NONRANDOM MATING IN ADALIA-BIPUNCTATA (THE 2-SPOT LADYBIRD) .2. FURTHER TESTS FOR FEMALE MATING PREFERENCE

Tests for non-random mating in laboratory stocks of Adalia bipunctata showed that female two-spot ladybirds from 'isofemale lines', which had formerly mated preferentially with melanic males, now mated at random. In an attempt to obtain new stocks in which females mated preferentially, we isolated 'isofemale lines' from a natural population at Keele, but we found no evidence of females mating preferentially within these stocks. We did, however, observe two interesting phenomena, not previously reported from Keele populations of Adalia bipunctata, or from laboratory stocks derived from the Keele population. Firstly, much of the variation in male mating success. which we observed, could be explained by the date on which the mating tests were carried out. Secondly, there was significant heterogeneity in sex ratios among some of the stocks. We discuss the potential importance of both these phenomena when designing experiments and interpreting data regarding non-random mating in Adalia bipunctata.