Published online by Cambridge University Press: 31 May 2012
A true understanding of the evolution of the morphological characters of the tortricid larva, and hence of the phylogeny of the species, requires study of early as well as late instars. The characters of the first instars of about 20 species are compared with those of later instars. Postembryological changes and their significance are discussed for the head, the coronal suture, the ocelli, the spinneret, the body, the spiracle, the anal shield, the anal fork, the crochets, the integument and sclerotized areas, and the setae. Characters of the primitive larva are postulated, and it is concluded that this larva probably lived in a protected habitat, mining some part of its host plant, and had a convenient exit from which it could eject the frass. The evolution of some of the tortricid tribes as indicated by larval characters is also tentatively suggested: the Olethreutinae could have evolved from the Tortricinae as a result of the suppression «f the anal fork on the primordial tortricid ancestor; the reappearance of the fork not too long after its suppression resulted in the Olethreutini, and its continued suppression resulted in the Eucosmini and Laspcyresiini. The Archipini and Sparganothini appear to be the most specialized of the tribes examined of the Tortricinae, and the Laspeyresiim the most specialized of the Olethreutinae, with Laspeyresia Hbn. group 1 possibly being among the most recently evolved in the Tortricidae.
The inferences in this paper are drawn from: examination of the setal arrangements of a few first instars, the chaetotaxy of which is presumed to be an expression of the phylogenetic past of the larva; the fundamental setal arrangements on those larvae that, in late instars, show undoubted structural specialization; deductions as to the original arrangements of setae on the posterior abdominal segments by comparison with that on the primitive middle abdominal segments; the structural changes that occur between early and late instars and between generalized and specialized larvae; and lastly, a knowledge of the life histories of some of the species examined.
It is hoped that the discussion supporting these inferences will enable us to better understand (a) the changes occurring in larval characters not included here, (b) the phylogeny of other tribes of the Tortricidae, and (c) the larval structural changes and phylogeny of other families in the Microlepidoptera.