The publicity that surrounds Medfly eradication programs seems to generate all sorts of "experts."
One group says that the Mediterranean fruit fly cannot, over time, survive the California climate--it is either too hot or too cold. This contention flies in the face of facts. We have collected live larvae from fruit in the middle of winter in Northern California and in the middle of summer in Southern California. Moreover, even a cursory examination of climates of the countries surrounding the Mediterranean Sea would show that the Medfly is surviving and thriving in areas with climates similar to or even more extreme than that of much of California. A scientific paper published in 1931 did just such a climate comparison and concluded that the Medfly would do well in much of California.
Other "experts" tell us that the techniques we are using cannot possibly eradicate the Medfly. However, Medfly invasions into the continental United States have been eradicated a number of times, beginning with a large-scale invasion of Florida in 1929, when lead arsenate was used. The next invasion in 1956, again in Florida, was eradicated by aerial applications of food-bait sprays mixed with a small amount of malathion. In 1966 an invasion into Texas was again eliminated with aerial bait sprays. The next invasion was in the Venice area of Los Angeles in 1975 and it was eradicated with sterile Medflies, used for the first time outside an experimental situation.
Sterile flies have been components of eradication programs in 1984 and 1987 in Florida and in 1980, 1987 and 1988 in California. The most effective system is to precede the release of sterile insects with one or more aerial bait sprays to eliminate all of the mature, already fertile females and so hasten the demise of the population.
The combination technique is a proven system for eradication of isolated Medfly populations. But since there are not enough sterile flies available right now to deal with the current infestation in Los Angeles County, multiple aerial applications of malathion bait are the most effective and proven method of eradicating the pest. (We expect to have enough sterile flies to begin resuming the release program in May, thus drastically reducing aerial spraying.)
Applications of food-bait sprays using ground-based sprayers are not an effective or practical substitute for aerially applied sprays in large urban programs. It is impossible to get the necessary even coverage from ground sprayers. Such efforts, which have been made, rapidly become a logistical impossibility.
Malathion is one of the oldest and most widely used of pesticides. It is the active ingredient in numerous home and garden preparations. It has also, in certain cases, been applied to cats and dogs and used to treat humans for head lice. It is frequently used in urban areas in mosquito abatement programs. The amount of malathion that will be applied during this current eradication program will be minuscule when compared to the amount of pesticides that would be applied each year to combat the Medfly statewide if we abandon eradication efforts. We in the state food and agriculture department are working to keep pesticide usage low, but our view also encompasses the long-range effects, as opposed to the short-range (one might say short-sighted) view of these "experts."
All agencies involved in these complex programs have supported research aimed at overall pesticide usage reduction. These include improved trap systems to detect infestations, improved handling and distribution of sterile flies and improved quality-control measures to ensure sterility of the flies we release.
Other biocontrol methods have been undergoing research for decades, including the use of insect parasites against the Medfly. Early in this century, an expedition was sent to Africa to find Medfly parasites to combat a Hawaiian invasion. Over the years, many introductions have been made into Hawaii and the parasites thus established do contribute to a reduction in the Medfly population. However, the effect is nowhere near adequate, and eradication by parasites alone is not possible. Nor has research into diseases or parasite worm infections shown any effective control or eradication promise.
Thus, our options are few. To live with the Medfly would involve millions of dollars in losses and much more pesticide use in California. Do we really want that?