Behaviour of Spalangia Cameroni Males and Sex Ratio Theory

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Abstract
Although Spalangia cameroni is a solitary parasitoid of house fly pupae, it produces female-biased sex ratios in the laboratory as well as in the field. Sex ratio theory suggests that levels of inbreeding in the species may be great enough to have provided the selection pressures for the evolution of female-biased sex ratios and for their maintenance in the population. Males, however, develop faster than females and they leave the natal site within a few hours of emergence (at least in the laboratory). That males may mate away from the natal site is also suggested by their behaviour being influenced (in an olfactometer) by odours from hosts suitable for parasitization and by odours from components of the hosts'' environment (here, chicken manure). Hosts containing S. cameroni females on the point of emergence also influence male behaviour. That males leave the natal site and are located at host patches was confirmed by trapping in the field. The implicatins for sex ratio theory are discussed.