Observations on the behaviour of Dermacentor andersoni larvae infesting normal and tick resistant guinea-pigs.

In three separate experiments the behaviour of Dermacentor andersoni larvae on normal and tick-resistant guinea-pigs was studied at intervals throughout 5-day infestation periods. Fewer larvae survived on resistant hosts and their mean sizes were less than those of larvae on normal hosts, the differences becoming more obvious as time progressed. When measured at 32 degrees C, the peristaltic rates of midgut diverticula of the larvae surviving on resistant hosts were consistently lower than those of larvae from normal hosts. Mean surface temperatures of infested ears were higher on resistant than on normal hosts. This was assumed to be a result of cutaneous hypersensitivity reactions in the resistant animals. Larvae detached, or changed attachment sites, more often on resistant than on normal hosts. This was consistently evident after 26 h post-infestation and correlated with the known timing of basophil cell infiltration and degranulation in the skin of infested, resistant guinea pigs. It appeared that most larvae, after detaching from the resistant host, died off the host. However, some died in situ while still attached. Such deaths occurred on resistant but not on normal animals between 8 and 26 h post-infestation.