If you're an aphid with a taste for tomato plants, the term 'biocontrol'
makes you quiver with fear. You'd rather not think about predators and
parasitoids with a voracious appetite for insect pests, especially since
their eating habits would qualify them for starring roles in an 'Aliens'
Biological control agents, a.k.a. "good bugs," are important parts
of integrated pest management (IPM) in the greenhouse. For them be effective,
growers have to monitor their crops frequently for the first sign of insect
pests. Once found, a pest must be quickly and accurately identified so
appropriate biocontrol species can be purchased while the pest population
is still low. If the pest population becomes high, then biocontrols rarely
provide satisfactory control because they can't reproduce as fast as the
more numerous pests unless one is willing to pour a lot of money into
the task. Before and after introducing a biocontrol, pesticides must be
avoided or carefully selected so that good bugs aren't killed along with
There are several dozen species of commercially available biocontrols
for a wide range of pests, and just a few examples are listed below. Don't be
put off by the Latin species names of these good bugs, they'll still work
fine even if you can't pronounce their names!
Aphidius of several species are tiny wasps that inject their eggs
into the bodies of immature aphids (the nymphs). Aphidius wasps are parasitoids,
meaning they reside in their host and eventually kill them. In this case,
a wasp hatches inside an aphid and, as it grows, it consumes the aphid's
innards. When the food is gone, the wasp cuts a neat exit hole in the backside
of the host and emerges, leaving behind a hollow aphid shell, or 'mummy.'
Your friendly biocontrol distributor can help you select the species of
Aphidius that will work best on the type of aphid pest you may have.
Aphidoletes aphidimyza is a midge that looks like a tiny mosquito.
In the immature stage, this guy is a predator, meaning it hunts and consumes
prey. The adults fly at night, locate colonies of aphids, and lay their
eggs nearby. The eggs soon hatch into fast-moving orange larvae with a
hankering for aphid meat. They run after the aphids, bite them on the knees,
and inject them with a paralyzing toxin. Then, they literally suck their
guts out. On a good day, a single A. aphidimyza larvae can chow down on
50 aphid Slurpies. They eat most all flavors of aphids, except melon aphids.
Many ladybugs are also predators. In the greenhouse, the convergent
ladybeetle, Hippodamia convergens, feeds on aphids and spider mites. Ladybugs
do not always provide successful, long-term control but they are useful
to "knock down" an infestation. These predators are collected in the wild,
but availability is good, except during the early summer months when supplies
may be sold out. Ladybugs can be stored in the refrigerator for several
weeks and released one handful at a time. They are usually thirsty when
released, so plants should be misted prior to release. Releasing them in
the evening is also important.
Encarsia formosa is a tiny parasitoid wasp used to control greenhouse
whitefly. It lays its eggs inside whitefly larvae, which young wasps later
consume and kill. Encarsia formosa comes to the grower as parasitized whitefly
pupae stuck to small cards. The cards are easy to hang on plants below
the canopy, out of direct sunlight. The wasps do best when daytime temperatures
exceed 72 degrees and nights are above about 60 degrees. At lower temperatures,
and at low light levels, the whiteflies reproduce too fast for Encarsia
formosa to control them.
Phytoseiulus persimilis is a predatory mite for control of two-spotted
spider mite. This is a case of a fast mite that can run down and eat slower
mites. The predator is shipped mixed with vermiculite or bran and must
be released carefully by sprinkling a little on every infested leaf. It
becomes established in the crop in about one week. Predatory mites prefer
moderate temperatures and humid conditions (60 to 90% relative humidity).
Spider mite populations have a tendency to explode when it gets hot and
dry, so early or preventative releases of Phytoseiulus persimilis are key
Steinernema species and Heterorhabditis species are parasitic nematodes
that attack a variety of soil dwelling insect pests. These include the
larvae, or grubs, of certain beetles, and weevils. The nematodes enter
the pest larvae then they multiply inside their bodies, killing them and
then leaving by the thousands, seeking out other susceptible larvae. A
moist soil environment is a requirement for success with parasitic nematodes.
The nematodes can be supplied in a spray concentrate or a moist granular
carrier. Some growers apply them using injector systems or diluting them
with water and using a pump sprayer, hose end sprayer, watering can or
Biocontrols can help reduce or eliminate insecticide use in the greenhouse.
And although they can be more expensive than chemicals and don't work as
fast, they're a lot more fun to use! Biocontrols have been growing in popularity
over the past few years as prices come down and growers learn how to use
them effectively. This one case where biological warfare is good thing,
although aphids may beg to differ.
Sources of biocontrols include:
9664 Tanqueray Ct.
Redding CA 96003
IPM Laboratories, Inc.
Locke NY 13092
Koppert Biological Systems, Inc.
28465 Beverly Rd.
Romulus MI 48174