Abstract
Nidicolous ectoparasites such as fleas and gamasid mites that feed on small and medium-sized mammals spend much of their time in their hosts' burrows, which provide an environment for living, and often feeding, to their pre-imaginal and/or adult stages. Thus, these ectoparasites should be adapted to environmental conditions in burrows, including high fractional concentrations of C(O.sub.2) (F.sub.(C(O.sub.2))). We examined how a high (F.sub.(C(O.2))) (0.04) affected survival and reproductive success of a hematophagous ectoparasite of burrowing rodents using fleas Xenopsylla ramesis and Sundevall's jirds Meriones crassus. In the first experiment, fleas fed on hosts housed in high-CO2 (F(C(O.2)=0.04)) or atmospheric-C(O.sub.2) (F(C(O.sub2)?0.0004)) air, and were allowed to breed. In a second experiment, fleas were maintained in high CO2 or CO2-free air with no hosts to determine how C(O.sub.2) levels affect survival and activity levels. We found that at high FCO2 fleas laid fewer eggs, reducing reproductive success. In addition, at high F(C(O.sub.2)), activity levels and survival of fleas were reduced. Our results indicate that fleas do not perform well in the FCO2 used in this experiment. Previous research indicated that the type and intensity of the effects of C(O.sub.2) concentration on the fitness of an insect depend on the (F.sub.(C(O.sub.2))) used, so we advise caution when generalizing inferences drawn to insects exposed to other (F(C(O.sub.2))). If, however, FCO2 found in natural mammal burrows brings about reduced fitness in fleas in general, then burrowing hosts may benefit from reduced parasite infestation if burrow air (F.sub.(C(O.sub.2))) is high.