Norway in the infection years 1983, 1984, 1985, 1987, and 1988, and from 44 wild reindeer from southern Norway (infection year 1983). This is the first comprehensive epizootiological study of this parasite from Fennoscandia. The first instar was found between 10 September to 25 May, the second instar from 11 February to 17 May, and the third instar from 3 April to 28 June. Old third-instar larvae were sometimes found trapped in the sinuses of the host. The overall prevalence of infection was 65.2% (range 6.7 – 100%) and the abundance (= relative density) was 11.53 (range 6.7 – 62.7). Individual intensities ranged from 0 to 221. There were significant differences in abundance between some districts and years. Distance and timing of the spring migration of the host are thought to be the major factors causing variability in infection levels between districts, whereas the summer climate during infection greatly influenced the differences between years. The frequency distribution was highly overdispersed (aggregated) and could adequately be described by the negative binomial model (overall parameter, k = 0.29, range 0.03 – 2.64). Heterogeneity in host behaviour during infestation is hypothesized to create this parasite distribution. Two measures of aggregation, Morisita's index of aggregation (IM) and1/k, decreased with larval burden, indicating that factors restricting parasite numbers (negative feedback) start to operate at high infection levels.