Scientists with the Agricultural Research Service have come up with the first synthetic diet that supports rearing the Colorado potato beetle from egg to adult--without the potato plant. This beetle is the potato crop's most destructive pest.

Normally, the beetle is in abundant supply for such tests only from May to July. But the new diet lets researchers rear the beetles in a laboratory at any time to test potential new controls such as natural compounds from plants. For example, they found that adding high levels of tomatine--a compound in tomato leaves--hinders the beetle's growth.

The Colorado potato beetle feeds on leaves of potato along with its plant relatives eggplant and tomato. Growers frequently apply insecticides to control the critter, but it has armed itself with resistance to many chemicals.

Researchers at ARS' Beltsville (Md.) Agricultural Research Center set out to develop a diet without plant material. That's because the different types and levels of substances present in plant leaves can skew test results. The new diet uses no potato foliage or extract. It has a gelatin-like consistency and is cut into tiny cubes and served to the bugs.

ARS scientists based the formula on a chemical analysis of the nutrients in potato leaves. This gives the artificial diet uniformity--and is the reason researchers could use it to evaluate potential control agents such as the tomatine compound.

Scientific contact: John M. Domek, ARS Insect Biocontrol Laboratory, Beltsville, Md., phone (301) 504-5689, fax (301) 504-5104.