by K. Fondren Department of Entomology, Michigan State University, East Lansing, MI 48823
Brown lacewings may be less commonly observed than the green lacewings (Neuroptera: Chrysopidae), but they are also important predators of aphids and other small soft-bodied insects. Most of the Hemerobiidae look superficially alike. The most common genus occurring in the United States is Hemerobius. The most common species of Hemerobius is H. stigma (=stigmaterus) Stephens.
Hemerobius stigma is widely distributed across most of North America and is themost common conifer-inhabiting brown lacewing in most of its range (Klimaszewski and Kevan 1985). It is relatively large for a brown lacewing (5.0-7.5 mm). The fore wings are narrowly oval with a slightly pointed apex. Color is a light reddish brown to brownish grey. A close look at the wing venation can distinguish it from most other Hemerobius species. Species determinations, however, can only be confirmed by expert examination of the genitalia (Klimaszewski and Kevan 1985).
Typically, brown lacewings become active earlier in the season than green lacewings. They tend to prefer arboreal habitats such as coniferous and deciduous forests, plantations, or orchards. Hemerobius stigma is particularly associated with conifers (Throne 1971).
All brown lacewings are voracious predators as both larvae and adults. Prey includes tree-dwelling insects such as aphids, adelgids and other small soft-bodied insects. H. stigma is often found in association with the balsam twig aphid (Mindarus abietinus Koch) in Christmas tree plantations. It is also an important predator of the balsam woolly adelgid (Adelges piceae) and pine bark adelgid (Pineus strobi). Laidlaw (1936) recommended it for control of Cooley¹s spruce gall adelgid (Adelges cooleyi) on Douglas-fir. It is known to attack a variety of conifer-feeding aphids (McGugan and Coppel 1962; Laidlaw 1936).
H. stigma overwinters as an adult or prepupa (Laidlaw 1936). It becomes active as early as March in Wisconsin (Throne, 1971) or April in Quebec (Garland 1981b). Active adults have even been observed in December and February in British Columbia (Klimaszewski and Kevan 1985). In early spring, the adults mate and eggs are deposited about two weeks later. The adult females and the eggs are extremely cold-tolerant (Garland 1981b). Eggs are laid singly, on fir needles or between bud scales. Eggs hatch in about 11 days, depending on the temperature (Klimaszewski and Kevan 1985).
Most hemerobiids have three larval instars. All instars are active feeders. They are relatively slender, with a small head and jaws compared to chrysopid larvae (see chrysopid page). After the third instar, the larva forms a pupa in a silk cocoon. The pupal stage lasts about 9-14 days in the summer. Two generations per year are most common, although temperature can play a significant role.
Hemerobius species have great potential as biological control agents for several reasons: the adults are long-lived and have a high reproductive capacity, both larvae and adults have voracious appetites, and their prey includes many pest species (Klimaszewski and Kevan 1985).
As with most beneficial insects, brown lacewings are susceptible to broad-spectrum insecticides.
Conservation appears to be the best way to encourage populations of brown lacewings in the field. Avoiding insecticide use when lacewings are present and encouraging forested windbreaks or trees along field edges may be helpful. Adults are easy to scout by foliage beating over a sheet --they have a 'drop dead' response when disturbed and will remain motionless for a short time. Use this scouting method to determine if lacewings are present and active in early spring.
Currently, brown lacewings are not reared commercially. Mass rearing of brown lacewings is difficult, requiring huge numbers of aphids (Garland 1981a).
Garland, J.A. 1981a. Effect of low-temperature storage on oviposition in Hemerobius stigma Steph. (Neuroptera: Hemerobiidae). Entomol. Mon. Mag. 116: 149-150.