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  • B. Bai (a1)

Conspecific host discrimination and larval competition in two aphid parasitoid species were studied in the laboratory using the pea aphid, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), as a host. Aphidius ervi Haliday (Hymenoptera: Aphidiidae) used internal host cues to discriminate between unparasitized and conspecific parasitized hosts. When only parasitized hosts were available, females oviposited into recently parasitized ones where their progeny had a good chance to survive, but rejected those parasitized ≥24 h earlier where their offspring normally died. Competitions occurred only after both eggs had hatched. Larvae eliminated supernumeraries by means of physical combat and physiological suppression. In Aphelinus asychis Walker (Hymenoptera: Aphelinidae), factors, or changes in host internal condition, associated with hatching of the first egg resulted in suppression of conspecific competitors which could be in either larval or egg stage. The older larvae always won competitions through physiological means. A wasp’s oviposition decision is shown to be influenced by the probability of its progeny’s survival. Species that have different reproductive strategies may respond differently to identical host conditions.


La discrimination des hôtes par des individus de la même espèce et la compétition entre larves de deux parasitoïdes du puceron du pois ont été étudiées au laboratoire, en utilisant le puceron du pois, Acyrthosipon pisum (Harris) (Homoptère : Aphididae), comme hôte. Aphidius ervi Haliday (Hymenoptère : Aphidiidae) utilisait des indications internes pour distinguer les hôtes non parasités de ceux parasités par des guêpes de la même espèce. Lorsque les hôtes parasités étaient seul disponibles, les femelles déposaient leurs oeufs dans ceux qui étaient les plus récemment parasités dans lesquels leur progéniture avait une meilleure chance de survivre, mais rejetaient ceux parasités plus de 24 h plus tôt où la descendance mourait. La compétition avait lieu seulement après éclosion des oeufs. Les larves de l’espèce en plus grand nombre étaient éliminées par combat physique et suppression physiologique. Dans Aphelinus asychis Walker (Hymenoptère : Aphidiidae), les facteurs associés à l’éclosion du premier oeuf entrainaient la suppression des compétiteurs de la même espèce qui pouvaient être soit au stade larvaire, soit à l’état d’oeuf. Les larves les plus âgées gagnaient les compétitions toujours par des moyens physiologiques. Il a été montré que la décision d’une guêpe de déposer un oeuf est influencée par la probabilité de survie de la progéniture. Des espèces ayant différentes reproductives stratégies pourraient repondre differemment à d’identiques conditions d’hôtes.

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The Canadian Entomologist
  • ISSN: 0008-347X
  • EISSN: 1918-3240
  • URL: /core/journals/canadian-entomologist
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