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Green Laceings:
Are These Upaid Workers In Your Cotton? |
5
These green lacewings are common in much of North America.
Adults feed only on nectar, pollen, and aphid honeydew,
but their larvae are active predators. Adult green lacewings
are pale green, about 12-20 mm long, with long antennae
and bright, golden eyes. They have large, transparent, pale
green wings and a delicate body.
Adults are active fliers, particularly during
the evening and night and have a characteristic, fluttering
flight. Oval shaped eggs are laid singly at the end of long
silken stalks and are pale green, turning gray in several
days. The larvae, which are very active, are gray or brownish
and alligator-like with well-developed legs and large pincers
with which they suck the body fluids from prey.
Prey
Cotton, sweet corn, potatoes, cole crops, tomatoes,
peppers, eggplants, asparagus, leafy greens, apples, strawberries,
and other crops infested by aphids. Several species of aphids,
spider mites (especially red mites), thrips, whiteflies,
eggs of leafhoppers, moths, and leafminers, small caterpillars,
beetle larvae, and the tobacco budworm are reported prey.
Life Cycle
Green lacewings overwinter as adults, usually in leaf litter
at the edge of fields. During the spring and summer, females
lay several hundred small (<1 mm) eggs on leaves or twigs
in the vicinity of prey. Larvae emerge in 3-6 days.
The larval stage has three instars and lasts
two to three weeks. Mature third instars spin round, parchment-like,
silken cocoons usually in hidden places on plants. Emergence
of the adults occurs in 10 to 14 days. The life cycle (under
4 weeks in summer conditions) is heavily influenced by temperature.
There may be two to several generations per year. These
lacewing larvae are considered generalist beneficials but
are best known as aphid predators. The larvae are sometimes
called aphid lions, and have been reported to eat between
100 and 600 aphids each, although they may have difficulty
finding prey in crops with hairy or sticky leaves.
Habitats
Mass releases of C. carnea in a Texas cotton field
trial reduced bollworm infestation by 96%, although more
recent studies show that C. carnea predation on other predators
can disrupt cotton aphid control. C. carnea is considered
an important aphid predator in Russian and Egyptian cotton
crops, German sugar beets, and European vineyards. Adult
lacewings need nectar or honeydew as food before egg laying
and they also feed on pollen. .
Therefore, plantings should include flowering plants, and
a low level of aphids should be tolerated. Artificial foods
and honeydew substitutes are available commercially and
have been used to enhance the number and activity of adult
lacewings
Dispersal
These products may provide sufficient nutrients to promote
egg laying, but they cannot counter the dispersal behavior
of newly emerged adult lacewings. These beneficial insects
are shipped as eggs, young larvae, pupae, and adults. Larvae
are likely to remain near the release site if aphids or
other prey are available. Newly emerging adults, however,
will disperse in search of food, often over great distances,
before laying eggs.
SCP has made green lacewing releases in most
all the project fields. They are available commercially
and our field scouts can provide you with contact information
if you would like to purchase additional larva for release
in your cotton or other crops.
Why
Is Biological Control Important?
Issues such as high chemical costs, pesticide resistance,
environmental degradation, and water and worker safety have
promoted researchers, growers, and policy makers to pursue
alternative strategies to pest management. Biological control
has emerged as one of the more successful, safe and sustainable
strategies.
Experience at Work
Much of the information for this article is taken from the
lifetime of experiences of Deke Dietrick, Board Certified
Entomologist of the Dietrick Institute. Deke has been active
in the biological control movement since 1955, and may be
one of the first pest control advisors to market advice
on biological control. In his work in the Coachella Valley,
he learned that natural biological control was possible
in cotton and that optimum yields and quality were produced
using no pesticides. This article will discuss some of the
basics of biological control in cotton which can be utilized
to your economic advantage.
Natural Balances
Predators and parasites can often prevent a pest
population from reaching treatable levels, and the control
they provide is often cheaper, better, and longer lasting
than that provided by insecticides. Scouts and growers should
be aware of population levels of naturally occurring predators
and parasites and should recognize that biological control
can bring about a natural balance with out the use of expensive
chemicals.
In Search of Food
Deke discovered in the decade of the fifties, that food
drives all of the interactions of over one thousand species
of potential plant feeding pests, predators, and parasites
as well as all of the naturals processes affecting these
insects including diseases and decomposition. Along with
other researchers, he found cotton gown adjacent to alfalfa
had a wider range and diversity of insect species. The insect
pest Lygus develops in large numbers in alfalfa and then
often moves in huge numbers into cotton when the alfalfa
is mowed. Much work has been done to help show that strip
mowing of alfalfa might prevent large scale migrations of
lygus and thereby reduce the threat to cotton. When the
entire alfalfa field is mowed all at once, a dense and lush
plant cover is eliminated, leaving many arthropods without
food and shelter and exposed to high temperatures and high
humidity. Work as early as the 1960’s showed that
strip harvested fields prevent this mass migration and thus
reduced damage in cotton.
Creating Balance
By developing a set of practices that includes strip cutting
of alfalfa, habitat planting and enhancement, regular monitoring
and proper pest identification, growers are well on their
way to biological control. Pest identification is an important
consideration in control of cotton insects, and before making
control decisions, growers must correctly identify the pests
or pest complex. This requires detailed study in pest characteristics
and the type of damage associated with each pest species.
It is also essential that you develop a regular
monitoring program that permits reasonably accurate population
estimates of not just the pests, but beneficials as well.
Cotton "scouting" involves taking systematic data
on pests, beneficials, and plant characteristics from each
field. Deke and his colleagues invented vacuum insect sampling
equipment to monitor all of the insects and mites found
in cotton and its adjacent alfalfa. Sampling each week of
the growing season, they observed the full impact of biological
control. Says Deke, “We found that this diversity
of migrating and resident insects and related organisms
vacuumed from the plants provided sure, dependable resources
that protected the cotton from predicted disasters. Producing
top yields and quality cotton was free to those who would
farm with this natural biological control.”
Biological control should be encouraged and
enhanced by adding additional food for insect populations.
This is best done by having adjacent plants with lots of
blossoms and encouraging all species of predators through
habitat enhancement planting and mulches.
The avoidance of pesticides, reducing excessive
road dust, and border plantings of Sudan grass, sunflowers,
corn, sorghum are examples of how biological management
practices can protect insect predators and help avoid damaging
pest outbreaks.
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