To each pest, a predator

Walking around the garden in late summer means you’ll typically be assaulted by a number of undesirable crawlies. Whether or not you know much about bugs, you undoubtedly know these guys: Asian tiger mosquitoes that flit away quickly after snacking on your ankle. Japanese beetles mowing down your prize rose bushes while brown marmorated stink bugs busy themselves with wrecking barely ripe tomatoes.

These are just a few of the most recognizable members of an ill-famed club: non-native invasive insects.

They make the news each year with stories of death and destruction, like the emerald ash borer causing the rapid decline of ash trees across the country, gypsy moths defoliating large swaths oak and aspen, or hemlock wooly adelgid steadily wiping out one of our stateliest native conifers. Conventional chemical sprays have little long-term effect on many of these introduced insect species, and they have continued to prove themselves difficult, if not impossible, to control.

You might think that stink bugs are only a recently introduced phenomenon from abroad, but the truth is that there are American stink bugs, too. Some native stink bugs are actually beneficial predators! But others cause problems just like their marmorated cousins.

The difference with native pest species is that they have been confined on this continent with a corresponding predator for many thousands of years. In that time, a delicate balance developed between predator and prey, and though pests will be pests, their natural enemies do a good job of keeping populations in check.

This equilibrium is the result of coevolution, a term coined in the 1970s by ecologist husband-and-wife team Anne and Paul Ehrlich. It applies to many different relationships: those between pollinators and flowers, caterpillars and their food plants, predator and prey.

Introduced species, on the other hand, arrive here without their counterbalancing predator, with the result that the pests proceed to run rampant. They’re literally like kids in a candy store without a chaperon.

Researchers continue to look into how native predatory and parasitizing insects might be persuaded to develop a taste for foreign invaders, or whether it is safe to bring non-native predators in to eat their ancestral prey. Tiny, non-stinging parasitic wasps and flies are among the most common natural enemies for a wide range of insect pests, and are being looked at as possible controls for many of the most damaging non-native pests that have come here in recent decades.

Specifically with the brown marmorated stink bug, researchers hope that a one-two punch will be an effective strategy to control stink bug populations. U.S. Department of Agriculture researchers are looking at releasing a tiny Asian wasp (Trissolcus japonicus), which is the usual control on the stink bug in its home region, to help a U.S. native parasitic wasp (Telenomus podisi) that also parasitizes stink bug egg masses. Together, these two wasps could very well keep stink bug from causing so much trouble.

People are understandably leery of bringing in yet another non-native species to deal with a non-native problem. The USDA’s Beneficial Insects Research lab in Delaware regularly imports, quarantines, researches and releases non-native predators and parasites in an effort to deal with introduced pests without chemicals, and works to reassure the public that these “solutions” don’t become problems themselves.

The alfalfa weevil


One success story is that of the alfalfa weevil, which was once a major pest of northeastern alfalfa crops but is now managed by a range of USDA-introduced parasites. The savings to farmers rings up to an eye-watering annual average of $88 million in control costs.

So next time you see a stink bug, take heart: the day may not be far away that they won’t be teeming by the thousands in your rafters and sock drawers, all without a drop of pesticide.

Article by Michelle Donahue, FCFCDB member

Nature Note for 8/31/14