Publisher Summary This chapter discusses the endocrine control of insect polyphenism. Polyphenism in insects is associated with some of the most striking and successful life histories. The terms polymorphism and polyphenism have the same meaning, namely intraspecific variation in sets of characters. This phenomenon is seen as an adaptive response that allows genotypes to track short-term cycles of environmental variation and, at the same time, maintains cohesiveness of adapted gene complexes. With recent advances in population genetics, enzymology, genomics, and proteomics, the term polymorphism has now gained a much wider meaning. Polyphenic mechanisms can be described at two levels: cues that serve as proximate triggers of developmental alternatives and endogenous response cascades that drive the developmental responses. Triggering stimuli may consist of external environmental factors, internal genetic factors, or a mixture of the two. Endogenous response cascades involve a series of systems that relay, synchronize, and coordinate differentiated processes in target systems.

Endocrine Control of Insect Polyphenism

Summary

Green light (510–565 nm) constitutes a significant portion of the visible spectrum impinging on biological systems. It plays many different roles in the biochemistry, physiology and structure of plants and animals. In only a relatively small number of responses to green light is the photoreceptor known with certainty or even provisionally and in even fewer systems has the chain of events leading from perception to response been examined experimentally. This review provides a detailed view of those biological systems shown to respond to green light, an evaluation of possible photoreceptors and a review of the known and postulated mechanisms leading to the responses.

Effects of green light on biological systems.

11.1. Polyphenism and Polymorphism: Discontinuity in the Variation of Insects 464 11.2. Polyphenism in the Hemimetabola 465 11.2.1. Hemiptera/Homoptera Wing Polyphenism 465 11.2.2. Orthoptera 470 11.2.3. “Isoptera” (Termites) — Caste Polyphenism in the Hemimetabola 476 11.3. Polyphenism in the Holometabola 479 11.3.1. Lepidoptera 479 11.3.2. Coleoptera — Male Dimorphism for Weaponry 484 11.3.3. Hymenoptera — Caste Polyphenism and Division of Labor 487 11.4. Synthesis and Perspectives 501

3.13 – Endocrine Control of Insect Polyphenism

. 1. Some swallowtail butterflies produce both green and brown pupae. The phenotypes result from the joint action of genotype and environment and usually make the pupae cryptic in their habitats.



2. The major environmental cues influencing pupal colour in two swallowtail species were determined to be textural and optical.



3. Differences in the usage of these kinds of cues in the two species are thought to have evolved because of major differences in the pupation habitats. P.polyxenes, which usually pupates on slender stems amidst vegetation, responds more strongly to optical cues. B.philenor, which usually pupates on exposed surfaces of tree trunks and cliffs, responds more strongly to textural cues.



4. Differences in the overall tendency to produce brown pupae (‘sensitivity’: Hazel, 1977) are thought to be related to the frequency of brown pupation sites utilized by these two species: high average sensitivity in philenor, which often uses brown sites, and lower average sensitivity in polyxenes, which often uses green sites.

Environmental control of pupal colour in swallowtail butterflies (Lepidoptera: Papilioninae): Battus philenor (L.) and Papilio polyxenes Fabr.

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.

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

59. Jg., He]l 6, 1972 Kurze Originalmitteilungen 219 All groups showed a significant increase (Fig. 1) in testis size compared with the winter controIs (p < 0.00t, U test). Testis development was most advanced in the two long-day groups that did not receive melatonin; each of these groups differs significantly from all other groups (p < 0.0t or < 0.00t). In the long-day animals which received melatonin, testis develop- ment corresponded with that of the three short-day groups (no significant differences). Spermatogenic activity, deter- mined by the number of motile spermatozoa in smears from the cauda epididymidis, corresponded well with testis size. Good correspondence between testis size and histological stage has previously been reported in the golden hamster [7]. These data show that a long photoperiod accelerates testicular recrudescense in the dwarf hamster; that melatonin inhibits the influence of the long photoperiod; but that melatonin does not completely suppress testicular development. The experi- ments also suggest that seasonal breeders are better suited for studies of pineal function than the laboratory rat. Thanks are due to Dr. J. Figala, Budejovice, for introducing the hamsters to our laboratory. Received March 9, 1972 [1] Wurtman, R. J., Axelrod, J., Kelly, D. E.: The pineal. New York: Academic Press 1968. -- [2] Reiter, R. J., Era- schini, F. : Neuroendocrinol. 5, 219 (1969).- [3] Reiter, R. J., Sorrentino, S. : Am. Zoologist 10, 247 (1970). -- [4] Rust, C. C., Meyer, R. I<.: Science 16S, 921 (t969). -- [5] Herbert, J., in: The pineal gland (G. E. "vV. Wolstenholme and J. Knight, eds.), p. 303. Edinburgh: Churchill Livingstone 1971.- [6] Hoff- mann, K.: in prep. -- [7] Gaston, S., Menaker, M.: Science 158, 925 (t967).

C. Wiklund

Papers

Pupal coloration in Papilio machaon in response to the wavelength of light.