Diet seems to affect the resistance of the flies to insecticides. Flies fed a rich protein-vitamin diet can resist even the most toxic materials. Flies fed an ordinary fruit pulp-sugar-water diet showed 66 percent mortality after 48 hours of exposure to parathion, 1 part to 200,000 parts of water, but only 1 percent of the protein-fed flies died.

Some insecticides are more toxic than others to the fruit fly parasites. This is significant in Hawaii, where the beneficial insects are so important, and would require similar consideration if it ever becomes necessary to try to establish the parasites on the mainland.

Lures have been developed that will attract the male fly for long distances. One of them is a clear liquid, methyl eugenol. More than 1 million male flies were caught in 45 traps from July to September, 1950. Some of them were attracted to the lure from a distance of a half mile. Use of the lure, poisoned with parathion, is an effective way to rid an area of the male flies.

The female fly is attracted to fermenting baits, such as a sugar-yeast combination. New lures six times more effective than the old standard lure have been developed, first from protein hydrolysate and later by using vitamin B complex. The next step is to test the constituents of the complex to increase further its effectiveness if possible and to reduce costs. An effective eradication program or an orchard spray program, in the event the fly ever becomes permanently established, would benefit immeasurably from lures that could be added to poison sprays.

THE AREA-CONTROL PROJECT is closely related to chemical control. Area control theoretically would best follow a well-developed chemical control, but delay could not be permitted if large-scale control methods were to be available for early mainland use. Area control has only one purpose to develop techniques and methods whereby an incipient infestation could be contained and eradicated.

In Hawaii, it is possible to develop techniques and methods only because no attempt at eradication is feasible. Even an operation covering a whole island would not eradicate the fly, because of its ability to travel long distances.

Data on fly movement have been obtained by releasing and later trapping marked flies. A spot of color was dabbed on the thorax of flies, which had been chilled to permit easy handling. Marked male flies have been recovered 20 miles from their point of liberation. Flies have crossed an ocean strait 9 miles wide. They evidently move back and forth over each island and possibly over more than one island. They can be carried on the outside of fast-moving vehicles for great distances. Such mobility would complicate quarantine and control measures should an infestation occur on the mainland.

AEROSOL SPRAYING would be an ideal method for controlling the insect in urban areas, which in Hawaii are rich in host fruits. Tests with light doses of DDT applied in this way have been promising, having reduced adult fly populations by 98 percent. The tests were made in villages on the windward side of Oahu, which are relatively free from reinfestation, each entire village being used as a sample control area.

The first step taken in area control was to determine the various types of areas, since control would differ, depending on whether the area was purely urban with fruit fly hosts in home gardens, or urban with wild hosts nearby, or extensive wild-host areas. After 18 months of intensive study of type areas, it was decided to increase the size of field experiments so that they would serve as control-demonstration plots.

Control operations over the wild-host areas, which are mostly covered with guavas, have had to be by airplane. Here again, the habits of the fly have complicated the technique. Airplane application deposits most of the insecticide on the upper surfaces of the leaves; the fly spends most of its time on the lower surfaces. Addition of sugar to a DDT emulsion resulted in bringing the flies to the top surfaces of the leaves and greatly increased control.

Lanai Island is well suited for area control. It has approximately 89,000 acres, including a low, tree-covered mountain range, a town full of host trees, large areas devoted to pineapple plantings, and almost-desert slopes. The movements of the flies have been followed carefully. The host fruits, wild and cultivated, have been mapped and their seasonal sequences plotted. Wild-host areas, principally guava on the lower mountain slopes, have been aerially surveyed to determine the feasibility of defoliation techniques that will eliminate the current crop of fruits. Guava areas on the island have been divided into three plots of approximately 500 acres each to provide three separate experiments. Guavas elsewhere were too scattered for effective spraying, and were either temporarily grubbed out or treated with a defoliant spray to knock off the current crop.

The central town of Lanai was also divided for experimental purposes. One-half was treated with a fog sprayer, and the other with dilute spray. Strict sanitation was practiced, and all fallen fruit collected and disposed of.

Two other small and isolated areas on the island were used for some other experiments. Subject only to limitations imposed by weather, the operations proceeded at the same time so that actually a huge control program, organized on an experimental basis, was under way. Upon completion of the actual operations, studies to evaluate the results were conducted for several months.

ONE MAJOR SOURCE of loss that can result from infestation is the embargo that must be placed promptly on the movement of commodities out of an area infested with fruit flies. Hawaiian agriculture has experienced many of these embargoes.

The effect of an incipient infestation on the economy of a large fruit-growing area in California, if shipments out of the area were suddenly stopped, would not be difficult to visualize. Authorities in California have been so alarmed at the prospect that a staff of investigators has started work on the problem in that State.

The immediate answer is the development of commodity treatments. They can be studied only in Hawaii, where infested fruits can be used. The limiting factor in the rapid development of treatments is the fact that a treatment that will kill the pest is likely to damage the commodity. Therefore two aspects must be studied. One is the effect of the treatment on the insect eggs and larvae, and the other the tolerance of the commodity to the treatment.

Tolerance varies greatly between different fruits. The tolerance of the huge list of California fruits cannot be judged by the way tropical fruits in Hawaii react. The California staff, therefore, is testing the tolerance of those fruits to treatments developed in Hawaii.

The procedure to be followed before any particular fruit or vegetable can be shipped from Hawaii is exacting. First, it must be effective. In fact, treatments which have been permitted are usually more severe than the statistical chances of infestation would seem to make necessary. Second, it must be practical so as not to impose too great a burden or expense on the shipper. Third, it must leave no harmful or objectionable residue on the fruit.

Vapor-heat treatment, the most widely used, consists of heating the fruit for 8 3/4 hours at 110 F. in a saturated atmosphere. Some fruits require a period of heating at somewhat lower temperatures and at reduced humidity in order to tolerate the long period at 110 , so that the entire process takes more than 16 hours. Therefore it is not deemed the most practical method for treating large quantities of fruits, especially as it requires specially designed rooms and equipment. In Hawaii the vapor-heat method has been approved for papayas, zucchini, bell peppers, pineapples, and tomatoes.

FUMIGATION with toxic gases offers the best solution for large-scale operation because, with a suitable gas, freight cars could be treated and sealed off so that part of the treatment could actually take place en route and involve a minimum of interference with commerce.

Methyl bromide can be used to fumigate the fresh fruits and vegetables that will tolerate it. The standard dose is 2 pounds of the fumigant for each 1,000 cubic feet of space. Many commodities will not tolerate methyl bromide. In Hawaii it has been used only for fresh pineapples.

New fumigants are being sought. Two other bromine compounds, ethylene dibromide and ethylene chlorobromide, may soon be available as permitted fumigants. They are so toxic to fruit fly larvae and eggs that greatly reduced dosages can be used. This lowers the hazard of injury to the fruits.

Hundreds of other compounds are being tested for their toxicity to eggs and larvae. As rapidly as the tests are completed, the data are sent on to the California workers for inclusion in their tolerance tests.

Low temperature is a third possible method of treatment. These tests take longer than others, because of the prolonged development time for the insect at low temperatures. The results, however, are gradually accumulating and offer promise for some commodities which are normally stored at low temperature.

The, index of infestation is determined by making systematic collections of fruits and vegetables in the field, holding them in specially designed boxes, and recording the average number of flies emerging from each host.

Theoretically the severity of infestation in commodities for export determines the degree of treatment, but a valid procedure for determining incidence of infestation is difficult to achieve. In actual practice, commodity treatments are determined on such an extreme safety factor that the indexes of infestation up to now have not really functioned in establishing these treatments. One example illustrates the difficulties. A year's collection of papaya for index-of-infestation purposes showed one larva in about 4,000 mature green papayas, which is the stage used for commercial shipping. From a recent collection, however, a single mature green fruit yielded 68 oriental fruit fly pupae. With the tremendous reduction in populations of the fly now being recorded, however, it should be possible to make practical use of the index in establishing treatment levels.

WALTER CARTER is a graduate of Montana State College and holds advanced degrees from the University of Minnesota. After 5 years with the Bureau of Entomology and Plant Quarantine, in charge of entomological work on beet leafhopper, he joined the staff of the Pineapple Research Institute of Hawaii as the head of its entomology department in 1930. Since then he has had wide experience with tropical entomology, including membership in an international commission to the Gold Coast of West Africa. In 1949 his services were made available to the Bureau of Entomology and Plant by Quarantine by the Pineapple Research Institute to organize and direct the research ova fruit fly. He returned to full-time duty with the Institute on July 1, 1951.