Locomotor response to light and surface angle in three species of desert fleas.

We studied the relocation of newly emerged and fed individuals of three species of desert fleas (Xenopsylla conformis, Xenopsylla ramesis, and Parapulex chephrenis) in response to light and surface angle. We observed flea movements inside of either horizontal or tilted cardboard tubes with different light regime at their ends. Proportion of relocating X. conformis and X. ramesis was significantly higher than that of P. chephrenis. In this species only, adult individuals relocated more frequently than newly emerged individuals, and females relocated more frequently than males. In general, the majority of fleas moved toward light independently of its position in relation to the surface angle. Fleas moved toward light even if it was positioned at the lower end of a tube. When both ends of a tube were darkened, newly emerged Xenopsylla moved randomly toward the upper or lower end of a tube, whereas newly emerged P. chephrenis moved mainly toward the upper end of a tube. Adult P. chephrenis and X. conformis also moved mainly toward the upper end of a tube, whereas adult X. ramesis moved mainly toward the lower end. When both ends of a tube were lighted up, newly emerged females of all species, as well as newly emerged female X. ramesis, randomly relocated toward the upper or lower end of a tube. In contrast, newly emerged males and adults of both sexes of P. chephrenis and X. conformis as well as adult female X. ramesis moved mainly toward the upper end of a tube, whereas adult male X. ramesis moved mainly down. Results of this study suggest that light is a more important abiotic signal for flea orientation than surface angle, and there are species-specific differences in flea responses to light and angle stimuli. These differences are related to spatial ecology and behavior of fleas' main hosts as well as to fleas' environmental preferences.