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Memórias do Instituto Oswaldo Cruz
Fundação Oswaldo Cruz, Fiocruz
ISSN: 1678-8060 EISSN: 1678-8060
Vol. 90, Num. 3, 1995, pp. 421-424
Mem Inst Oswaldo Cruz, Rio de laneiro, Vol. 90(3): 421-424, may/jun. 1995

An Attempt to Control Phlebotomine Sand Flies (Diptera: Psychodidae) by Residual Spraying with Deltamethrin in a Colombian Village

B Alexander, C Jaramillo, MC Usma, BL Quesada, H Cadena, W Roa, BL Travi

Centro Intemacional de Entrenanuento e Investigaciones M6dicas (CIDElM), A.A. 5390, Cali, Colombia


Code Number: OC95082
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An attempt was ngule to control phlebotomine sand flies biting indoors in a rural community near Cali, Colombia, using the residual insecticide K-Othrine' (deltamethrin) sprayed on the inside wails of houses. Twelve houses were divided into matched pairs based on physical characteristics, one house in each pair being left untreated while the inside walls of the other were sprayed with 1% deltamethrin at a concentration of 500 mg a.i/m. Sand flies were sampled each week using protected human bait and sticky trap collections for four months after spraying. The number of sand flies (Lutzomyia youngi) collected on sticky traps was significantly lower (P= 0.004) in the untreated houses than in the treated ones with which they were matched This difference was not significant for L. columbiana; the other anthropophilic species were not present in large numbers. The numbers collected on human bait in treated and untreated houses were not significantly different for either species. Activity of the insecticide as determined by contact bioassays remained high throughout the study and failure to control the insects was attributed to two factors: the tendency of sandflies to bite before making contact with the insecticide and the fact that the number of sand flies that entered houses represented a relatively small proportion of the population in the wooded areas surrounding the settlement in the study.

Key words: Lutzomyia youngi - Lutzomyia columbiana - deltamethfin - sand fly control - Colombia

Phlebotomine sand flies (Diptera: Psychodidae) are highly susceptible to insecticides and in certain areas effective control of these insects has been achieved as a side-effect of malaria eradication programmes, in which the walls of houses are sprayed to kill resting Anopheles mosquitoes (Vioukov 1987). Residual formulations of di- chloro-diphenyltrichloroethane (DDT) have also been used in many areas to specifically control sand flies, particularly in the Old World (Jacusiel 1947, Hertig 1949, Pandya 1983), but also in Peru (Hertig & Fairchild 1948). The synthetic py- rethroid deltamethfin has also been used against sand flies in Bolivia (Le Pont et al. 1989) and Brazil (Falcao et al. 1991, Marcondes & Nascimento 1993). Nevertheless, rather less information is available on the control of New World sand flies, which tend to live in ecologically more complex habitats than their Old World relatives of the genus Phlebotomus and have less predisposition to enter houses and bite. As such American cutaneous leishmaniasis is often considered to be acquired principally in extradomiciliary and occupational situations (Lainson 1983), where vector control by conventional methods would be difficult or impossible.

Although the above is true for many situatious, in others there is evidence of intradomiciliary transmission of Leishmania (Escobar et al. 1992), generally based on the presence of cutaneous leishmaniasis cases among babies or infants who would not normally be outdoors when sand flies are active. Another factor that should however be taken into account is the ambient temperature after dark. In mountainous areas of the Neotropics such as the Andes of Colombia this may fail considerably, forcing local inhabitants to wear heavy clothing or remain indoors, both of which reduce their exposure to the bites of sand flies. Indoor biting in such situations therefore assumes great imporlance and sand fly control by conventional means becomes more feasible. These control measures include the use of impregnated bednets and curtains to cover doors and windows as well as the application of residual insecticides to walls.

This article reports the results of a four-month pilot study on the efficacy of "K-Othrine" (deltamethrin applied as a residual spray to the walls of houses to reduce the biting nuisance caused by sand flies in a settlement near Cali, Colombia.

MATERIALS AND METHODS

Preliminary observations - The study was conducted at Alto Aguacatal, a small settlement within the city limits of Cali, Colombia, between November 1992 and March 1993. The village lies at an altitude of approximately 1770 m above sea level and consists of 13 houses, the majority constructed of adobe. The inhabitants of Alto Aguacata/are agricultural workers, coffee being the main crop. Mean annual temperature of the village is 20 C.

Although no cases of cutaneous leishmaniasis have been reported from Alto Aguacatal, the inhabitants complain of the nuisance caused by "palomillas" (phlebotomine sand flies) which enter houses after dark and bite throughout the night, particularly at certain periods of the year. Most people remain indoors after dark since temperatures drop sharply in Alto Aguacatal after sunset, this fall often exacerbated by cloud descending from the surrounding mountains.

Two sampling methods were employed to determine which species of sand flies bit indoors and estimate the biting rate. The first consisted of human bait collections in which volunteers collected sand flies that landed on them during the two hours of peak sand fly activity (19:30-21:30, or the first 2 hr after sunset) using a mouth aspirator. These insects were killed and immersed in a 5% detergent solution for 48 hr to clear tnem sufficiently for taxonomic characters (female spermathecae and extemal genitalia of males) to be distinguished. Although this method is slower and less effective than using agents such as lactophenol, it was found to be adequate for the relatively small numbers of insects collected during the study.

The second sampling method involved hanging six sticky traps (sheets of unwaxed paper coated in castor oil) on each of two lines hung parallel to one of the walls at 2 m and 30 cm above the floor of each dwelling. Sticky trap collections were made in six of the houses for seven weeks prior to the study. These traps were inspected each week, when sand flies were carefully removed by mounted needle, stored in 5% detergent solution for 48 hr to remove the oil and then identified to species.

Extradomiciliary sand fly activity was determined by making Shannon trap collections in wooded areas surrounding the houses, again between 19:30-21:30 hr.

Insecticide trial - The twelve houses used in the control study were divided into six matched pairs, based on features that might affect absorption of insecticide (wall area, construction material), sand fly density (proximity of wooded areas (number of doors and windows, number of in- habitants, presence of domestic animals). One house in each pair had its walls treated with a 1% wettable powder formulation of "K-Othrine" (deltamethrin) at a concentration of 500 mg ai/m^2 using a knapsack sprayer fitted with a fan nozzle.

The other house in each pair was left untreated. This insecticide was selected because of its high safety coefficient (the acute oral LD50 of K-Othrine for rats is 5560 times that for house flies, whereas comparative values for DDT and malathion are 11.3 and 50 respectively) and low vapour pressure (2 x 10 mbar at 25 C).

Numbers of sand flies in treated and untreated houses were determined as before. Since it was not possible to make human bait collections in all of the houses every week, biting catches were restricted to three dwellings of each category selected at random each week.

RESULTS

Preliminary observations - The sand fly fauna of Alto Aguacatal was found to consist of three anthropophilic species, of which Lutzomyia youngi Feliciangeli & Murillo was the most numerous, comprising 56.5% of sticky trap collections and 67.6% of sand flies collected in the Shannon trap. Next in importance was L columbiana (Ristorcelli & Van Ty), which constituted 46.6% of sticky trap and 27.3% of Shannon trap collections. The third species, L lichyi (Floch & Abonnenc) made up only 1.8% of sticky trap col- lections and 4.9% of those made by Shannon trap. Although all three species have been infected with Le. brazilienis in the laboratory (Warburg et al. 1991) and may be involved in the transmission of this or other Leishmania species; in southwestern Colombia, to date there have been no reports of cutaneous leishmaniasis from Alto Aguacatal. Note that Warburg et al. (1991) misidentified L youngi as the closely related. Townsendi (Orfiz), females of the two species being morphologically identical. The possible role of L youngi in Leishmania transmission in Vene- zuela is discussed in Feliciangeli et al. (1992).

Mean number of sand flies/house/week collected on sticky traps prior to the intervention varied between 0.3-5.0 for L youngi and 0.2-7.5 for L columbiana. Extradomiciliary activity of these species as determined by Shannon trap varied between 4.5-36.5/man-hr for L youngi and 5.0-11.5/man-hr for L columbiana.

The number of sand flies of both species collected on sticky traps during the four months after spraying is shown in Table I. Analysis by Wilcoxon 2-sample test revealed that the number of L youngi collected in treated houses was sig- nificantly larger than that in untreated houses. A significant difference was not seen in L columbi-caught by sticky trap in treated houses was higher than that in untreated houses. The difference between the numbers collected in treated and control houses was most marked in pair 1, in which sticky traps in the treated house collected 67.8% of all L youngi and 62.8% of all L columbiana taken during the study.

TABLE 1

Number of sand flies collected by sticky traps in houses treated with 1% deltametluin or left untreated, Alto Aguacatal, Colombia

-----------------------------------------------------------
                        Total No. 
-----------------------------------------------------------
Species                Treated Control    T/C      P
                                          ratio 
-----------------------------------------------------------
Lutzomyia youngi        546      63       8.7:1   
0.004 
Lutzomyia 
columbiana              436      80       5.4:1    ns
-----------------------------------------------------------

The results of human bait collections are shown in Table II and suggest the opposite of the relationship seen based on sticky trap collections for treated and untreated houses. Overall numbers of sand flies of both species caught on human bait was higher in untreated than treated houses although these differences were not found to be significant when analyzed by Wileoxon sample test.

Insects from a laboratory colony (FI) of L youngi were used in contact bioassays 76 and 109 days after application of the insecticide, in which 10 sand flies were introduced into each of three plastic cones of base diameter 10 cm fixed to the wails of treated and control houses. Mortality of sand flies in the treated group after 30 mill was 100% in both trials, while control mortality was less than 10%.

DISCUSSION

The length of the study (131 days) was well within the period in which the insecticidal efficacy of K-Othrine sprayed on adobe walls is thought to remain undiminished, the manufacturers recommending repeat applications at sixmonth intervals (P Walker, Roussel-Uclafl SOVA, pers. comm.). Quesada (1993) found that the mortality of L youngi exposed for 30 min to adobe treated witit deltamethrin at a concentration of 25 mgJm remained at 100% up to 90 days after application, falling to 86.7% after 120 days.

The number of houses treated during the present study was probably too low to affect population levels of sand flies to a marked extent in Alto Aguacatal, since the insects entering the six treated houses to bite probably represented a small fraction of the total sand fly population of the village. The highest recorded biting rate for any of the intradomiciliary human bait collections was 28 per man-hr, although most samples were much smaller. Nevertheless based on the results shown in Table II it does appear that residual spraying of walls with deltamethrin may. have reduced biting by sand flies, although not the amount of sand flies that entered houses. The sand flies that were collected off human bait in treated houses may have been those that alit on the volunteers without touching the insecticide beforehand, since contact with deltamethrin is known to have a repellent/excitatory effect that would reduce the predisposition of these insects to feed. Herrer (1956) noted that L verrucarum (Townsend) in Peru often entered houses without touching walls, took a blood meal, then flew outside again without ever making contact with walls treated with DDT.

The high number of sand flies caught on sticky traps in treated houses may he explained by reduced mobility of the insects after touching the walls. While sand flies that took a blood meal in untreated houses could fly outside immediately afterwards or after resting briefly on the walls, those alighting on the walls of treated houses after feeding would make contact with deltamethfin, resulting in intoxication and reduced flying capability. These insects would therefore spend more time inside the houses and have a greater possibility of coming into contact with the sticky traps. Sand flies with fresh blood meals (not from the volunteers) were seen resting on the walls of untreated houses on several occasions.

TABLE II

Number of sand flies collected/man-hr on human bait on in houses treated with 1% deltamethrin or left untreated, Alto Aguacatal, Colombia

------------------------------------------------------------
              Mean No./man-hr+/- 1 SD
------------------------------------------------------------
Species                 Treated    Control    T/C ratio    P 
------------------------------------------------------------
Lutzornyia youngi       0.70+/-0.74  2.95+/-3.50 
0.24:1 ns
Lutzomyia calumbiana    0.45+/-0.73  0.83+/-0.42 
0.54:1 ns
------------------------------------------------------------

Le Pont et al. (1989) found that treatment of interior and exterior walls of houses and animal shelters in Yungas, Bolivia was very effective against

wall longipalpis (Lutz & Neiva), which disappeared for up to ten months after spraying. The effect on L nuneztovari anglesi Le Pont & Desjeux was less marked, probably due to the more exophilic behaviour of this species. Falcao et al. (1991) found that indoor spraying was effective in reducing the numbers of sand flies [principally L intermedia (Lutz & Neiva) and L migonei (Francs)] biting inside houses in Viana, Brazil. In another Brazilian study, Marcondes & Nascimento (1993) found L longipalpis on some walls treated with deltamethrin only 14 days after spraying. While our results suggest that residual spraying of walls is an effective method of reducing sand fly biting, it should be noted that none of the families participating in the study perceived a significant difference after treatment. This was particularly true in the house where activity of the insects was greater, and biting was recorded by the inhabitants within 48 hr of treatment of the walls of their house. This may have been the resuit of sand flies entering and biting before making contact with the treated surface.

If sand fly populations in wooded areas surrounding the dwellings were sufficiently large to offset losses then the beneficial effects of insecticidal treatment would not be discerned by the occupants of treated houses. It is possible that prolonged use of residual insecticides might be effective in reducing population levels to suca an extent that the numbers of sand flies entering houses is significantly diminished. However the unwillingness of several of the families in Alto Aguacatal to continue participation in the study after four months meant that this could not be measured.

Apart from the fact that sand flies may bite before contacting treated surfaces, use of residual insecticides sprayed on walls to Control sand flies has the disadvantages of requiring trained personnel and special equipment. In communities as small as Alto Aguacatal these measures may not have a significant effect on the sand fly populations, especially if not applied by most or all households in the community. An alternative strategy would be the use of impregnated mosquito nets that can be treated with insecticide regularly by the members of rural communities themselves and offer more complete protection, at least after the users have retired for the night. Impregnated ctulains hung across doors and windows would offer some protection before the occupants of a house have gone to bed. In some situations, however, residual insecticides sprayed on the walls of houses may offer a viable strategy for control of sand flies and leishmaniasis if local governmental or community organizations provide infrastructure to sustain such a programme.

ACKNOWLEDGEMENTS

To Javier Palta, James Montoya, Sandra Escobar, Carolina Chamorro and Melba Hoyos for assistance with field sampling. To SOVA de Colombia S.A. for supplying the K-Othfine, Mr Antimo Sotelo of the Malaria Eradication Service for insecticide application and Miss Dufay Lorena Villalbs for assistance with preparation of the manuscript.

REFERENCES

Escobar MA, Martinez F, Smith FS, Palms GI 1992. American cutaneous and mucocutaneous leishmaniasis (tegumentary) a diagnostic challenge. Trop Doc (Suppl) 1: 69-78.

Falcao AL, Roeha Falcao A, Texeira Pinto C, Ferreira Gontijo CM, FaIqueto A 1991. Effect of deltamethin spraying on the sandfly populations in a focus of American cutaneous leishinaniasis. Mem Inst Oswaldo Cruz 86: 399-404.

Feliciangeli MD, Arredondo C, Ward R 1992. Phlebotornine sand flies in Venezuela: Review of the verrucarum species group (in part) of Lutzomyia (Diptera: Psychodidae) with description of a new species from Lara. J Med Entomo 129: 730-744.

Herrera 1956. Phlebotomns y DDT en el Peru. Experimentos sobre control de la Vermga y la Uta. Rev Med Exp (Lima) 10: 99-137.

Herlig M 1949. Phlebotomus and residual DDT in Greece and Italy. Am J Trop Med Hyg 29: 773-809.

Herlig M, Fairchild GB 1948. The control of Phlebotomus in Peru with DDT. Am J Trop Med Hyg 28: 207-230.

Jacusiel F 1947. Sandfly control with DDT residual spray. Field experiments in Palestine. Bull Entomol Res 38: 479-488.

Lainson R 1983. The American leishmaniases: some observations on their ecology and epidemiology. Trans R Soc Trop Med Hyg 77: 569-596.

Le Pont F, Manseal Padilia J, Desjeux P, Richard A, Mouchet J 1989. Impact de pulverisations de deltamefluine dans un foyer de leishnumiose de Bolivie. Ann Soc Belg Med Trop 68: 223-232.

Marcondes CB, Nascimento JA 1993. Avaliaqao da eficiencia de deltametrina (K-Othrine CE) no controle de Lutzomyia longipalpis (Diptera: Psychodidae), no municipio de Santa Rita, Paraiba, Brasil. Rev Soc Bras Med Trop 26: 15-18.

Pandya AP 1983. Impact of antimalaria house spraying on phlebotomid population in Surat district, Gujarat. Ind J Med Res 78: 354-360.

Quesada BL 1993. Evaluacion de la susceptibilidad en condiciones de Laboratorio de Lutzomyia spp. (Diptera: Psychodidae) a varios insecticidas, Undergraduate thesis, University of Valle, Cali, 97pp.

Vioukov VN 1987. Control of transmission, p. 909-928. In W Peters, R Killick-Kendrick (eds). The Leishmaniases in Biology and Medicine. Vol. II. Academic Press, London.

Warburg A, Montoya-Lenna J, JaramiIlo C, Cruz-Ruiz AL, Ostrovska K 1991. Leishmaniasis vector potential of Latzomyia spp. in Colombian coffee plantations. Med Vet Entomol 5:9-16

Copyright 1995 Fundacao Oswaldo Cruz

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