by Jay F. Brunner, originally published 1993
This genus contains several members that are important larval parasitoids of lepidopteran pests. Several species of Apanteles attack leafrollers. Apanteles sp. (possibly A. atar) is one of the most common attacking leafrollers in commercial orchards and may play a key role in biological control of leafrollers when combined with mating disruption or soft insecticides.
Apanteles attacks the four leafroller species known as pests of fruit crops in the Northwest. It is likely that larvae of other Lepidoptera serve as alternate hosts for Apanteles outside orchards.
The larva of Apanteles spends most of its life inside the host larva. It is usually only observed after it leaves the host when ready to pupate. At this time it is a typical maggot form and is a creamy white to light green.
The pupa is the life stage most commonly seen. It is contained within a white fuzzy cocoon. It is oblong and about 1/8 inch long (3 to 4 mm). Usually more than one cocoon, and as many as 15, will be found within the leaf shelter constructed by the doomed host larva.
The adult Apanteles wasp is about 1/8 to 3/16 inch long (3 to 5 mm) with a black body and long antennae. The female has a short ovipositor at the end of the abdomen.
Apanteles overwinters inside the leafroller host larva. As the leafroller larva matures in spring, the Apanteles larva begins to grow and feeds on its host’s organs, eventually killing it. When mature, Apanteles larvae leave their host and spin individual cocoons in the leaf shelter that contained the host.
Apanteles cocoons can be found in late May and early June when unparasitized leafroller larvae are beginning to pupate. The host larva’s remains are usually visible as a black, shriveled mass near the parasitoid cocoons. Adult parasitoids emerge in 7 to 10 days. When leafroller eggs of the summer generation hatch, in late June to early July, the adult parasitoids attack newly hatched larvae. Cocoons are again found in late July or early August, and adult Apanteles parasitize small leafroller larvae in the fall before they move to overwintering sites and construct hibernacula.
The presence and abundance of Apanteles can be determined by examining leaf shelters of leafroller larvae in late May and again in late July. Even if the parasitoid has already emerged from the cocoon, its remnants provide evidence of a successful attack.
Apanteles adults are susceptible to broad-spectrum insecticides, which probably accounts for the reduced level of parasitism of summer generation leafroller larvae in commercial orchards. Since Apanteles has not been successfully reared in the laboratory, artificial release in orchards to augment populations does not seem to be an option. However, Apanteles could be conserved and encouraged in orchards where broad-spectrum insecticides are replaced with mating disruption and soft insecticides for pest control.