Abstract
High host density combined with climate change may lead to invasion of harmful parasites in cervid (host) populations. Bot flies (Diptera: Oestridae) are a group of ectoparasites that may have strong impact on their hosts, but data on the current distribution, prevalence and intensity of the moose nose bot fly (Cephenemyia ulrichii) in Scandinavia are lacking. We estimated prevalence and intensity of nose bot fly larvae in 30 moose from southern and 79 moose from central Norway. All larvae detected were identified as the moose nose bot fly. We found surprisingly high prevalence in these areas, which are up to 1300 km south-southwest of the first published location in Norway and west of the distribution in Sweden. Prevalence (0.44–1.00) was higher in areas with higher moose density. Parasite intensity in hunter killed moose was higher in central Norway (mean 5.7) than southern Norway (mean 2.9), and in both regions higher in calves and yearlings than adults. Fallen moose had higher parasite intensity (mean 9.8) compared to hunter killed moose in the subsample from central Norway, suggesting a link to host condition or behavior. Our study provides evidence of parasite range expansion, and establishing monitoring appears urgent to better understand impact on host populations.
Highlights
Parasites influence the fitness of hosts through their effects on indi vidual life-history components (Anderson and May 1978; Gulland, 1992; Irvine et al, 2006)
We explore whether parasite prevalence and intensity correlates with body mass in one of the regions, and contrast the prevalence and intensity of bot fly larvae in hunter killed moose and moose found dead for other reasons
We identified only moose nose bot fly larvae (C. ulrichii), and overall parasite prevalence was 0.72 (n = 109), while overall parasite intensity of infected moose averaged 5.8 larvae per individual (Table 1)
Summary
Parasites influence the fitness of hosts through their effects on indi vidual life-history components (Anderson and May 1978; Gulland, 1992; Irvine et al, 2006). In the Fennoscandian countries, Norway, Sweden, and Finland, moose (Alces alces) densities have increased rapidly since the 1960s and are currently in general high (Lavsund et al, 2003), varying among regions and countries. Both high host densities and climate warming can facilitate the expansion of parasite distribution ranges. For adult moose it is assumed that infestation with the moose nose bot fly (Cephenemyia ulrichii) larvae is rarely lethal, but that the general health condition may deteriorate markedly. For calves mortality may be higher when they are infested with a great number of larvae (Zumpt, 1965)
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