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THE EGGS AND LARVAE OF PACHYBRACHIS PECCANS AND P. BIVITTATUS, WITH A KEY TO THE KNOWN IMMATURE STAGES OF THE NEARCTIC GENERA OF CRYPTOCEPHALINAE (COLEOPTERA: CHRYSOMELIDAE)

Published online by Cambridge University Press:  31 May 2012

Laurent LeSage
Laurent LeSage
Affiliation:
Agriculture Canada, Biosysternatics Research Institute, Ottawa K1A 0C6
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Abstract

The egg and larval instars of Pachybrachis peccans Suffrian and P. bivittatus Say are described and illustrated. Adults of both species appear in late May, feed on willow leaves, mate and oviposit in June–July. The larvae, unable to climb the host plants, feed in the leaf litter of dead leaves of willow; they reach the second-last or last instar by the end of the fall; then they seal their case and overwinter. Pupation occurs the following spring, probably in early May.

Larval instars can be distinguished as follows: first instar with egg bursters on meso- and metathorax, with typical head chaetotaxy consisting of flattened-papillate setae and 1 pair of very long simple setae, and tibiae with 2 pairs of spiniform setae; older instars without egg bursters, and showing differences in size, in head and pronotal chaetotaxy, and in the number of spiniform setae on the tibiae.

In the larvae, the premental sclerites of the head seem to be present throughout the Campsomata, a group with case-bearing larvae and not only in the Lamprosomatinae as previously reported.

Résumé

L'auteur décrit et illustre l'oeuf et les stades larvaires de Pachybrachis peccans Suffrian et P. bivittatus Say. Les adultes des deux espèces font leur apparition à la fin de mai, se nourrissent de feuilles de saule, s'accouplent et pondent de juin à juillet, Les larves sont incapables de grimper aux plantes et se nourissent de feuilles mortes de saule, dans la litière; quand elles atteignent l'avant dernier ou le dernier stade de leur développement à la fin de l'automne, elles scellent leur fourreau et hibernent dans cet état. La nymphose a lieu au printemps suivant, probablement au début de mai.

Les différents stades larvaires peuvent être séparés : premier stade portant des ovirupteurs sur le méso- et le métathorax, ayant une chaetotaxie céphalique faite de soies aplaties-papilleuses en plus d'une paire de très longues soies simples, et possédant deux paires de soies spiniformes sur les tibias; les autres stades larvaires plus âgés n'ont pas d'ovirupteurs et montrent des différences de taille, de chaetotaxie céphalique et pronotale, et de nombre de soies spiniformes sur les tibias.

Chez les larves, les sclérites prémentaux de la tête semblent présents chez tous les Camposomata, groupe dont les larves possèdent un fourreau, non seulement chez les Lamprosomatinae tel que déjà rapporté.

Type
Articles
Information
The Canadian Entomologist , Volume 117 , Issue 2 , February 1985 , pp. 203 - 220
Copyright
Copyright © Entomological Society of Canada 1985

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