Trapping oestrid parasites of reindeer: the response of Cephenemyia trompeand Hypoderma tarandi tobaited traps

Abstract

At 340-360 km North of the Arctic Circle in Norway, Hypoderma tarandi (L.) and Cephenemyia trompe (Modeer) females were caught in baited traps from 10 July to 21 August. During three summers, adverse climatic conditions inhibited flight activity of these oestrids on 56-68% of the days. Flies were not caught prior to or after these dates, nor at winds above 8 m/s, temperatures below 10 degrees C, light intensities below 20,000 lux, or during periods of rain or snow. CO2-baited insect flight traps caught significantly more H.tarandi females than non-baited traps. However, neither a white reindeer hide or reindeer interdigital pheromone glands enhanced the attraction of CO2 to H.tarandi or C.trompe. Hypoderma tarandi females also were attracted to mobile people, but not to stationary individuals. There were no significant differences in the number of C.trompe or H.tarandi caught in CO2-baited traps in a birch/willow woods, on the treeless vidda (= tundra-like biome), or at woods:vida ecotone sites. Flies were caught in traps on days when the nearest reindeer herds were 25-100 km away. Significantly more H.tarandi and C.trompe were caught from 09.30 to 14.30 hours than from 14.30 to 19.30 hours; no flies were caught from 20.00 to 07.00 hours (Norwegian Standard Time = NST). Because of CO2-baited traps caught from hundreds to thousands of mosquitoes, blackflies and Culicoides midges, when climatic conditions inhibited oestrid activity, reindeer aggregations and movements attributed to insect attacks during warm sunny days may be largely in response to attacks by H.tarandi and C.trompe.

Do reindeer aggregate on snow patches to reduce harassment by parasitic flies or to thermoregulate?

“…All trapping was conducted on warm, sunny days having low wind velocities. We used insect flight traps (2.2 m h X 1.6 m w), in which most insects are trapped in a clear apicallymounted collecting container (Anderson & Nilssen, 1996). Each trap was baited with 4 -6 kg of dry ice per trapping period.…”

“…Breev (1950) also collected and identified samples of the parasitic fly fauna that attacked tethered reindeer in USSR. Recent trapping studies (Helle et al, 1992;Anderson & Nilssen, 1996) found that the fly species caught in C02-baited traps, as well as their relative abundance (Helle et al, 1992), was the same as those caught attacking tame reindeer.…”

“…Moreover, during most days, arctic/subarctic climatic conditions are unfavorable for fly activity (Thomson, 1971;Skogland, 1984;Anderson & Nilssen, 1996), thus limiting opportunities to assess interactions between caribou/reindeer and their associated dipteran parasites. Because quantitative sampling of parasitic flies attacking animals under these field conditions has not been possible, inferred assessments of "insect" abundance have been based on: 1) descriptive observations of animal behavior associated with the use of a temperature/wind velocity index to estimate the severity of insect harassment (e.g.…”

“…During insect trapping studies in 1984 (Anderson & Nilssen, 1996), we observed reindeer aggregations on SP's in distant mountains on warm, 4 sunny days, and in subsequent years we operated insect traps in an accessible area having temporary summer SP's.…”

Insect avoidance may override human disturbances in reindeer habitat selection

“…During warm weather, harassment by warble flies, nose bot flies (the oestrids Hypoderma tarandi L and Cephenemyia trompe L. respectively), species of Tabanidae, mosquitoes (Aedes spp., Culicidae), and species of Simuliidae (all hereafter referred to as harassing insects), influences habitat choice of Rangifer tarandus. The insect harassments are usually most severe during the oestrid flight season from late June until the early and mid August (Anderson & Nilssen, 1996;Nilssen, 1997;Anderson et al, 2001). In periods of insect harassment, R. tarandus are often considered to walk against the wind while foraging and to move towards higher grounds and summits (White et al, 1975;Anderson & Nilssen, 1998;Hagemoen & Reimers, 2002).…”