''Aphidius nigripes'' is a species of parasitoid wasp in the subfamily

Aphidiinae The Aphidiinae are a subfamily of tiny parasitoid wasps that use aphids as their hosts. Several species have been used in biological control programs of various aphids. Biology and distribution Aphidiines are koinobiont endoparasitoids of ad ...

of the family

Braconidae The Braconidae are a family of parasitoid wasps. After the closely related Ichneumonidae, braconids make up the second-largest family in the order Hymenoptera, with about 17,000 recognized species and many thousands more undescribed. One analy ...

. It is the most common parasitoid of the potato aphid ''

Macrosiphum euphorbiae ''Macrosiphum euphorbiae'', the potato aphid, is a sap-sucking pest insect in the family Aphididae. It infests potatoes and a number of other commercially important crops. Distribution ''Macrosiphum euphorbiae'' originated in North America ...

'' in eastern North America. Many other species of aphids may also serve as hosts.

Ecology

Adult ''A. nigripes'' emerge in the spring and find ''M. euphorbiae'' hosts before the aphid moves from its winter food plant, or primary host plant. Around June, the aphid moves to its secondary host, the potato, and the wasp accompanies it. Female ''Aphidius nigripes'' emit

pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...

s soon after emerging from their pupa to attract winged males. The female mates only once, storing the sperm. She oviposits eggs into the immature stages of the potato aphid. Like other

haplodiploid Haplodiploidy is a sex-determination system in which males develop from unfertilized eggs and are haploid, and females develop from fertilized eggs and are diploid. Haplodiploidy is sometimes called arrhenotoky. Haplodiploidy determines the se ...

insects, she can control the sex of her offspring by laying a fertilized (female) egg or an unfertilized (male) egg. There is a trend for ''A. nigripes'' to preferentially allocate unfertilized male eggs to the earlier, smaller

instar An instar (, from the Latin '' īnstar'', "form", "likeness") is a developmental stage of arthropods, such as insects, between each moult (''ecdysis''), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow o ...

s of aphids. Later stage instar aphids are predominantly used as hosts for 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. Size is not important for male success in mating; small and large males produce similar numbers of progeny. The developing wasp larvae feed on the tissues of their

hosts A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places *Host, Pennsylvania, a village in Berks County People * Jim Host (born 1937), American businessman * Michel Host ...

, avoiding the vital organs as far as possible. When the wasp larvae are nearly ready to emerge, they alter the behavior 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. This leads to faster development of the wasp pupa due to increased temperature and decreases their risk of

hyperparasitism A hyperparasite, also known as a metaparasite, is a parasite whose host, often an insect, is also a parasite, often specifically a parasitoid. Hyperparasites are found mainly among the wasp-waisted Apocrita within the Hymenoptera, and in two o ...

. 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 called a prepupa, and

pupa A pupa ( la, pupa, "doll"; plural: ''pupae'') is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in their ...

tes in the spring to continue its life cycle.

References

{{Taxonbar , from=Q2652786 Braconidae Taxa named by William Harris Ashmead Insects described in 1901