Pests Build Immunity to Poison

Insect pests fight their own kind of star wars against man’s efforts to drive them from farm and garden. Their great defense is building up resistance to the poisons.

One of the latest pest controls to lose some of its power is the renowned remedy against cabbage worms, Bacillus thuringensis, known as Bt.

This is a soil bacterium, a natural control embraced by gardeners for 30 years because of its touted harmlessness to humans and pets. But insects are now developing immunity, U.S. government researchers warn.

To deal with it, experimenters at the U.S. Grain Marketing Research Lab in Manhattan, Kan., are recommending a remedy that sounds easier for pros on the farm to work with than amateurs in the garden--rotation of Bt toxins, mixtures or sequences of toxins and varying the toxin dosage.

Current research projects reported by the U.S. Department of Agriculture indicate that cabbage loopers, corn ear worms, gypsy moth caterpillars and Mexican bean beetles are meeting their doom in another way.

Scientists have devised a means of attracting their devourers, spined soldier bugs, through a sex scent, or pheromone, enclosed in plastic doodads that look like badminton birds.

According to the U.S. Insect Chemical Ecology Lab in Beltsville, Md., one cone can attract 50 or more spined soldier bugs in one day, if it is put out one week before the bud-burst of the red maple tree from early March through mid-April.

The U.S. Agricultural Research Service replicated and patented the scent, which attracts soldier bugs of both sexes. Sterling International Inc., of Liberty Lake, Wash., obtained a license for the chemical blend and is marketing the cones under the name “Rescue.”

U.S. researchers are also experimenting with an environmentally friendly control for fruit flies in citrus by spraying the fruit with gibberellic acid, known as GA. The remedy could replace insecticides that might be banned by the Environmental Protection Agency.