Summary
The nature of the selective forces operating on M. unipunctatus abdominal colour morphs are examined using two forms of multiple regression analysis, one based upon 11 environmental variables measured at 42 localities in northern England, the other on five principal components generated from them. Results point to the importance particularly of visual selection by predators for crypsis but also of climate.
Aviary and mark release recapture experiments, although not statistically significant, provide direct evidence that birds predate M. unipunctatus with regard to their cryptic efficiency. In both experiments more dark than light insects were taken on lichen-covered rural branches while the reverse, i.e. more light than dark insects taken on lichen-free urban branches, was evident in field experiments only.
Comparisons of morph developmental rate in the field suggest that climatic selection may operate differentially upon the two morphs since dark adult females are heavier than light ones during the pre-oviposition period at the four localities sampled in Yorkshire.
The abdominal colour polymorphism appears to be stable in Yorkshire at present and two systems by which it may be maintained are discussed.
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Popescu, C. Natural selection in the industrial melanic psocid Mesopsocus unipunctatus (Müll.) (Insecta: Psocoptera) in northern England. Heredity 42, 133–142 (1979). https://doi.org/10.1038/hdy.1979.17
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DOI: https://doi.org/10.1038/hdy.1979.17
