AirWolf  

CONTROL OF ANOPHELINE SPECIES IN THE CANAL ZONE WITH ULTRA-LOW VOLUME SPRAYS OF MALATHION AND FENTHION1

C. S- LOFGREN,2 R. M. ALTMAN 3 AND B. M. GLANCEY .2

“RESULTS. The results of the first test  (Table i) showed that applications of 0.1Ib./acre of fenthion and 0.225 Ib./acre of malathion did not give satisfactory control of anophelines in the jungle. These rates are within the range generally used for mosquito control in the United. States. When the dose of each insecticide was increased about threefold, good control was obtained (85 percent and 90-95 percent, respectively, with malathion and fenthion for as long as 25-30 hours). In the second test, fenthion was applied at the rate of 0.27 Ib./acre to three plots, but heavy rain fell on two 4-5 hours after treatment and on the third immediately after treatment. The results were as follows (the 36-hour counts are based on the  poorer control in this test can definitely he attributed to the rain on the basis of our experience with aerial sprays in Florida. Presumably this is due to "washing out" of airborne droplets or foliage residues that could kill mosquitoes that do not contact the insecticide immediately or ones that migrate into the area. All caged mosquitoes in one plot died, and 97.5 percent died in the other.”

CONCLUSIONS.

 “The results showed that control of anophelines can be obtained in moderate to dense jungles with fenthion and malathion though the necessary dose is about three times that required normally. However, this study obviously provided only a limited approach to the problem of mosquito control in jungles, and other methods besides increased doses should be investigated. A study on the relationship between droplet size and penetration through the canopy would be of particular interest.”

A PROSPECTIVE STUDY OF THE EFFECTS OF ULTRALOW

VOLUME (ULV) AERIAL APPLICATION OF MALATHION

ON EPIDEMIC PLASMODIUM FALCIPARUM MALARIA

I. STUDY DESIGN AND PERSPECTIVE*

DONALD A. ELIASON, VOLVICK R. JOSEPH, AND JALIL KARAM

Bureau of Tropical Diseases, Center for Disease Control, Public Health Service,U.S. Department of Health, Education and Welfare, Atlanta, Georgia 30333,and Service National d’Eradication de la Malaria, Port-au-Prince, Haiti

Abstract. A large-scale prospective study was designed to test the effects of aerial ultralow volume (ULV) application of malathion on epidemic Plasmodmm falciparum malaria. The study was conducted during 1972 to 1973, in the Miragoane Valley of Haiti, an area having annual anticipated outbreaks of malaria, which allowed prospective assessment. Spraying of malathion at a dosage of 4.5 fluid ounces per acre reduced populations of adult Anopheles albimanus to less than \% of prespray levels and interrupted epidemic transmission of P. faldparum malaria. No change was measured in susceptibility of the vector mosquito to malathion after six applications of spray during a period of 50 days. Ecologic study revealed no significant impact on nontarget vertebrates. Factors that contributed to the success of this method in Haiti were:

1. a susceptible population of mosquitoes

1.  suitable topography and climatic conditions for spraying; and

1.  treatment of an area sufficiently large to minimize the influence of immigration of mosquitoes from unsprayed areas.

Epidemics of mosquito-borne diseases are especially difficult to control because dispersal of infected insects may be rapid and extensive. Interruption of disease transmission through control of the vector requires a method that can be initiated on short notice and that can be used to treat large areas rapidly. Methods such as residual spraying of houses and larviciding are useful preventive measures but are of limited immediate value in control of already established epidemic transmission. Development of ultralow volume (ULV) aerial spray methodology has provided a potential tool for use in vector-borne disease epidemics. Spraying of low dosages of concentrated insecticide allows coverage of large areas with each flight of the aircraft. The efficacy of aerial ULV applications for control of vectors of human disease was clearly demonstrated in 1966 when malathion was used Accepted 13 July 1974.

*This work was supported by the United States Agency for International Development, U. S. Department of State, through PASA LA (HM 7-71).

Address reprint requests to; Center for Disease

Control, Attn; Bureau of Tropical Diseases, Atlanta,

Georgia 30333.

successfully at 3 fluid oz/acre against Aedes  aegypti (L.) in southern Florida.

1 Later in the same year, ULV malathion was used during an epidemic of St. Louis encephalitis and greatly reduced populations of the vector Culex pipiens c/uingitefasciatus Say.

2 Experience in using the ULV technique against vectors of human malaria has been limited. Efforts to control Anopheles albimanus Weidemann in El Salvador with ULV applications of malathion were not successful. Laboratory-confirmed resistance to malathion was the most reasonable explanation for the failure.

3 In the Panama Canal Zone, populations of anophelines  were reduced for a short period with ULV applications of malathion and fenthion at dosages two to three times those used in the United States.

4’5 In a later study ULV aerial applications of fenthion  were reported to be effective for several weeks when a jungle area of 20 square miles was sprayed.

6 Although effects of ULV spray on transmission of disease to man were not measured during previous studies, the clear success of this technique in controlling vector species has made it a potential tool for epidemic control.

There is seldom an opportunity to collect adequate data during mosquito-borne disease

183 184 ELIASON, JOSEPH, AND KAEAM

FIGURE 1. Ultralow volume study area, 1972-Miragoane Valley, Haiti. epidemics because of their sporadic and unpredictable occurrence. Seasonal outbreaks of malaria, however, are predictable in certain parts of the world and. therefore, allow consideration of a prospective study of the effectiveness of control methods on transmission. In 1971 a prospective study was initiated on the effects of malathion ULV aerial spray on transmission of Plasm-odium falciparum malaria during an annual outbreak in Haiti. Spraying operations took place during the latter months of 1972. The findings are summarized in four parts:

I. Study Design and Perspective;

II. Entomologic and Operational Aspects;

III. Ecologic Aspects; and

 IV. Epidemiologic Aspects.

THE STUDY AREA

An area of the southern peninsula of Haiti has  consistently experienced seasonal epidemics of malaria. The Service National d’Eradication de la Malaria (SNEM) has maintained control operations and disease surveillance in the area since 1962. The primary method has been DDT residual house spraying. Beginning in 1965, a supplemental measure of mass drug distribution was also used. During 3 years of widespread drug distribution, approximately 10% of the country’s malaria originated in this area. Following mass drug distribution, DDT spraying has remained the primary attack measure, and from 1969 up to the time of this study more than 20% of Haiti’s malaria cases have come from this area. The surveillance data from SNEM disclosed a persistent pattern of annual outbreaks  which began in October and continued through January.7 With this information it was possible to anticipate the period of epidemic transmission  and prepare for the more intensive entomologk and epidemiologic assessment required.

The study area, located between Miragoane and Petit-Goave on Haiti’s southern peninsula,  compassed three political divisions or "sections rurales"-Premiere Chalon, Premiere Plaine, and Deuxieme Plaine

(Fig. 1). The portion of the study area that was sprayed constituted approximately  20,000 acres, most of which is relatively flat agricultural land lying below 100 meters elevation. Extensive marshes surround the shallow lakes in the valley floor and these, together with numerous smaller accumulations of water, are the source of the vector Anopheles albimanus. Characteristic of many tropical regions where malaria occurs, dense sugarcane and banana groves provide natural resting places for adult mosquitoes. Mountains that rise from 300 to 600 meters above the valley floor surround the valley on all but the narrow east side, sheltering the valley from wind and providing a natural  barrier to immigration of mosquitoes from adjoining areas.

The human population of the study area was approximately 32,000, of whom 15,000 lived within the spray area. Most of the inhabitants of the area are engaged in agriculture or fishing on the fresh-water lakes, activities which do not take them far from home.

STUDY OBJECTIVES

Since the main objective of the study was to determine if ULV aerial spray could reduce established epidemic transmission of P. falciparum malaria, spray applications were scheduled to begin only after epidemic levels "were reached. Based on prior years’ data, epidemic levels were defined as 100 cases a month/10,000 population.

Epidemiologic and entomologic surveillance were intensified in the study area about 6 months before the expected peak of transmission. Surveillance methods were examined for accuracy, and steps were taken to ensure that data from the field were transmitted to SNEM headquarters  without delay.7 Entomologic surveillance was  modified to include the use of light traps as an additional sampling tool, and sites were chosen for continuous rather than periodic sampling.8 Preliminary spray tests were performed in small areas of the valley in June to assess the dosage of malathion required and to help establish the boundaries of the area to be sprayed (Fig. 1). The desired effect from the ULV spray was to reduce the potential for transmission to a very low level and maintain that level for a period of at least 6 weeks to allow epidemiologic assessment. If successful, the ULV spray was expected to cause an immediate marked reduction in the adult mosquito population of the area sprayed. Emergence of adults during the period between applications would occur, but these adults would be exposed to at least one spray application before they could become infective and transmit malaria.

During the first part of the spray period, cases of malaria would occur as a result of transmission prior to the first spray application. Continued appearance of new cases during the latter part of the spray period would be expected if the spray failed to substantially reduce mosquito populations. However, if the spray were successful, a low incidence of malaria was expected during the latter part of the spray period and for a short time after spraying was terminated.

After the last spray application, both the adult mosquito population and the incidence of malaria would return to normal seasonal levels. In designing the spray schedule, it was assumed that the extrinsic incubation period of P. falciparum was greater than 10 days; therefore, spray  applied every 10 days  would provide at least one chance to kill the adult mosquitoes before they could become infective.

Accordingly, a schedule was used that called for spraying of the area every 10 days with an extra application 5 days after the first, to achieve greater initial impact. A total of six applications were made to the area with the last being applied 45 days after the first. Mosquitoes emerging after the last application would not become infective for at least 10 days, and this would extend the period of low potential for malaria transmission to more than 7 weeks.

RESULTS AND DISCUSSION

The adult mosquito population was immediately reduced following the first spray application, the incidence of malaria subsequently declined, and finally, both the mosquito population and the incidence of malaria returned to expected  levels after spraying -was terminated.7’s These results are consistent with a conclusion that ULV aerial spray interrupted epidemic transmission of P. falciparum malaria. The dramatic reduction in the adult mosquito population was achieved without significant impact on  no target organisms.9 This is especially important because aerial ULV spraying results in complete coverage of very large areas. There was no apparent change in susceptibility to malathion even though a very large percentage of the adult mosquito population was killed on each of six applications and the larval population was also exposed to the spray. In this respect, the study represents a major departure from the traditional approach to malaria control-spraying residual insecticides (usually DDT) on interior walls of houses-which aims at a small fraction of the adult anopheline population. Because aerial ULV applications for large-area mosquito control result in exposure of most larvae and adults in the area, the chance of creating resistant strains would presumably be greater than with methods that expose only a small portion of the adult population.10 For this reason, it will be important to monitor for susceptibility to the insecticide whenever aerial ULV is used, especially in agricultural areas where prior exposure of mosquitoes to similar compounds may have increased the potential for resistance.

Economic considerations are important in any large disease control program. Mass drug distribution is presently an important measure for control of epidemic malaria, and in the area of Haiti studied here the cost of the ULV malathion application was estimated to be twice that of mass drug distribution for the same period of time. The human population density in the area was not as great as in many malarious areas, however, and this factor must also be considered.

The cost of ULV treatments per unit area is independent of the number of people living in the area. The cost of mass drug distribution per unit area is dependent on the number of people in the area and, therefore, in a very densely populated area could be more expensive than ULV spraying.

The use of ULV aerial spray is limited to areas having topographic features that will allow safe operation of the spray aircraft. Its use is also limited to time of day and season of the year when climatic factors are suitable. When air temperatures have exceeded 80 F and when wind speeds have exceeded 10 mph, ULV sprays have frequently failed to achieve satisfactory control of adult mosquito populations. In the Haiti study area, both topographic and climatic factors were optimum during the times applications were made, and uniform distribution and penetration of droplets through vegetation occurred. In areas having different topographic or climatic conditions, it may be necessary to modify dosage and/ or droplet size to achieve satisfactory results. The size of the area sprayed was an important factor in the effect of the spray on mosquito populations. Equivocal results were obtained in preliminary tests where only 5,000 acres were included, leaving unsprayed areas on three sides of the sprayed area, When the larger area of nearly 20,000 acres was sprayed, the influence of immigration was presumably reduced by the increased size and by extending the area up to natural barriers to immigration on two sides.

Important unsprayed sources of adult A. albimanv. s remained only on each end of the valley. Rapid immigration of adult culicine mosquitoes into small sprayed areas has been documented in an earlier study: Culex tarsalis populations in Hale County, Texas, were reduced by ULV malathion but were replaced in a short time by immigrating mosquitoes.11 The frequency and number of applications used in this study were probably in excess of minimum requirements- Subsequent to the first and second applications, adult mosquito populations were very small. If the remainder of the applications had been delayed, the same results might have been achieved at less expense.  This technique may be of value in the future in other areas of the world with different vectors and malaria species. When traditional methods of control have failed and where epidemic transmission is occurring by a susceptible vector, we suggest consideration of its use.

REFERENCES

1. Eliason, D. A., Kilpatrick, J. W., and Babbitt,

M. F., 1970. Evaluation of the effectiveness

of the ultra low volume aerial applications of

insecticides against Aedes aegypti (L.) in Florida.

Mosquito News, 30: 430-436.

2. Kilpatrick, J. W., and Adams, C. T., 1967.

Emergency measures employed in the control

of St. Louis encephalitis epidemics in Dallas

and Corpus Christi, Texas. Proc. 35th Annu.

Cottj. Calif. Mosquito Control Assoc., 53.

3. Brceland, S. G., Kliewcr, J. W., Austin, J. R.,

and Miller, C. W., 1970. Observations

malathion-resistant adults of Anopheles albi-

Wiedemann in coastal El Salvador.

Bull. W.H.O., 43: 627-631.

4. Lofgren, C. S., Altman, R. M., and Glancey,

B. M-, 1968. Control of anopheline species in

the Canal Zone with ultra-low volume sprays

of malathion and fenthion. Mosquito News,

28: 353-355.

5. Mount, G. A., Adams, C. T-, Pearson, W. G.,

Lofgren, C. S., and Weidhaas, D. E., 1970.

Ultralow volume aerial sprays of malathion

and fenthion for anopheline mosquito control

in the Panama Canal Zone jungle. Mosquito

News, 30: 604-610.

6. Lofgren, C. S., Dame, D. A., Johnston, L.,

Adams, C. T., Pierce, N. W., and Baldwin,

K. F., 1972. Control of anophclines in Canal

Zone jungles with ULV aerial applications of

fenthion. Mosquito News, 32: 566-573.

7. Krogstad, D. J-, Joseph, V. R., and Newton, L.

H., 1975. A prospective study of the effects

of ultralow volume (ULV) aerial application

of malathion epidemic Plasmodium falcipamalaria.

IV. Epidemiologic aspects. Am.

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Taylor, J. W., 1975. A prospective study of

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Recent developments in methods of mosquito control

Paper done by: Clifford Lofgren

“Since residual insecticide spraying in domiciles does not sufficiently control some species of anophelines to halt malaria transmission, alternate methods of control have been investigated. These include ultra-low-volume (ULV) sprays or aerosols, the release of sterile males to suppress or eradicate populations, the use of diseases or parasites to interfere with transmission or to reduce populations of mosquitos.”

“The ULV aerial sprays give practical control of Anopheles albimanus in Haiti and interrupted malaria transmission. The release of sterile males almost eliminated in isolated population of A. albimanus in a

small valley in El Salvador. Studies are in progress to evaluate the effect on populations of anophelines of a protozoan disease and to nematode parasites.”

“Another, even more successful, demonstration of the practical application of the ULV technique was made in Haiti by the Center for Disease Control, US Public Health Services (10-12). The test area of about 8100 ha was located on the southern peninsula of Haiti in an isolated valley surrounded on three sides by mountains. Falciparum malaria was highly endemic in the area: less than 1% of the total population of Haiti lived in the valley, but this proportion accounted for over 20% of the malaria in Haiti between 1969 and 1971.The main objective was to determine whether sufficient control of A.albimanus could be obtained with ULV malathion to affect the transmission of malaria. In all, 6 aerial applications were made from 27 October to 16 November with a twin engine aircraft fitted with flat fan spray nozzles, at a rate of 439ml of malathion per ha for the first applications were made in the morning when meteorological conditions were favorable (wind velocity ‹4.8 km/h and air temperature ‹27⁰ C); 4-5 days were required to complete each treatment. “