Green Lacewings
Green lacewings are interesting
predatory insects found in most environments. The common green lacewing (Chrysoperla
carnea) occurs
throughout North America, while other species are more restricted in
distribution. 
The
light green adult has long, slender antennae, golden eyes, and large, veined,
gauze-like wings that are 1/2 - 1/3 inch long. It is a slow-flying, nocturnal
insect that feeds on nectar and pollen, and it emits a foul-smelling fluid from
special glands if captured. They are often attracted to lights at night, so you
may see them sitting on your house or garage door if you leave the lights on for
a while. The female lacewing lays eggs usually in groups on leaves, each egg
held away from the leaf surface on the end of a slender stalk. These are fairly
conspicuous –
if you know what you're looking for. A female lays up to 300 eggs over a period
of 3-4 weeks, but often it does not survive that long in the field.
The
larva, commonly called an aphidlion, resembles a green-gray alligator with
mouthparts like ice tongs. An aphidlion seizes and punctures its prey with long,
sickle-shaped jaws, injects a paralyzing venom, and sucks out the body fluids.
After feeding and growing to ½ inch in length during a 2-3 week period, the
larva spins a spherical, white silken cocoon in which it pupates. The adult
emerges in about 5 days through a round hole that it cuts in the top of the
cocoon. It overwinters as a pupa within its cocoon or as an adult, depending on
the species.
An aphidlion is a voracious feeder and can
consume up to 200 aphids or other prey per week. In addition to aphids, it will
eat mites and a wide variety of soft-bodied insects, including insect eggs,
thrips, mealybugs, immature whiteflies, and small caterpillars. Aphidlions will
also consume each other if no other prey are available.
Green lacewings are available from many
commercial suppliers. Once their food source is exhausted they will leave the
area. The predatory larvae feed for 2-3 weeks before they become adults. The
adults must have a source of nectar, pollen, or honeydew to feed on in the
general vicinity of the pest area to stimulate egg laying, or they will leave.
Providing an adequate food supply and suitable adult habitat can contribute to
lacewings remaining and reproducing in your backyard. Additional releases can
provide a continuous supply of larvae if adults do not stay and reproduce.
Green lacewings are usually sold as eggs, but also may be sent as larvae or
adults. Eggs are sent in a packing material to cushion and separate the emerging
larvae during shipment. The material — rice hulls, wheat bran, or corn grits,
along with moth eggs for food so the larvae will be less likely to eat each
other — also makes it easier to distribute the very tiny eggs evenly. The
lacewings should be released as soon as they begin to hatch. Releases are made
by sprinkling the contents of the container onto infested plants. The newly
hatched larvae will be very tiny (about the same size as the eggs) so you may
have difficulty seeing them. The released aphidlions will travel a considerable
distance, up to 100 feet, in search of prey. Making releases early in the
morning or late in the day when it is cooler, or on a cloudy day, increases the
chances the lacewings will survive. Larger larvae, which consume aphids at a
faster rate than newly hatched larvae, are available from some suppliers.
Because they are cannibalistic, lacewings purchased as large larvae must be
shipped in individual containers which increases the cost of the product.
Lacewings released as pre-fed adults that are ready to lay eggs can fly away
upon opening the shipping container, so greater care must be taken when
releasing lacewings at this stage to ensure their establishment in the infested
area.
The number of lacewings needed for effective
control depends on the pest population and climatic conditions. For control of
moderate aphid infestations in home gardens, 5-10 lacewing eggs per plant or
1,000 eggs per 200 square feet are recommended. Two or three successive releases
made at two week intervals are better than a single release. Suppliers usually
make recommendations based on specific situations. These insects are extremely
effective under certain conditions, especially in protected or enclosed areas
such as a greenhouse, but they may fail to survive and provide control when
conditions are not favorable.
– Susan Mahr, University
of Wisconsin - Madison
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