(040509 revised,040509 created)

Clarke CA, Sheppard PM.: Genetic and environmental factors influencing pupal colour in the swallowtail butterflies Battus philenor (L.) and Papilio polytes L.; J. Entomol. (A) 46:123-33 (1972).

It has been suggested that environmentally controlled polymorphisms are likely to arise when there is as mosaic of distinct environments and the particular environment experienced by an individual is uncorrelated with that experienced by its parents. The green and brown colour phases of the larvae and pupae of some Lepidoptera seem to constitute such polymorphisms.

The pupae of Battus philenor (L.) found in the wild in California were either green or brown, and the colour showed a correlation with the background on which the pupa rested. However, the correlation was not complete, since some pupae on a brown background (particularly if it was a thin stem) were green.

Two populations of Papilio polytes L. were kept living free in two greenhouses. A study of the green and brown colour phases of their pupae showed that the colour was affected by the environment and that, as with B. philenor, there was a correlation between background colour and pupal colour. Furthermore, like the situation in B. philenor, the correlation was not complete, some green pupae being found on brown surfaces.

It is suggested that in the absence of an appropriate environmental stimulus the pupa will be green, but in its presence the pupa will be brown. The time at which the environmental factor is effective appears to be between the choosing of the pupation site by the larva and pupation itself. It is further suggested that an incorrect match between the colour of the pupa and the background results from an insufficiently large environmental stimulus, which therefore fails to elicit the production of the appropriate hormone for the deposition of brown pigment.

Selection experiments in the two populations were undertaken, one population being selected for correct matching between pupae and their backgrounds, the other for incorrect matching. This selection failed to alter the sensitivity of the switch mechanism to the environmental factor, but did alter the pupation sites chosen by the larvae. Thus at least it is possible to alter the proportion of green pupae on a brown background by selection acting on larval behavior. It is concluded that in the wild the proportions of green and brown pupae on green and brown backgrounds are held close to their optimal values by the operation of natural selection.