The effect of host resistance on the metabolic rate of engorged females of Rhipicephalus evertsi evertsi.

This study investigated the effect of acquired resistance in guinea-pigs on the metabolic rate of adult females of the tick Rhipicephalus evertsi evertsi. Guinea-pigs were subjected to three successive infestations of ticks and the rate of CO2 production (VCO2) measured in first and third infestation engorged females. Ticks which fed on resistant hosts showed a 52% decrease in mass compared to ticks that fed on naive animals. Reduction in mass was accompanied by a decrease in VCO2 (mlh-1) per tick but an increase in mass specific VCO2 (mlg-1h-1). However, both groups shared a single allometric relationship between body mass and metabolic rate (VCO2). We suggest that the differences in size rather than any factor directly relating to the mechanism of acquired resistance account for the differences in metabolic rate between ticks fed on naive and resistant guinea-pigs.