The population of the louse‐fly, Crataerina pallida (Diptera, Hippoboscidae) on the European swift, Apus apus (Aves, Apodidae)

Abstract

Data are presented on the seasonal changes in the population of the louse‐fly Crataerina pallida, parasitic on swifts, Apus apus, from the examination of 4094 birds. The swifts arrive to breed in Britain free from this parasite, but the flies soon emerge from pupae in the hosts’nests. The population of adult flies builds up rapidly towards the time when the young birds start to hatch. At this stage up to 70% of the birds trapped were infested. By the time the main hatch of young birds occurs the population on the full grown birds is declining, and continues to decline until flies are absent by the time the birds migrate. Male flies emerge first, and as the season progresses the proportion of males declines and males disappear first. Heavy infestations were frequent with up to 31 flies per bird, but there seemed no relationship between these heavy infestations and poor condition of host (in weight, plumage, etc.). Seven juvenile birds were trapped, but were not heavily infested. Only one fly was found on the 37 first‐year birds examined.

Sources of Variability in Aggregation and Sex Ratios of Crataerina melbae (Diptera: Hippoboscidae) among Adult Colonial Alpine Swifts

“…Parasitic species typically exhibit aggregated population distributions. This is the case for C. pallida (Hutson 1981) and for C. melba (Tella & Jovani 2000), although the level of aggregation seen by these species is lower than seen in other host-parasite systems.…”

“…No pathogenic effect of C. pallida parasitism on their A. apus hosts has been found (Lee and Clayton 1995;Tompkins et al 1996;Hutson 1981). This is surprising.…”

“…Pupae are cyclorrhaphous. Although emergence has been found to coincide with the hatching of swift nestlings (Bütiker 1944;Lack 1956), others have found that it occurred earlier (Hutson 1981;Bromhall 1980). In 2007, the first C. pallida emerged on 15 May, during the period of swift egg laying (e.g.…”

“…On adult alpine swifts infestation rates by C. melba of 70.8% (Tella and Jovani 2000) and of 74% (Tella et al 1995) averaged over the summer were found. On A. apus adults parasitized by C. pallida the average infestation over the entire season was 34.4% (Hutson 1981), and at A. apus nests 67% (Tompkins et al 1996). For comparison, the prevalence of the louse fly Ornithomyia avicularia, on serins S. serinus, was found to be 3% (Senar et al 1994), and the prevalence of other Hippoboscid flies on other species has been shown to be no greater than 20% (McClure 1984).…”

“…More female than male C. hirundinus were found at house martin nests and on adults (Summers 1975;Popov 1965;Hardenberg 1929); likewise for C. melba at alpine swift nests (Tella and Jovani 2000). A greater proportion of female than male C. pallida has been seen on adult A. apus (Hutson 1981). This female bias is puzzling as an equal number of males and females are thought to hatch (Bequaert 1953).…”