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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
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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.
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Copyright 1995 Fundacao Oswaldo Cruz
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