Environmental factors influencing pupal colour determination in Lepidoptera I. Experiments with Papilio polytes, Papilio demoleus and Papilio polyxenes

Abstract

In greenhouse populations of Papilio polytes and Papilio demoleus it has been found that there is a greater probability for green pupae to be formed amongst green vegetation and brown ones on brown stems. Experiments have shown that the determination of pupal coloration depends upon variations in the environmental conditions experienced by a pupating larva. In both species the texture of the pupational substrate appears to be an important factor, brown pupae tending to be found on rough surfaces and green pupae on smooth ones. The effect is more pronounced in P. polytes than P. demoleus . Background colour also has some effect in both species though less than texture, and is more important in P. demoleus than P. polytes . Papilio polyxenes also appears to be affected by background colour. Differences in the relative importance of these factors in P. polytes and P. demoleus is interpreted in relation to the time of day a larva selects its pupation site. It is concluded that texture is relatively more important when the selection of a pupation site occurs in the dark as in P. polytes . Relative humidity, temperature and photoperiod also affect pupal colour and may be important relative to seasonal changes during the year. Physiologically the determination of pupal colour depends on the presence or absence of a hormone. Brown cuticle in both P. polytes and P. demoleus is produced following the secretion of hormone from a source in the head prior to the pupational moult. A green cuticle results when the pigmentation hormone is not secreted.