Kingdom Animalia Suborder Apocrita Family Braconidae Phylum Arthropoda Rank Species | Class Insecta Superfamily Ichneumonoidea Subfamily Aphidiinae Genus Aphidius Order Hymenopterans | |
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Similar Hymenopterans, Aphidius, Asaphes, Aphidiinae, Macrosiphum euphorbiae | ||
Aphidius nigripes is a species of parasitoid wasp in the subfamily Aphidiinae of the family Braconidae. It parasitises the potato aphid Macrosiphum euphorbiae, and in eastern North America it is the most common parasitoid attacking this aphid.
Ecology
The potato aphid (Macrosiphum euphorbiae) lays its eggs on weeds where they overwinter. They hatch from mid-April to mid-May and Aphidius nigripes also emerges and starts to parasitise the aphid while it is still on the primary host. Around June, the aphid moves to its secondary host, the potato, and the wasp accompanies it.
The female Aphidius nigripes emits pheromones soon after emerging from the pupa and these attract winged males. The female only mates once, storing the sperm. She oviposits eggs into the immature stages of the potato aphid and controls the sex of the offspring by either laying a fertilized (female) egg or an unfertilised (male) egg. She seems to preferentially allocate unfertilised eggs to the earliest instars that she parasitises, resulting in more male offspring occupying smaller aphid nymphs. Ovipositing in later stage instars predominately produces female offspring; this arrangement is advantageous to the wasp because the energetic requirements for the female in finding aphid hosts and laying eggs is greater than that required by the male. It has been shown that small and large males are equally successful in mating and produce similar numbers of progeny.
The developing wasp larvae feed on the tissues of their hosts, avoiding the vital organs as far as possible. When the wasp larvae are nearly ready to emerge, they control the behaviour of their hosts in different ways depending on the time of year. Those that are ready to emerge early in the season cause their host aphids to climb onto the upper surfaces of leaves, where hosts and parasites may develop faster in a warmer position, and where the wasp larvae are less likely to become the victims of hyperparisitism. Larvae completing their development late in the year cause the aphids to crawl downwards and find concealed spots. Here the wasp larva forms a cocoon inside the hollowed-out body of the host, spends the winter as a diapausing larva known as a prepupa, and pupates in the spring.