The timing and departure rate of larvae of the warble fly Hypoderma (= Oedemagena) tarandi (L.) and the nose bot fly Cephenemyia trompe (Modeer) (Diptera: Oestridae) from reindeer

Abstract

The emergence of larvae of the reindeer warble fly Hypoderma (= Oedemagena) tarandi (L.) (n = 2205) from 4, 9, 3, 6 and 5 Norwegian semi-domestic reindeer yearlings (Rangifer tarandus tarandus (L.)) was registered in 1988, 1989, 1990, 1991 and 1992, respectively. Larvae of the reindeer nose bot fly Cephenemyia trompe (Moder) (n = 261) were recorded during the years 1990, 1991 and 1992 from the same reindeer. A collection cape technique (only H. tarandi) and a grating technique (both species) were used. In both species, dropping started around 20 Apr and ended 20 June. Peak emergence occurred from 10 May - 10 June, and was usually bimodal. The temperature during the larvae departure period had a slight effect (significant only in 1991) on the dropping rate of H. tarandi larvae, and temperature during infection in the preceding summer is therefore supposed to explain the uneven dropping rate. This appeared to be due to the occurrence of successive periods of infection caused by separate periods of weather that were favourable for mass attacks by the flies. As a result, the temporal pattern of maturation of larvae was divided into distinct pulses. Departure time of the larvae in relation to spring migration of the reindeer influences infection levels. Applied possibilities for biological control by separating the reindeer from the dropping sites are discussed

Reindeer summer activity pattern in relation to weather and insect harassment

“…Between early May and June, warble fly larvae leave their host through their breathing hole in the skin (Bergman 1917;Kelsall 1975;Solopov 1989), while nose bot fly larvae are coughed and sneezed out (Espmark 1968). On the ground the larvae pupate, and after a few weeks they emerge as flies, normally from the beginning of July, occasionally during warm summers already in the end of June (Nilssen & Haugerud 1994, 1995Nilssen 1997a,b). After mating, females seek reindeer, and each warble fly may attach 500-700 eggs to the hair of the reindeer fur (Espmark 1968;Savaljev 1968) whereas nose bot flies spray live larvae onto the reindeer muzzle (Anderson & Nilssen 1990) from where they crawl into the nasal cavities and later into the larynx and pharynx regions.…”

Are warbles and bots related to reproductive status in West Greenland caribou?

“…Adult flies are strong fast fliers (Nilssen & Anderson 1995), which make it easy to locate, track and follow their hosts (Iver, et al, 2002). Hot summers increase adult fly activity and thus harassment of caribou (Thomas & Kiliaan, 1990;Folstad et al, 1991;Nilssen & Haugerud, 1994;Mörschell, 1999;Witter et al, 2011). An extreme example of the influence of oestrid flies was the summer of 1977 in north-west Alaska.…”

“…Oestrid flies have a one year direct life cycle, with no intermediate hosts (Savel'ev, 1961;Anderson & Nilssen, 1990;Nilssen & Haugerud, 1994, 1995Nilssen, 1997). Adult flies develop and mate in summer, while larvae over-winter inside reindeer/caribou.…”

Synopsis

“…The adult flies when attacking reindeer are said to help to collect the animals in flocks (e.g. Nilssen & Haugerud, 1994), which is needed for the ear-marking in the summer. Some reindeer herders refuse to believe that the flies would be totally unnecessary and only harmful for reindeer.…”

“…In late March -early May, when the larvae had reached the 3rd instar stage, but before a considerable amount of them had left the host (Nilssen & Haugerud, 1994), the backs of the experimental reindeer were examined visually and by digital palpation (I, III, V, VI, VII). If the number of warbles exceeded 30, the count was done in tens as adjacent warbles might blend together and prevent exact enumeration.…”