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SUMMARYWork on the nature of the factors selecting against the melanie morphs of Adalia bipunetata is reviewed, New data are presented showing that there is normally one generation per year in Great Britain and that the cyclical changes in morph frequency observed in Berlin may not occur in Great Britain.The roles of migration and selective predation in limiting the spread of the melanie morphs are discussed and evidence is presented to show that predation by birds on ladybirds occurs more frequently than previously supposed.In conclusion it is proposed that the melanie frequency of a population is the result of the interaction of a number of factors whose importance varies from locality to locality.

SUMMARYThe nature of the factors maintaining the colour polymorphism in Adalia bipunctata has been the subject of much discussion and in some populations a tendency for the melanic morphs to mate more frequently than the nonmelanics has been reported. The morph frequencies among mating pairs in wild populations of A. bipunctata in England have been scored and analysed in order to discover whether mating between morphs is a random process. Data from the literature are also analysed in the same way and the methods of analysis adopted by earlier workers are discussed. It is concluded that mating between morphs is frequency dependent so that it is the rare morph irs the population, regardless of colour, which mates more frequently. This appears to be a further method by which the polymorphism in this species is maintained.

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A malathion-resistant strain of Oryzaephilus surinamensis (L.) was subjected to selection with malathion for ten generations at three doses, 65, 260 and 390 mg/m 2 . The relative fitness of the resistant homozygote, the heterozygote and the susceptible homozygote were estimated at each dose and in an untreated control population by comparing the change in frequency of the susceptible homozygote from generation to generation. In the absence of the insecticide, the resistant genotypes had a fitness coefficient of 0-82 compared to the susceptibles, whereas following selection at the highest dose of malathion, the fitness coefficient of the susceptible homozygote was 0 and that of the heterozygote 0-4, compared to the resistant homozygote. With selection at the highest dose of malathion, the frequency of the resistance gene rose from 0-5 to around 1-0 during the experiment, and this was accompanied by a 2-3-fold increase in the resistance factor at the ED50. A model is provided to show how the data collected in these experiments can be used to predict the increase in resistance under various treatment regimes. The model shows that although resistance would be delayed longest at the lowest dose, such a dose would fail to control the pest population. Using the data from these experiments, the model predicts that the best combination of control and delay of the spread of resistance would be achieved by using the highest dose of malathion while allowing the maximum acceptable proportion of beetles to remain untreated.

A survey of five species of moth each showing different degrees of melanism was made in Greater Manchester and compared with samples from adjacent rural areas. The genetics of the various systems is discussed