Larval morphology and development of Aphidius rhopalosiphi (Hymenoptera: Braconidae: Aphidiinae)1

The aphid parasitoid Aphidius rhopalosiphi is the most abundant species of Aphidiinae in cereal fields in northern Europe. Although the larval morphology of other Aphidiinae has been described, the morphology and immature development of A. rhopalosiphi remain unknown. Our goal is to relate growth and larval developmental stages to morphological changes during parasitoid development, using light and scanning electron microscopy. Aphidius rhopalosiphi develops through three larval stages with clear differences in the morphology of the mouthparts, tegument sculpturing, and respiratory features that can be related to the different constraints that the larvae have to face. In the first instar, adaptations to physical combat with competitors take the form of strong mandibles, active caudae, and dorsal spines that allow crawling motion. In the third instar, the larva is adapted to tear tissues with short hooked mandibles and to face aerial respiration. All instars possess sensory structures. The “three instars” hypothesis is supported here by the observation of larvae in exuviation. No differences were found between our observations and descriptions of other Aphidius species, supporting the idea that species of this genus cannot be distinguished by larval morphology but only by morphometric analysis. Some new features of the genus are presented for the first and second instars. Muratori F, Le Lannic J, Nénon J-P, Hance T. 2004. Morphologie et développement larvaire d’Aphidius rhopalosiphi (Hymenoptera : Braconidae : Aphidiinae). The Canadian Entomologist 136 : 169–180. Résumé—La morphologie des larves de l'endoparasitoïde de pucerons, Aphidius rhopalosiphi, n’a jamais été décrite, bien que certains membres de la sous-famille des Aphidiinae aient fait l’objet d’études morphologiques. Cette espèce d’Aphidiinae est pourtant la plus abondante dans les champs de céréales en Europe du Nord. Notre but est de mettre en relation la croissance et le développement des 169 1 Publication BRC028 of the Biodiversity Research Center, Université Catholique de Louvain, Louvain-la-Neuve, Belgium. 2 Corresponding author (e-mail: [email protected]). J:\ent\ent13602\N03-057.vp March 10, 2004 9:14:21 AM Color profile: Disabled Composite Default screen