The bristly or tachinid fly is a parasitic fly that often feeds on common crop pests. These gray or brown flies lay their eggs on or inside caterpillars, beetles and other insects, or near the feeding areas of the hosts. When the eggs hatch, the maggots consume the bodies of their hosts and eventually kill them. These natural parasites often do their work unnoticed by the gardeners that they help. And these flies are not commercially available. However, there are over 1300 species of bristly fly located in virtually every corner of North America. It's relatively easy to encourage the bristly flies in your area to help you biologically control the pests in your garden.
Determine if the right species of bristly fly resides in your area. Certain species of bristly fly only feed on one species of insect, while most are indiscriminate feeders. Contact your local county extension office to enquire about the bristly fly activity in your area. Or, ask local farmers or land owners if they are aware of their presence. You may be able to take a few infected caterpillars (they will carry tachinid fly eggs on their heads or larvae in their bodies) or leaves home to your garden to jump-start your local population.
Use plants to attract bristly flies. Plants that attract bristly flies in large numbers include golden marguerite, buckwheat, lemon balm, pennyroyal, parsley, phacelia, tansy and crimson thyme. Locate these plants near the crops that are under seige, and soon you will have a thriving population of bristly flies.
Let your garden pests live for a season. Bristly fly eggs develop along with their insect hosts. If you kill the pests, you will also kill the bristly fly population and any hope of biological control. Once bristly flies are present, wait until the following spring when the bristly fly adults emerge, to see if your biological controls have done their job.