Mayr and Darlington both suggested that the disease would probably take a larger toll of Harvard's elms if the trees were left unsprayed. But others argue that spraying is simply a desperate attempt to "do something" about a crisis when every other approach has failed.

The bark beetles emerge in April and sometimes fly large distances before burrowing into an clm to lay their eggs. Since the insecticides do not penetrate the bark of the elms, the argument goes, the beetles are essentially safe before they emerge from the winter and once they enter the new tree. This leaves only a few days for the insecticide to hit the adults before they lay their eggs.

Some experimenters have found the beetles unharmed after laboratory exposure to DDT. Others have gotten the opposite results.

"No amount of spraying will save the elm trees." Williams commented last month. "The only way of combatting the disease is to cut out the dead wood and cart it away."

The University has lost some two percent of its elms in the last 10 or 15 years, including five trees last year. Many of these trees were weakened by age and were easy targets for the Dutch elm disease.

Since no thoroughly effective control of the disease is in sight, B and G has replaced dead trees with oaks and other species of shade trees rather than risk losing more elms.

INSECTICIDES have created a particular problem for entomologists at the Bio Labs. When an organic phosphate insecticide was sprayed in the Laboratory's greenhouse last year, it drified into a ventilation fan and wiped out a colony of silk moths in another room. Ironically, these moths were part of a study on moth development and hormones-a project that may lead to a safer class of insecticides. (see box).

"In the old days, the watchman would see a cockroach running down the corridor, and he'd spray the whole place with DDT," Williams complained. "Of course I went right out through the ceiling. They can put you out of business overnight."

Williams's group has raised its moths in Medford during the summer toavoid pesticide fogs that may drift into the Bio Labs from nearby areas.

Before tree specialists stopped using hard pesticides like DDT to combat the elm disease, insecticide killings of birds were apparently common in Cambridge. Charles F. Walcott, a retired physician and amateur ornithologist, recalls seeing three insect-eating species-the robin, hermit thrush, and flicker-in "typical DDT convulsions" on his property off Sparks Street.

Several years ago, Matthew S. Meselson, professor of Biology, noticed robins in similar convulsions outside the Bio Labs after an insecticide spra?ing.

The long-term effects of pesticides on the ecology of Cambridge are much more difficult to isolate. The City has grown so rapidly in the past 60 years that changes in the local habitat could account for many shifts in animal? populations. For example, only 40 years ago, toads, raccoons and foxes ran around some of the city's vacant lots. Undergraduates in the nineteenth century reportedly shot woodcock-a small woodland gamebird-in the area between Harvard Square and the River.

Yet local wildlife experts have drawn two correlations of pesticide use and wildlife loss.

In 186? a French naturalist in Medford imported some gypsy moths for a breeding experiment. A few of the moths escaped, and the species had become ? severe pest by the turn of the century. The caterpillars completely defoliated Cambridge's trees, and most of Harvard's elms died, only to be replaced by more elms in 1915.

Carpenter recalls some areas around Boston "that sounded like rain from the excrement of the caterpillars."