The larvae of many Lepidoptera of the family Noctuidae have both green and brown forms. This trait had never been studied in depth. (Chapter 1) Larvae of Phlogophora meticulosa exhibit considerable colour variation. A method was developed to score larval colour. (Chapter 2) Eight colour types were defined, these being named "early green", "3rd instar green", and the main colour types "green, olive, brown, plain yellow, yellow-green and yellow-brown". Larval colour in the 1st, 2nd and sometimes 3rd instars is determined by foodplant colour. The seven colour types found in the late in stars, (3rd instar green is replaced by the green main colour type in subsequent instars), are controlled by five unlinked major genes which have a total of eleven alleles. The system involves a complex arrangement of dominance and epistatic effects. (Chapter 3) The change from foodplant to genetic control of larval colour is correlated with a change from a positive to a negative phototactic response. (Chapter 4) Study of allelic and phenotypic frequencies in wild populations has indicated that the genetic polymorphism is balanced from year to year, although the frequencies of some alleles show seasonal variation. (Chapter 5) Tests to determine the nature of the selective forces, which maintain the polymorphism, have indicated that choice of mate is random. Heterozygote advantage is implicated in the maintenance of at least two of the genes. (Chapter 6) Selection due to viral infection and parasitism both affect the maintenance of at least one gene, and beetle and small mammal predation may also do so. (Chapter 7) Experiments on the effects of bird predation have uncovered a complicated system of bird-larval morph relationships. (Chapter 8) Arguments are put forward to explain the switch from foodplant to genetic control of colour, and to explain the lack of linkage between the five major genes controlling larval colour. The relative importance of the selective agencies scrutinised is considered. It is suggested that bird predation is extremely important in the maintenance of the genetic system. The degree to which larval morphs are exposed to differential predation by birds is determined by the cryptic qualities of the larvae, and, because birds select apostatically to some extent, their abundance. Further lines of research are suggested (Chapter 9).
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:464697 |
| Date | January 1978 |
| Creators | Majerus, M. E. N. |
| Publisher | Royal Holloway, University of London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://repository.royalholloway.ac.uk/items/d5444756-9612-48ef-995e-d0af8df3a565/1/ |
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