Ask those fly predators to stick around! 

Strategies for Encouraging
Beneficial Insects in the Field

FIRST POSTED:  October 2001
RELATED ARTICLE:  Managing filth flies with parasitic wasps

By Dr. Richard McDonald

Imagine you’ve just received an invitation in the mail to attend a banquet being held in your honor.  The menu accompanying the invitation lists all your favorite foods.  Are you going to come?  You bet you are!!

The gist of this analogy is that just like us, beneficial insects need sources of food and shelter in order to stick around.  You can weave “web of life” in your garden or farm by planting specific plants.  Also, by thinking ahead and anticipating the types of pest problems you might have, you can encourage the right beneficial insects to be there when you need them to attack the pests.  My motto is: “If you plant it, they will come. Or, I will buy them (beneficials) once and have them here forever after...”

In fact, in keeping with this perspective, think of two terms: 

These two comparisons are equal to the difference between Eastern and Western medical thought--Western medicine treats the illness or its symptoms, while Eastern medicine, with its use of tonics, focuses on keeping you well in the first place.  It is the same with your garden or farm.  By using IPPM and having the beneficials there IN THE FIRST PLACE, you can nip  many of your pest problems in the bud before they ever have a chance to become a problem.

So let’s look at a few ecological principals to make your garden/growing area more attractive to beneficial insects:

1) Have something blooming all the time - This may be impractical in the winter months, but if you have a greenhouse, let some of your crops bloom.  For example, crucifers like broccoli have flowers that are very appealing to beneficial wasps.  It also turns out that these flowers are prime mating sites for the wasps, too. This is good news, because if a female wasp is not mated, she lays all male eggs, the population crashes, and so does your beneficial wasp population. Also, if you have a greenhouse, you can “jump start” your beneficial insect populations there, and then let them out into the garden or farm to welcome the pests as they arrive.  

2)  Nectar - Many beneficials, from parasitic wasps to ladybugs, need to have nectar around.  Some of the best plants you can have for this purpose are those in the wild carrot family (also known as Umbellifera), such as dill, fennel, tansy, queen Anne’s lace, caraway, coriander, parsnip, etc.  Also, other plants have “extrafloral nectaries,” or nectar glands that are not associated with flowers.  

A good example of this is the peony or sweet potatoes.  Peonies have extrafloral nectaries located on their leaves, which is why they are usually covered with ants, who are guarding and hoarding the nectaries for themselves against other insects.  Sweet potato plants have these extrafloral nectaries too. Parasitic wasps and parasitic flies use these extrafloral nectaries as important food sources.

For fly parasites, their favorite food plants are in the wild carrot family (Umbellifera).  By planting a variety of these types of plants – dill, fennel, Queen Anne’s Lace, Patrinia, Tansy, Coriander, etc., near your fly breeding areas (along fences or other out of the way places), you can ensure that some of these plants are in bloom during the seasons you need them - which with flies is nearly year round.  Make sure your fly parasite wasps are getting their minimum daily adult requirement of nectar.  Studies have shown that wasps well fed by nectar lay 3-fold to 5-fold more eggs than “normal” wasps.

3) Pollen - When certain predatory insects (which beneficials often are) have eaten almost all of their prey population, they will leave unless there is an alternative form of protein around.  Once again, many plants in the wild carrot family can provide pollen. Another good pollen producer is the corn plant, with its big tassle on top showering everything around it with pollen.  In fact, many fruit farmers in California are now planting corn in their orchards to keep the beneficials there.

4) Overwintering sites for beneficials - It turns out that many beneficials make cocoons and hibernate in or very near the plants where they find their hosts.  For example, let’s take broccoli again.  By leaving some broccoli plants to overwinter, the cocoons of parasitic wasps can survive on the plant, and then become the starter colonies of beneficials to ride herd on the first pests that attack broccoli, like the imported cabbage worm, Pieris rapae (L.). It might look a little messy to leave the plants in the field and not compost them, but, hey, who says pest management comes without a price? If this strategy is not to your liking, another would be to pull the broccoli plants up and set them aside somewhere (until mid- to late-April or so) in order to make sure that the beneficials have emerged, before you compost the plants.  Recent research has shown that yarrow and comfrey are also excellent overwintering plants for parasitic wasps.

Finally,

5) Encourage Biodiversity!  - Remember that insects are part of the web of life in your garden or farm (or compost facility). The beneficial insect complex is not only composed of parasitic wasps and flies, predatory beetles, lacewing larvae, ladybugs and so on, but ALSO the pollinators, antagonists/competitors that occupy and compete for space and food with potential pests, and finally the saprophytes and decomposing insects that help complete the food cycle back to the soil so the cycle can start again.  And remember, “if you plant it, they will come....” 

For further information on Farmscaping, go to the ATTRA web site (www.attra.org) and click on the publications section.

I welcome letters/inquiries/comments sent to me at the following addresses:
Symbiont Biological  Pest Control, 194 Shull’s Hollar, Sugar Grove NC 28679
(828) 297-BUUG or email: the_edge@boone.net
www.drmcbug.com

FARMSCAPING: Top Fall Appalachian Plants for Beneficials

Patrina, Autumn joy sedum, vetches, chrysanthemum (Pacifica), tansy, bronze fennel, garlic chives, yarrow, Comfrey,  and some of the last broccoli for overwintering on/underneath, Queen Anne’s Lace/other wild carrot family plants, Goldenrod