Variation in the intensity and prevalence of macroparasites in migratory caribou: a quasi-circumpolar study

Comparative studies across time and geographical regions are useful to improve our understanding of the health of wildlife populations. Our goal was to study parasitism in migratory caribou (Rangifer tarandus (L., 1758)) of North America and Greenland. A total of 1507 caribou were sampled across 12 herds to assess seven of their main helminth and arthropod macroparasites between 1978 and 2010. We sought to determine which factors such as sex, age class, herd size, and season best explained the prevalence and intensity of those parasites. Intensity of warble fly (Hypoderma tarandi (L., 1758)) larvae increased with age for males, whereas the opposite was observed in females. Prevalence of giant liver flukes (Fascioloides magna (Bassi, 1875) Ward, 1917), tapeworm Taenia hydatigena Pallas, 1766, and nose bot fly (Cephenemyia trompe (Modeer, 1786)) larvae was higher in adults than in calves. Prevalence of F. magna and T. hydatigena was higher at high herd size than at lower herd size. Greenland herds had the lowest prevalence of T. hydatigena and of the tapeworm Taenia krabbei Moniez, 1879, a higher intensity of H. tarandi, and a higher prevalence of C. trompe than the other herds. Of the herds from Quebec and Labrador, the Rivière-George herd had a higher prevalence of F. magna than the Rivière-aux-Feuilles herd. Our research provides the first comparative survey of these parasites of caribou across a broad spatial–temporal range.

Failure of two consecutive annual treatments with ivermectin to eradicate the reindeer parasites (Hypoderma tarandi, Cephenemyia trompe and Linguatula arctica) from an island in northern Norway

The highly efficient endectocide ivermectin is used to reduce the burden of parasites in many semidomestic reindeer herds in northern Fennoscandia. In the autumn of 1995 and 1996 all reindeer on the island of Silda (42 km2) were treated with ivermectin in an attempt to eradicate the warble fly (Hypoderma (=Oedemagena) tarandi (L.)), the nose bot fly (Cephenemyia trompe (Modeer)) (Diptera: Oestridae) and the sinus worm (Linguatula arctica Riley, Haugerud and Nilssen) (Pentastomida: Linguatulidae). Silda is situated 2-3 km off the mainland of Finnmark, northern Norway, and supports about 475 reindeer in summer. A year after the first treatment, the mean abundance of H. tarandi was reduced from 3.5 to 0.6, but a year after the second treatment the mean abundance unexpectedly had increased to 4.5. After one year without treatment, the mean abundance and prevalence of the three target parasites were at the same level, or higher, than pre-treatment levels. The main hypothesis for the failure to eliminate the parasites is that gravid H. tarandi and C. trompe females originating from untreated reindeer in adjacent mainland areas dispersed to the island during the warm summer of 1997 (possibly also in 1998). As these oestrids are strong flyers, it may not be too difficult for them to cross >2-3 km of oceanic waters. There are no good explanations for the failure to eradicate L. arctica, but the results indicate that there may be elements in its life cycle that are unknown. The conclusion of the study is that it may be difficult or impossible to eradicate these parasites permanently, even locally such as on islands unless adjacent areas on the mainland are also cleared.

Influence of timing of endectocidic antiparasitic treatment on its efficacy in overwintering reindeer

To find out if timing of endectocidic antiparasitic treatment is critical for its efficacy in overwintering reindeer, 72 hinds of the Kaamanen Experimental Reindeer Herd were randomly allocated to four groups. Three groups received ivermecrin mixture orally once at a dose of 200 pg/kg, either in September, December, or February, and one group was left untreated. Antiparasitic efficacy was evaluated by counting Hypoderma tarandi and Cephenemyia trompe larvae in April, and by faecal examinanon for trichostrongylid nematode eggs in March and April. Production efficacy consequences were assessed by comparing animal weight development from November to April, and calf birth weights. No difference could be seen in the antiparasitic efficacy of the treatments; all were 100 % efficient against H. tarandi larvae (warbles) and C. trompe larvae (throat bors), and reduced the trichostrongylid egg output by 62 to 74%. Weight gains of the groups were not significantly different, however the calf birrh weights differed nearly significantly (P = 0.057). On average, smallest calves were produced by the untreated group.

Flight capacity of the reindeer warble fly, Hypoderma tarandi (L.), and the reindeer nose bot fly, Cephenemyia trompe (Modeer) (Diptera: Oestridae)

The performance of tethered flies on a laboratory flight mill was used to assess the flight capacity of Hypoderma tarandi (L.) and Cephenemyia trompe (Modeer). Maximum total flying times for H. tarandi females were 31.5 h, but most flies flew < 20 h (mean 8.5 h (SD 7.2 h)). The longest continuous flight was 12 h. For both species, mating greatly altered the flight behaviour of females. Unmated laboratory-reared females were reluctant to fly, and flew less continuously than mated wild-caught flies. Hypoderma tarandi males typically flew for short periods of a few minutes with long rests between flights. Cephenemyia trompe females seldom exceeded 10 h of total flying time (mean 4.9 h (SD 3.2 h), maximum 10.8 h), but were capable of many hours of sustained flight. Field-trapped C. trompe males normally flew < 8 h (mean 2.8 h (SD 2.1 h), maximum 7.1 h). In free flight the speed of C. trompe males was ≈8 m/s. Maximum flight distances during the lifetime of a fly were estimated to be 600–900 km for female H. tarandi, 220–330 km for female C. trompe, and 200–400 km for males of both species. Hypoderma tarandi could maximally reduce its mass to about 40% of initial mass, and the mass loss rate during flight was 3.5-fold that of basal metabolism (i.e., without flying) at 22 °C. The adaptive significance of the extraordinary capacity for sustained flight of female oestrids is related to the migratory behaviour of their vertebrate host, Rangifer tarandus (L.).

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

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.

The mating sites of the reindeer nose bot fly: not a practical target for control

The reindeer nose bot fly Cephenemyia trompe aggregates on hilltops/mountaintops to mate. Although active only for brief periods on certain days, males have been collected only from such sites. To evaluate possible suppression of the fly population by killing males (by insecticides or traps) at such sites, the density of sites and the number of males at each site were monitored in a summer grazing area of the semidomestic reindeer host (Rangifer tarandus) in Finnmark, northern Norway. In an area of ca. 20 km2, 19 mating sites were detected and examined during 4 hours on one day. The number of males observed at most sites was 5-16 (range 3-60). Minor hilltops had few males but at some sites &gt;20-60 flies were dispersed over an area of at least 100 m2. It is concluded that mating sites in the study area are too numerous, and also used by many beneficial non-target species, to be practical targets for control of the species.