Hamilton (1967) predicted that in populations in which sibmating predominantly occurs female-biased sex ratios should evolve to avoid local
competition among siblings for mates. Spalangia cameroni
(Perkin), a solitary parasitoid of house fly puparia, produces female-biased sex ratios in the laboratory as well as in the field. Therefore, levels of sibmating of S. cameroni
were investigated to test the validity of sex ratio theory.
Developmental duration of S. cameroni males and females was initially determined to establish whether the sexes emerge at the same time. Since males emerge about 24 h before females, the behaviour at the time of emergence was investigated to establish whether males wait for
Because males and females leave the site of emergence, the behaviour of males was examined in later experiments to establish where mating potentially takes place. Host location behaviour of S. cameroni females was initially tested in the laboratory with odours of hosts (house fly puparia) and host habitat (chicken manure). Males were tested with the same odour sources because females significantly responded to these odours. Results show that S. cameroni males also responded to odours from the hosts, the host habitat, and virgin females. In the Held, males responded to hosts and virgin
females. Therefore, mating presumably takes place in the habitat of hosts. Predictions of mating in the population are that mating is likely to be at random.