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Old World rodents Gerbillus gerbillus and Mus musculus and New World mice Peromyscus leucopus and P. maniculatus were susceptible hosts to larvae of the rodent bot fly Cuterebra fontinella . There were no differences because of sex in the susceptibility of previously uninfested (Pu) P. leucopus , the natural host of C. fontinella. P. leucopus acquired a partial resistance 5 weeks after infestation, whereby the rate dropped from >80% among Pu mice to ca 50% in previously infested (Pi) mice. Mice were sensitized by larvae that entered naturally via the nares or anus, but not when introduced through the eye or by subcutaneous injection in the back. The level of resistance acquired was not related to the number of larvae in an exposure or number of exposures, but more than 1 larva was required to provoke a response in Pi mice. Mice in which the infestation was aborted after 2 days (larvae had not completed migration) were less resistant to reinfestation than mice that underwent a mature infestation.

First-instar larvae of the common cattle grub, Hypoderma lineatum , implanted in the backs of laboratory white mice usually migrated to the thoracic and abdominal cavities where they were encapsulated by fibrous tissues of the host. These larvae did not grow but some survived at least 10 months. Mice died as a consequence of myiasis only during the first 3 weeks after the implantation. Apparently, migrating larvae frequently caused lethal lesions in the host's vital organs.

White mice fed a vitamin A-deficient diet for 30 days were more susceptible to percutaneous infestation by larvae of Hypodenna lineatum than mice fed complete, pyridoxine-deficient, low-protein (6%), or gelatin-mucin-supplemented diets. Also, the rate of survival of larvae was higher in mice injected twice with 0.5 ml of rabbit antimouse lymphocyte serum and treated with whole-body irradiation (400 rad) than in untreated mice. The largest larvae found in mice fed on the granulomatous tissues of the host surrounding them, and their digestive tracts appeared normal; the midgut epithelium of smaller larvae appeared to be nonfunctional.

The mean levels of vitamin A in the serum of 6-month-old Hereford calves fed complete or vitamin A-deficient diets for 85 days were 51.6 and 14.0 μ/100 ml, respectively. The animals deficient in vitamin A were more susceptible than normal animals to infestation by larvae of Hypoderma lineatum that hatched from eggs laid on the hair (39.7 vs 21.2% recovery of larvae) but not to infestation by similar numbers of newly hatched larvae injected subcutaneously (57.9 vs 52.7% recovery of larvae). Avitaminosis A apparently reduced the resistance of calves to percutaneous invasions by the parasites.