Trapping oestrid parasites of reindeer: the relative age, fat body content and gonotrophic conditions of Cephenemyia trompeand Hypoderma tarandifemales caught in baited traps

Abstract

Dissection of flies caught in northern Norway revealed that only mated, gravid females of H.tarandi (L.) and larviparous C.trompe (Modeer) were caught in host-mimicking CO2-baited traps. Trapped females had the same gonotrophic and fat body (FB) conditions as females caught on and around reindeer. Most trapped females of both species were of middle to old age, having only one-half to no FB reserves left and only a few to moderate numbers of eggs or larvae remaining. Most young females trapped also had previously oviposited or larviposited at least once, and some newly eclosed, mated females were present throughout the fly season. Based on the known location of reindeer herds, it was evident that trapped flies that had recently oviposited or larviposited had dispersed into the trapping area from 25-100 km away. Declining FB reserves sustained wild-caught C.trompe females (and in utero larvae) in the laboratory for 14 days and H.tarandi females for 18 days. Reserve FB also was depleted during long flights. Females of both species that flew for the longest times (5.1-11.7 h) on a laboratory flight mill had low FB reserves, but nearly maximum numbers of eggs or larvae. Conversely, most females that flew for less than 5 h on the light mill had little or no FB remaining, and few eggs or larvae. The large FB reserves accumulated as larvae feed in the vertebrate host enable the non-feeding adults to survive and infect their hosts even after prolonged periods of flight-inhibiting climatic conditions.

Escaping parasitism in the selfish herd: age, size and density‐dependent warble fly infestation in reindeer

“…In the study area, most warble flies pupate and emerge on the spring pastures and have to fly a considerable distance to reach their hosts on the summer pasture ( Fig. 1, Folstad et al 1991et al , Anderson 1996aet al , 1996b. High reindeer density on the summer pasture should according to the dilution hypothesis give improved protection from warble fly infestation.…”

“…For the encounter–dilution effect to prevail the parasites should actively search for hosts, the encounter rate between hosts and parasites should not increase proportionally with group size, and a parasite should only be able to infect one or a few hosts in a group (Mooring and Hart 1992, Hart 1994). A newly eclosed female warble fly has about 600 eggs available that she might oviposit on several hosts during her lifetime (Anderson and Nilssen 1996a,b, Nilssen 1997). A reindeer herd might accordingly be perceived as a gold mine to a warble fly.…”

“…The density of eclosed warble flies is therefore assumed to be highest for the innermost summer pastures (Folstad et al 1991). However, warble flies are excellent flyers with relatively high abdominal fat reserves, which make them capable of flying long distances (>100 km) in order to search for their hosts or for surviving cold periods when they are inactive (Anderson and Nilssen 1996a). Females produce ∼600 eggs (Nilssen 1997), which may be oviposited on several individual reindeer (Anderson and Nilssen 1996a).…”

“…Two circumpolar Oestrid flies (warble fly; Hypoderma tarandi and nose bot fly; Cephenemyia trompe ), hereby referred to as Oestrid flies, commonly attack reindeer during summer. These flies are highly mobile, and they actively seek out reindeer herds (Anderson and Nilssen 1996a,b).…”

Interrelationships between weather, parasitic insects, and barren-ground caribou (Rangifer tarandus groenlandicus) behaviour in Northwest Territories and Nunavut.

“…Oestrid flies appear least tolerant of low temperatures. I trapped oestrids at temperatures ranging from 14.3-21.5° C roughly corresponding to the reported optimum temperatures for oestrid activity of 15-27° C (Kelsall 1968, White et al 1975, Anderson and Nilssen 1996a, Anderson et al 2001). Due to low sample size of trapped oestrid flies, my measurements should not be construed as upper or lower thresholds.…”