Discrimination of host sex by a haematophagous ectoparasite

Sex biases in parasite infestation are known for various host-parasite systems. In most cases, males of higher vertebrates are infested by more parasites than females. The mechanisms behind male-biased infestation may include not only more opportunities for males to encounter parasites and/or better performance of a parasite in male hosts but also active selection of these hosts by a parasite. To test this hypothesis, we studied behavioural responses of the flea Xenopsylla ramesis to males and females of its common rodent host Meriones crassus in Y-maze trials. We asked whether an individual flea is able to discriminate between male and female hosts and choose a male host, and whether previous experience of the fleas (never fed, fed once on a male host, fed once on a female host) affects the choice. Among 385 fleas, 62% made a choice. In general, proportions of female fleas making or not making a choice of a rodent did not differ significantly, whereas the majority of male fleas chose a rodent. Latency of rodent choice was similar between male and female fleas, but was strongly affected by experience: fleas that previously fed on a male rodent or were never fed made their choices significantly faster than fleas previously fed on a female rodent. Among fleas that made a choice, selection of a male versus a female rodent depended on flea sex only. Male fleas chose randomly between a male and a female rodent, whereas female fleas chose a male rodent significantly more often than a female rodent. Our results suggest that male-biased flea infestation may involve active choices of male hosts by fleas.