Some Special Features of the Leaf-Rolling Technique of Byctiscus Populi L. (Coleoptera, Rhynchitini)
Author: Daanje, A.
Source: Behaviour, Volume 53, Numbers 3-4, 1975 , pp. 285-315(31)
Abstract:Females of the weevil Byctiscus populi construct rolls from young poplar leaves. Within these rolls the eggs are deposited and the larvae develop by feeding upon the innermost leaf-coils. By boring a hole in a petiole or young twig, one or more leaves will fade, and are ready to be wrapped up. About 95% of the rolls constructed are preceded by the boring of a hole in a petiole (P-rolls) ; these rolls each consist of a single leaf. For the construction of the other rolls (5%), a hole is bored in a young twig; these rolls may contain a single (T-rolls) or a few leaves (TT-rolls). Only when one or more of the faded leaves droop within reach of a newly constructed T-roll, may the female wrap up one or more extra leaves into that roll and by so doing a TT-roll arises (in about 29% of the cases in which holes are bored in twigs). The construction of P-, T- and TT-rolls respectively is described and compared. T- and TT-rolls can almost only be made at the beginning of the reproductive season, when the shoots are still soft enough for the females to bore holes in them. In correspondence with the softness of the shoot, are the rolls made from very young soft leaves. Contrary to this, P-rolls can be made during the whole season (from May until the end of August) from slightly less soft young leaves. By eating from a selected leaf, the female is able to discriminate between very young leaves - followed by boring in twigs - and other young leaves - followed by boring in petioles. The size of the food supply for the larvae depends on the size of the wrapped up leaf. The leaves in P-rolls are generally larger than those in T- and TT-rolls, but the nutritional value of the leaves in T- and TT-rolls is greater than that of leaves in P-rolls. Nevertheless, relatively more reproductively fit weevils develop from P-rolls than from T-rolls, whereas TT-rolls resemble P-rolls in this respect. Hence, the more T-rolls are transformed into TT-rolls, the lower the reproductive disadvantage from the construction of T-rolls. In spite of the above reproductive disadvantage and of the fact that the construction of T- and TT-rolls requires more effort and time than that of P-rolls, at the beginning of the reproductive season the females preferably construct T- and TT-rolls. This apparent paradox is explained by the discovery that the boring in twigs in May results in the development of secondary shoots in July and August, by which the sharply diminished supply of leaves suitable to be wrapped up is highly increased again. The reproductive season is essentially prolonged by the development of these secondary shoots. Therefore, each of the three kinds of rolls has its own value for the survival of the species.
Document Type: Research article
Publication date: 1975-01-01