W. L. Brown, Jr.
Mass Insect Control Programs: Four Case Histories.
Psyche 68:75-111, 1961.

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MASS INSECT CONTROL PROGRAMS:
FOUR CASE HISTORIES*
BY WILLIAM L. BROWN, JR.
Department of Entomology, Cornell University PREFACE
Insect control is a vast subject. It encompasses many methods of approach meant to protect a wide diversity of human resources, in- cluding the lives and health of humans themselves. Upon the success or failure of insect control programs have rested the fate of armies, of great canals and populous lands. Yet, though man has registered many practical successes against particular insect menaces, we do not yet understand fully the underlying dynamics of insect populations or for that matter, of other animals, including man himself), and until we do, perfect control will probably continue to elude us in many cases.
However, there exist practical measures that have been used suc- cessfully to control or eradicate many kinds of insects, even though Figure 1. Insecticide sales by U. S. producers in recent years, projected through to the end of 1961. Domestic consumption of insecticides actually declined slightly during 1960 in the U. S., but exports more than made up this dip. From Chemical Week, July 22, 1961, by permission. *This study and the report were sponsored and supported by the Conserva- tion Foundation. New York.




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76 Psyche [June-September
we may not understand exactly how a particular measure takes its effect. In recent years, developments in practical insect control have come thick and fast, particularly in the field of pesticides. The de- velopment since World War I1 of chlorinated hydrocarbons, carba- mate and organic phosphate insecticides, distributed by mass aerial spray techniques, has revolutionized control work and has raised insec- ticide production and aerial application to the status of big businesses. But, pr~m~ising as it seemed in the immediate postwar years, simple mass aerial broadcasting of toxic materials has not always led to : fficient control of the target pest. Furthermore, the extensive application of this relatively unselective technique inevitably caused damage to in- cidental targets - plants and animals or property valued by humans - and there even arose a threat to human health *O As such damage and threat of damage became more obvious, protest against mass air-spraying increased in volume, and naturally the demand grew for research into alternative means of control. It is my intention now to attempt to illuminate the current status and outlook of insect control methods in the United States by out- lining four case histories of large-scale insect control programs. It is difficult to say how representative these case histories may be, considering the very diverse nature of insects and the damage each kind does. All four of the programs are large and expensive ones as such operations go, all have been considered to be eradication programs at one time or another, and all have been guided or conducted by agencies of the United States Department of Agriculture (hereinafter referred to as USDA).
Since these great programs affect or involve many people and many diverse vested interests, they are all to some extent controversial. Because controversy about them involves many contradictory findings and interpretations, it is often difficult to gain a true and unbiased conception of what is going on in a given instance. For this reason, I have tried to draw my information from as large and varied a group of sources as I could find (see Acknowledgements and References Cited). Let us now see if a resume of four programs - Gypsy Moth, Fire Ant, Mediterranean Fruit Fly and Screwworm - will help us to appreciate the problems of mass insect control. THE GYPSY MOTH
Introduction
The Gypsy Moth, Porthetria disw (formerly Lynzantria dispar), is a variable insect, a native of Eurasia, where it ranges from Portugal and North Africa to Japan. The insect was imported to the Boston



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area from France in 1869 by a misguided naturalist who believed that he could cross it with silk~orm~s. Moths escaped from his breed- ing colony, but it was not until 1889 that the first severe outbreak defoliated fruit and shade trees in many towns of eastern Massachu- setts. Control work was started by the state and apparently was successful, for populations were so low by 1899 that control operations were ended. The moth soon again built up extensive populations, and control work was resumed in 1905, but it had spread by this time to western Massachusetts and parts of Maine, New Hampshire and Rhode Island. In 1906, Congress voted aid to the infested states to help pi-event the spread of the moth, but despite all efforts it con- tinued to expand its range.
Biology and Nature of the Damage
The gypsy moth has a single generation per year. The winter is passed in the egg stage, and in New England the larvae hatch in mid- spring and feed through May and June, entering the quiescent pupal stage in early July. The larvae feed on a wide variety of broad-leaved trees and shrubs, especially oak, willow, poplar, birch, fruit trees and, in heavy infestations, even hemlock and pine. Dense populations may completely defoliate large areas of forest, weakening many trees and killing others outright.
The heavy-bodied female does not fly, but puts out a powerful scent to which the strong-flying male responds, even to extremely minute amounts carried on the air great distances, by flying upwind until contacting the source individuals and copulating with them.^ The female deposits her eggs on tree trunks, fences, rocks and other solid objects. The young larvae spin silken threads on which they are easily spread by the wind before they start to feed. According to Campbell4 the strong fluctuations in abundance of the moth are density-reactive, a most critical factor in this reactivity being the larval behavior. At low densities, the caterpillars tend to descend to the leaf litter to rest during the daytime, and feed mainly at night out on the foliage. When density is intermediate, the larvae rest during the day under loose bark on the tree trunks, a habit that has been used to advantage in control work (bands of burlap placed around trunks of infested trees are removed daily and the caterpillars found beneath them are destroyed). At high densities, the larvae remain on the foliage day and night, and are subject to heavy losses due to disease, desiccation and attack by ichneumon-wasp parasites. Population "crashes" are correlated with previous high densities of larvae.




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Control Problems
Early control efforts by the State of Massachusetts and the Federal Government included laborious and expensive methods such as hand- creosoting of egg masses, shelter-band and tanglefoot trapping on tree trunks, and various kinds of spray operations from the ground. For many years, control and quarantine programs appear to have confined the infestation to the area east of the "barrier" at the Berkshires and Gren Mountains. Occasional extralimital infestations appearing in New Jersey, Ohio, Pennsylvania and Canada, particularly after egg masses were spread widely by the hurricane of 1938, apparently were eradicated before getting out of hand.
Extensive introductions of
predatory and parasitic insects from Europe and Japan were made beginning in 1905, and about ten such insects have taken hold in North America.
Much of the subsequent history of the infestation was summarized in the report of the Gypsy Moth Eradication Meeting" held in Ithaca, New York. in September, 1957: "Following World War II, DDT was found to be a specific insecticide for the gypsy moth. At about the same time applica- tion of insecticide by plane became a practical undertaking. It was a new day for gypsy moth control. Heavy infestations within the area of general spread were suppressed or brought under control, and new infestations beyond the barrier were detected and held in check. Pennsylvania eradicated with reason- able effort and expenditure the gypsy moth on an area of 300,000 acres. Unfortunately more than 20 million acres were infested in this country before a practical control was discovered. For some unexplained reason, the gypsy moth infestations seemed to explode* in 1950 and there was rapid spread beyond the bar- rier zone. Following the outbreaks in 1953 and 1954, surveys revealed the new areas of infestation west of the barrier zone in New York, New Jersey and Pennsylvania, aggregating nearly 9 million acres. An isolated infestation found in the vicinity of Lansing, Michigan, was immediately scheduled for eradication. The occurrence of these infestations west and south of the barrier posed a serious threat of spread to the hardwood forests through- out the eastern and southern United States. The control and
quarantine programs that had successfully held the moth in check for so long were no longer adequate. . . . " *The explosion might better be said to have fairly begun in 1951 or 1952 ; see Figure 2.
its inception so soon after mass air spraying of DDT began on an operational basis is a phenomenon which, curiously enough, seems to have attracted little attention. It was first pointed out to me by Prof. F. M, Carpenter of Harvard University. - W L, B,



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2 mlll!on
ACRES
SPRAYED
BY AIR
YEAR
4 -
2 -
I m~ll~on -
DEFOLIATED
YEAR
Figure 2. Graphs to' show the ups and downs of the struggle against the gypsy moth in the U. S. Acreage showing substantial defoliation by gypsy moth larvae each year (below) is compared with acreage sprayed from the air
(above) mostly with DDT at 1 Ib per acre. Some suppression treatments used only 1/2 or 3/4 Ib of DDT per acre, and sevin has partly replaced DDT in recent years. For details, see summaries by USDA in Appendix A, upon which these graphs are based.




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In spite of the difficulties involved, Federal and some state authori- ties were still speaking in terms of "eradication" of the gypsy moth in 1956 and 1957, while other state and local people were by this time hesitant about backing an all-out eradication effort. In 1957, after about three and one-half million acres had been sprayed (two and one-half millions of them in New York State), DDT residues were found on forage crops and in the milk of cows that had grazed on treated areas in New York State, as well as in eggs from poultry farms that had received spi-ay.16 DDT tolerances for milk are set at zero by the Federal Food and Drug Administration and by health authorities in New York among other states. When the DDT residues were found persisting on forage crops and in the raw milk for periods up to a year, New York suspended eradication efforts ". . . so that," as the USDA's Cooperative Plant Pest Control Programs for 1958 put it, "the 1957 work could be fully evaluated and any required 'mopping up' could be done; how- ever, during the eradication season tests were made of several alternate insecticides more suitable than DDT for use on pasture and forage crops.''
Since 1958, New York has been doing a greatly reduced amount of spraying by air, using in part the new insecticide sevin, a carbamate having very low toxicity to mamm.als and birds, and one leaving no residue in the milk. Unfortunately, sevin is not as good against the gypsy moth as is DDT, it is highly toxic to honeybees, and it injures plants to some extent.
Aside from the dairy-linked residue problem, DDT has received rather good marks from most biologists checking the general ecological effects of mass spray at one pound to the acre. A few fish are some- times killed, birds that catch insects on the wing depart, and certain aquatic insects suffer, but the known damage does seem tolerable. Long-term residual effects on soil organisms are, however, not well known.
The chief short-range danger of mass aerial DDT campaigns lies with the loose spray practices or accidents that result in duplication (or worse) of spray strips in a given area. Field insect control men often complain about the quality of pilots available for some spray programs, and numerous incidents have occurred to illustrate the point that some of the pilots are irresponsible or incompetent, or that they are poorly directed. For this and other reasons, it seems certain that operational mass spraying does not always give the same safe results as are found for the neatly-sprayed test strips of some of the studies, and landowners are often justified in complaining of double or triple



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doses of spray on their land. In view of these difficulties, DDT must be considered as only a marginally safe compound even at the I lb per acre dosage.
The issue of mass spraying has come to one court battle that at- tracted considerable attention. A group of plaintiffs led by Dr. Robert Cushman Murphy, the well-known ornithologist, sought injunctions against mass spraying of DDT for gypsy moth on or near their land, which was situated near New York City and mostly on Long Island. Most of the plaintiffs were organic gardeners and nature-lovers, and much of their testimony tended to be emotional in tone but rather insubstantial as to verifiable facts. The government defended itself with toxicologists and entomologists who presented a generally factual picture, and the case was decided against the plaintiffs by the Federal judge, although he warned the government to use more care in spray operations. The main effect of the case appears to have been to make the spray agencies hesitant about treating Long Island and many other farm areas. Also, by agreement with New York health authorities, a wide belt is left unsprayed around the large reservoirs of the metro- politan water supply. Such areas can of course provide refuges for the moth from which it is potentially able to recolonize adjacent treated areas.
Thus, for various reasons, the large key "border state" of New York has in fact been forced to abandon the "eradication" campaign, and the Plant Pest Control Division of the USDA now speaks instead of a "containment program" which would include chemical treatments within the infested area and along its periphery to back up the con- tinued quarantines.
Infestations in Pennsylvania and Michigan, thought on several past occasions to have been eradicated or nearly so by DDT spray, still survive. Directly menaced are the hardwood forests of the Atlantic Slope, the Appalachians and the Mississippi Valley. What Can Be Done About the Gypsy Moth?
I gather from conversations and correspondence with entomologists and foresters responsible for gypsy moth control at the state and local level that they generally share an uneasiness about the use of air- sprayed non-specific poisons such as DDT and sevin on forest and watershed areas. Most of them expressed the hope that some substitute control method eventually would be found. So far as we can see now, potential substitute methods lie in four different areas: predator- parasite manipulation, propagation of bacterial or viral diseases,



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baiting with attractants, and genetic disruption. In briefly discussing these topics, we should not overlook the ~ossibility that there may exist entirely different modes of attacking the ~roblem that have not yet occurred to anyone.
Predators and parasites. As already mentioned, a number of predaceous, parasitic and parasitoid insects, mainly beetles, flies and wasplike types, have been successfully colonized in the United States after being brought from Europe and Asia. Different ones attack every stage of the moth, from egg through adult, but few of them are strictly specific to the gypsy moth. The efficacy of the parasites is now open to question, since they have obviously not prevented serious outbreaks in areas where they are known to be established. Never- theless, some natural enemies are known to be very effective at high densities of the host, and their value in the absence of possibly disturb- ing chemical control has not been thoroughly checked in recent years. Furthermore, it is likely that the established introductions represent only a fraction of the potentially useful arthropod enemies of the moth existing in Eurasia or elsewhere. In theory at least, there remains the possibility of keeping the moth at a tolerable population level by means of natural enemies, especially if used in conjunction with other biological control methods. Further research on natural enemies of the moth would certainly be desirable.
Disease propagation. The gypsy moth larva is susceptible to certain bacterial and viral diseases, among which Bacillus thuringiensis shows enough promise to have stimulated large-scale tests by Federal and state agencies. These tests, only partly completed, employ a "sticker" of tung oil or one of the improved English Lovol products to fasten the bacterial spores to the foliage. The suspension of spores in sticker can be sprayed from the air, and presumably is not harmful to plants or wildlife. So far, results have not been encouraging. Attractants. The female gypsy moth, as already stated, can flutter along the ground or over low plants, but she cannot truly fly for any distance. The strong-flying males, like those of many moths, are strongly activated, even over long distances, by scent released by the female from the terminal segments 01- "tip" of her abdomen. Upon sensing even minute amounts of this scent, the male responds by flying upwind, in this way automaticallv approaching the scent-producing female, and ultimately coming near enough to mate with her. The scent obtained by extracting the female tips in benzol has been used for years as a lure in metal or paper traps to survey suspected areas in order to determine whether males, and therefore a likely infestation, are present. The female tips are obtained by the laborious and extremely expensive rearing of thousands of hand-collected female



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pupae, many of them imported from Europe and North Africa. Costs have ranged up to a half dollar per tip in poor collecting years. In 1960, after producing several moderately effective synthetic lures, M. Jacobson and his co-workers of the Entomology Research Division, Agricultural Research Service, USDA, succeeded in isolating the principal sex attractant from. some half a million female gypsy moth tips collected in Connecticut and Spain. The substance was prepared synthetically and found to be an ester alcohol with 16 carbon atoms in its main chain. In the course of preparing the natural lure, a closely related substance (with 18 carbon atoms in its main chain) was also found to act as a strong gypsy moth lure.17 This preparation, named gyplure, has the advantage that it can be synthesized cheaply and in quantity from ricinoleic acid, a common component of castor oil. Tested in field traps, quantities of this substance as small as one microgram proved equal in luring power to traps baited with the natural lure. In 1961, as this is written, field trials are being carried out to test the efficacy of gyplure-toxicant combination baits in re- ducing moth populations.
Included in this program are "confusion" tests with saturated levels of gyplure in granular and spray formula- tions, Initial technical difficulties have been met, but it is hoped that these can be cleared up during the 1962 season. It will be appreciated that many hopes ride on these crucial trials. Genetic methods. The success of the screwworm eradication pro- gram (see below) has raised the possibility that the release of sterilized males might be used to control or eradicate gypsy moth populations. This possibility remains to be explored by further studies of the moths' mating behavior and physiology and the practicability of rearing, sterilization and release procedures. Sterile male release might be made much more effective after reduction of the population by bait attractants or other means.
Other theoretical possibilities for control rest in the fact, discovered years ago by R. B. Goldschmidt, that certain different native Old World populations of P. dispar differ in their sex-determining mech- anisms in such a way that crosses made between them produce inter- sexes. It can be argued that the overall fitness of a population might be cut by introducing north Japanese strains into the American populations, which originated in France. The possibility is worth investigation despite some theoretical difficulties. THE IMPORTED FIRE ANT
Introduction
The fire ants belong to seven or eight New World species in the qeminata group of genus Solenosis. The group as a whole has a



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tropical warm temperate distribution throughout the Americas, from southeastern and southwestern U. S. to central Argentina and Chile. The species are quite closely related and are similar in their habits. All form populous nests, at maturity containing 25,000 to more than 200,000 active and aggressive adult workers. The workers in a mature nest vary considerably in size from large soldiers down to much more numerous minor workers only 2-3 mm, long, and usually only a single functional queen is present. Nest foundation follows the pattern typical for ants, in which virgin winged females mate with males during a nuptial flight, then quickly shed their wings and, as young queens, burrow into the soil and begin the rearing of the first brood in a small chamber. Later, as the nest grows, it usually comes to be capped by an earthen mound sometimes two feet or more high and often two or three feet in diameter. Up to the First World War, only three of the fire ant species were known to occur in the U. S., of which two, Solenopsis xyloni and S. geminata (native fire ant) were found in the southeastern states. It seems possible that the "native" fire ant is itself a post-Columbian introduction, and it has been spread widely over the tropics of both hemispheres by human commerce. In past years, S. geminata had gathered to itself much the same reputation as a nuisance now gen- erally assigned to the late-coming imported fire ant (8. saevissima) that is the subject of this discussion. The imported fire ant arrived at Mobile, Alabama in produce or ballast at or a few years after the end of the First World War.
At first the ant (then represented
solely, so it seems, by a blackish phase with a dull orange band at the base of its gaster - the so-called "variety richteri," common in Argentina and Uruguay) spread only very slowly in Mobile and its environs. At some time around the beginning of the I~~o's, a smaller, light reddish form of saevissima appeared in the Mobile area. This phase corresponds to populations of the species common in southern Brazil and Paraguay, and it seems most likely that its appearance marks a second introduction of saevissinza into the Mobile Bay port area.
Coincident with the advent of the red phase, the entire saevissiwa salient in southern Alabama entered upon a period of rapid expansion that carried the main infestation across state lines by 1940. The expansion apparently has not yet reached its full extent, although infestations are or have been known to occur in ten states ranging from Texas and Arkansas to North Carolina and Florida. Expansion occurs in two main ways -by steady widening of the main infested areas due to short-range aerial spread of winged females, and through



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colonization ahead of the main infested area by queens and colony fragments transported by vehicular traffic. Nursery stock used to be a prime source of new infestations, but since nursery treatments and quarantine regulations have come into effect, fertilized females acci- dently carried in automobiles are probably responsible for most colonization.
Wherever the red phase has expanded to overcome the dark phase. the two extreme forms have interbred to produce a series of inter- mediates, and in most cases the red form soon comes to. predominate by a process of genetic swamping coupled with its greater success in warfare between nests. In fact, it may not be too extravagant a speculation to conclude that it was the injection of the red-form genes into the existing dark population that sparked the spectacular spread of the species in the last three decades. At present, the North Ameri- can population consists miainly of light reddish ants, the dark phase surviving mainly in peripheral situations and cool swamplands. Wherever it spreads, S. saevissinza tends to replace the populations of S. xyloni and S. qeminata in its path, though this is less true of the dark-colored geminata occupying woodlands in Florida and per- haps elsewhei-eZG ; saevissima in the U.S. generally avoids shaded situa- tions. The imported fire ant is able to build up remarkably dense populations. I have seen pastures in eastern Mississippi in which it was literally possible to walk for a considerable distance by stepping from mound to mound without touching a foot to the ground between. Such situations are exceptional, and usually mark the entry of the species into a new area, or else follow control measures that have knocked out a stable population of old, large nests. When the old nests are eliminated, large numbers (up to 185 per acre) of smaller new ones take their places, but as they grow, nests are gradually eliminated until the density is again relatively low (10-50 nests per acre usually).
Studies made to date have not been critical enough to detect possible widespread population fluctuations in untreated areas, but about a century ago, Bates noted a radical change in a native population of S. saevissima in the Amazon Basin.
A small number of parasites of this ant are known in its native habitat, including several known or suspected inquilinous species of ants and a phorid fly, but no real study has ever been made of this phase of the ant's biology. These parasites have been lightly dismissed as a control possibility by previous writers, but it seems to me that the