The effect of bot fly larvae on reproduction in white-footed mice, Peromyscus leucopus

Abstract

The effect of bot fly larvae on reproduction in white-footed mice (Peromyscus leucopus noveboracensis) was determined from a sample of 1050 mice that were snap-trapped over a 2-year period in E-central Minnesota. Bot fly larvae (Cuterebra fontinella Clark, 1827) were found parasitizing mice from 16 July through 2 October. During July, August and September, 9.2% of the mice trapped were parasitized by C. fontinella; the mean infestation rate was 1.4 larvae per infested mouse. A single bot fly larva (or scar) was found on 69.1% of the parasitized mice; 23.7% of the mice carried two larvae; 6.2% carried three larvae, and 1.0% had four larvae. More male mice were trapped than females (56.3%–43.7%) and, correspondingly, 55.4% of the bot fly larvae were found on male mice and 44.6% on females. Older mice were more heavily parasitized than younger mice. Parasitized subadult male mice had smaller testes, epididymides and seminal vesicles than nonparasitized subadult males. In adult male mice, the presence of one larva had little effect on the size of the reproductive organs. In adult female mice, parasitism by bot fly larvae did not cause a decrease in the number of embryos, corpora lutea or placental scars. Spleen size increased greatly when larvae were present. The hypothesis is presented that this host-parasite relationship is stable and that the host and parasite have evolved coadaptations and a tolerance for each other.