Better Weapons for Battling Bugs

Though it once seemed impossible, the snow has finally left our gardens. The mud is drying, the plants are growing, and so are the insects that aim to eat our vegetables before we do.

With good seasonal timing, Science magazine has just printed an article to stir hope in gardeners who are not looking forward to the summer-long battle with the bugs. The subject is an unusual term likely to become very familiar over the next few years: biopesticides.

Biological pest control agents are not new, in either human experience or the natural world. Alaskans, for example, repel mosquitoes by burning products having an active ingredient--pyrethrin--obtained from pyrethrum daisies. And just as there are germs and parasites that make people sick, so too are there germs and parasites that make insects sick. The trick has been to find and tame them.

The first modern biopesticide was employed about forty years ago, when researchers found a bacterial disease that killed the tree-destroying caterpillars of the gypsy moth. Bacillus thuringiensis produces spores that release toxic proteins when eaten by insect larvae. A mixture of the spores and the toxic protein crystals sprayed on tree foliage kept leaves from being eaten and decimated gypsy moth populations, and unlike artificial chemical poisons, didn't kill desirable insects like butterflies and honeybees. B. thuringiensis, known as Bt for short, has many subspecies, and each bacterial breed attacks only a narrow range of insects within one order.

This specificity is both good and bad; from an environmental point of view, it's good, because the innocent are not slain with the guilty bugs. From an economic point of view, it's not so good. Commercial producers of the bacteria would have to breed many different kinds to have products to kill cucumber beetles as well as gypsy moths. Customers might not buy twelve varieties of biopesticide when one artificial compound can kill all twelve pests.

Now genetic engineering has entered the picture. First, scientists working at the University of Washington and in Britain found that the Bt poison was chemically consistent among the bacterial strains, but that its ability to bind to the body chemistry of an insect was not. Tinkering with the bacterium's genetic code then produced broader binding domains; the engineered strains can affect more kinds of insect pests while not harming other creatures.

The next steps are only a bit more experimental. Genetic engineering techniques permit taking the Bt genes responsible for producing toxins lethal to certain insects and inserting them into other kinds of bacteria. Researchers at several laboratories have pulled off this trick with bacteria that naturally live within corn plants but don't harm the plants. The corn plants containing the altered bacteria are receiving a continuous supply of natural insecticide, harmless to mammals, birds, and just about everything else except corn borers. For them, each nibble comes salted with deadly poison.

The most ambitious of the genetic engineers have introduced Bt toxin-producing genes directly into the hereditary material of specific plants. Field trials conducted last year with cotton plants containing working Bt genes showed they were as protected from bollworm damage as were neighboring plants sprayed regularly with strong insecticides.

All this is from just one bacterial species, and there are many other promising bacteria, fungi, and viruses. Biological controls seem to combine the best of both organic methods and chemical pesticides. They are natural; they don't build up in the food chain; they don't harm humans who apply them or who eat them. These toxins kill, but they kill only the target pests.

Built-in or sprayed-on biopesticides aren't yet available for Alaska's gardens, but they're coming. Before the turn of the century, we should be able to grow vegetables that won't need chemical spraying to win the battle of the bugs.