Frank M. Carpenter, Fisher Professor of Natural History, discovered evidence that might support this theory. He simply noticed that the unsprayed ivy on the Shannon Hall side of the Bio Labs was much less moth-eaten than the sprayed ivy on the Divinity Avenue side of the building.

A group of biologists including Carpenter, Mayr, and Philip J. Darlington, Jr., Alexander Agassiz Professor of Zoology, urged B and G to stop spraying the ivy long enough to allow the moth's natural predators and parasites to return.

In 1965 B and G halted all ivy spraying on seven buildings north of the Yard. None of these have been sprayed since, but B and G will apply some 20 gallons of meta-systox-R, an organic phosphate insecticide, to the ivy in the Yard and elsewhere next month.

This chemical is called a systemic insecticide because it permeates the entire ivy plant, making the whole plant-not just its surface-poisonous to insects.

For two years after the spraying stopped north of the Yard, the caterpillar population skyrocketed.

Many old ivy plants, weakened by a severe drought, failed to survive despite special feeding and watering treatments. It may take a decade to replace the lost ivy.

But the moth's enemies, including a parasitic wasp that lays its eggs on the caterpillars, have apparently staged a comeback. And many biologists suspect that the new ivy around the Bio Labs is less moth-eaten than the sprayed ivy in the Yard and Business School areas.

If the ivy moth population remains in check this year, the biologists may suggest a de-escalation of the ivy moth war elsewhere in the University.

However, the ivy caterpillar population has the nasty habit of peaking in June-just about the time when the old grad population peaks in the Yard. A year or two without spraying there could defoliate the ivy for several Commencements.

A state entomologist at the Shade Tree Laboratory Field Station in Waltham suggested that a commercial preparation of the bacterium Bacillus thuringiensis might keep the moth population down for several years while the natural predators re-establish themselves. This particular biological control has recently halted the cabbage looper and fruit cankerworm, but it has not been tried against the ivy moth.

After five seasons of reduced ivy spraying, the biologists believe that the moths and parasites have struck an equilibrium. But "we haven't put in a recommendation yet because we have only had one good summer," Darlington said. "We need one more good summer before we know where we really stand."

ASMALLER number of biologists have also taken exception to the University's spraying program for the Dutch elm disease-a fungus infection imported from Europe. Two species of bark beetle known as Scolytus multistriatus and Hylurgopinus rufipes, inadvertently carry the fungal spores that cause the disease. B and G tries to control the beetles by spraying Harvard's clms in early April before the insects emerge from hibernation.

This year, a B and G contractor sprayed 90 gallons of methoxychlor, a chlorinated hydrocarbon that does not accumulate in the natural food chain as its close relative, DDT, does.

Later in the summer, a contractor also sprays for the clm leaf beetle, Galerucella xanthomelaena. This beetle does not spread the elm disease itself, but large infestations of these insects may weaken the elms and reduce their resistance to the fungus.

It is not quite clear whether spraying actually controls Dutch clm disease. Government studies indicate that spraying does reduce the disease on well-controlled experimental plots, but whether spraying is effective under field conditions is still open to debate. Some communities simply remove the dead wood that the beetles breed in, and they claim to have good disease control without spraying.