Forum -- Biosystematics: Putting Pests in
It's easy to summarize the goal of biological control: to foil the pest
without fouling the environment.
But to accomplish this goal, we must have a thorough understanding of the
crop pest. We must know our enemiesand, in turn, know their
enemiesso that we can find a way to put the latter to work for us.
This approach calls on the science of biosystematics to understand, say,
where a specific insect fits into the bigger picture in nature. If we can make
an accurate connection between a particular insect and related insects, we
obtain a solid foundation of collective knowledge from which to predict how the
newcomer will behave.
We then have a head start on pinpointing this new insect's enemies or
finding ways to use it to control other insects.
For example, if we know a targeted crop pest originated in the Mediterranean
region, we know where to search for its natural enemies. Or if we can predict
an insect's life cycle, we can make a smart guess about where to search for it.
And if we know that one member of a group of wasps is effective against a
crop-damaging beetle or worm, then we can look for other helpful members in
that same group.
Effective biological control of crop pests depends completely on making
these types of connections. When we take advantage of a systematic view of
accumulated knowledge, we don't have to start from scratch with each new pest.
Fortunately, scientific toolssuch as the ability to compare insects'
DNAare simplifying our search for the relationships between different
insects, so we can more quickly increase our arsenal of natural weapons against
One concern about biological control agents is the element of riskthe
fear that once a beneficial insect has been introduced into a new environment
and eliminated its target pest, it will turn to other sources of food, such as
a crop or other desirable plants.
Happily, nature has provided us with a valuable safeguard: There are host
range limits beyond which an insect will not go. So if we use a predatory
insect that's always feasted on tomato worm larvae, it's not going to suddenly
switch to a diet of tomatoes. An insect with mouth parts evolved for sucking
can't promptly switch to chomping.
In fact, there's a complicated hierarchy of events that must occur for a
parasite or predator to go after even the pest it has evolved to attack. If the
parasite can't identify the habitat that the pest is in or find the plant where
the pest is lurkingor if it dislikes that particular life stage of the
pestit's all over; the parasite doesn't do anything.
A growing knowledge of that type of specificity helps speed our selection of
beneficial organisms and avoid undertaking research on predators or parasites
that might attack nontarget species.
Still, we don't rely blindly on existing knowledge to protect us against
possible good-guys-turned-bad bugs. Potential biocontrol agents are studied
extensively in quarantine before their release into the environment.
For example, if an insect will be used to control a weed, we might put it in
a greenhouse with a large variety of selected plants to see if it attacks
anything other than the target weed. To the extent that we understand the weed
systematics, we can make intelligent choices on the plants to test.
Our job is to try to protect crops, rangeland, and livestock from pests.
There was a time when we mainly used insecticides that simply killed all the
insects out therebeneficial or otherwise. We've learned from past
experience that's not going to work.
As we move away from a scattershot approach, we need more specific ways to
control pests. To the extent we understand where a particular pest fits in the
world, we can devise specific means for managing it. Our understanding of this
specificity begins with biosystematics.
James L. Krysan
Former ARS National Program Leader
for Pest Management Systems