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Memórias do Instituto Oswaldo Cruz
Fundação Oswaldo Cruz, Fiocruz
ISSN: 1678-8060 EISSN: 1678-8060
Vol. 90, Num. 2, 1995, pp. 191-194
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Memorias Instituto Oswaldo Cruz, Vol. 90(2):191-194
mar./apr. 1995
Effect of Niclosamide (Bayluscide WP 70 R),
Anacardium occidentale Hexane Extract and
Euphorbia splendens Latex on Behavior of
Biomphalaria glabrata (Say, 1818), under Laboratory
Conditions
Pedro Jurberg /*, Otilia Sarquis, Jose Augusto A dos Santos,
Regina da Conceic o Reis Ferreira
Laboratorio de Comportamento Animal, Departamento.de Biologia,
Instituto Oswaldo Cruz, Av. Brasil 4365, 21045-900 Rio de
Janeiro, RJ, Brasil *Instituto de Psicologia, Universidade
Estadual do Rio de Janeiro, Av. S o Francisco Xavier 524,
20550-011 Rio de Janeiro, RJ, Brasil
Code Number: OC95039
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Text: 20K
No associated graphics files
[TABLES AT END OF TEXT]
The repellent effect of the molluscicides Niclosamide
(Bayluscide WP 70 R), Anacardium occidentale
and the latex of Euphorbia splendens on
Biomphalaria glabrata was observed through the
investigation of the occurrence of escape behavior among
molluscs that were exposed to dosages lower than the
LD 50.
The total number of individuals out of water among the
surviving snails in the control group provided a "Natural
Escape Index". The comparison between this total and the
total number of surviving snails in each group exposed to the
different dosages of the molluscicides after 24 hr
provided the "Molluscicide Escape Index" and the detection of
a "Repellency Range" to these snails.
The escape indexes for Niclosamide, A. occidentale
and E. splendens were 10%, 6.22% and 6.44%
respectively. Repellency occurred at the following
concentration ranges: 0.01, 0.02 and 0.03 ppm Bayluscide,
0.1, 0.2 and 0.3 ppm A. occidentale and 0.05,
0.10, 0.15 and 0.20 ppm E. splendens. The
Natural Escape Index obtained in the control group was
zero.
Key words: Biomphalaria glabrata - molluscicide -
schistosomiasis - Bayluscide - Euphorbia splendens -
Anacardium occidentale
The control of schistosomiasis transmission might be
accomplished by the reduction of the populations of vector
molluscs through the use of molluscicides. Despite being
widely employed, molluscicides have their efficacy reduced by
physicochemical conditions of the environment or by the
molluscs activities which reduce partially or completely the
contact with these substances, thus favoring their survival.
These activities were classified as protective behavior (Pieri
& Jurberg 1981a, Jurberg 1987) and among them are the
retraction of the mollusc into the shell and the movement away
from the sites treated with molluscicides.
Since Biomphalaria glabrata is capable of
responding to sub-lethal dosages of molluscicides, moving away
when exposed to these substances (Nolan et al. 1953, Etges
1963, Etges & Gilbertson 1966, Souza & Paulini 1967, Pieri &
Jurberg 1981b, Jurberg et al. 1985, 1988) and since one does
not know this species behavior when in contact with
molluscicides of plant origin that might be highly promising,
such as Anacardium occidentale, studied by Rey et
al. (1987) and Euphorbia splendens, studied by
Vasconcellos and Schall (1986) and Mendes et
al. (1991), the present study aims (1) to study the
repellency of these molluscicides as compared to Niclosamide,
a widely employed product and the sole commercially available
molluscicide (McCullough 1992); (2) to establish a
technique in order to determine the Molluscicide Escape Index,
the Natural Escape Index of the population and the Repellency
Range of the molluscicides, based on the occurrence of the
emigration behavior of B. glabrata.
MATERIALS AND METHODS
One thousand four hundred and seventy melanic
B. glabrata specimens were utilized, measuring 12
to 17 mm, originated from Touros, Rio Grande do Norte,
Brazil, and maintained for several generations at the
Departamento de Biologia, Instituto Oswaldo Cruz, Rio de
Janeiro, Brazil.
The molluscicides were employed in decreasing concentrations
from the LD 50, calculated in pre-experiments through a
probit analysis procedure (Finney 1971). The minimum
concentrations corresponded to those concentrations beyond
which no significant differences were detected. The employed
concentrations were (a) Niclosamide (Bayluscide WP 70 R) -
0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04,
0.05, 0.06, 0.07 and 0.08 ppm (the last one corresponding to
the LD 50); (b) A. occidentale - 0.05, 0.06, 0.07,
0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and
1.0 ppm (the last one corresponding to the LD 50);
(c) E. splendens var. hislopii - 0.025,
0.030, 0.035, 0.040, 0.045, 0.05, 0.10, 0.15, 0.20, 0.25,
0.30, 0.35, 0.40, 0.45 and 0.50 ppm (the last one
corresponding to the LD 50).
Three groups of 10 animals (n=30) were exposed to each of
the concentrations for 24 hr in 1000 ml glass vials
(exposition phase). To every tested substance corresponded a
control group of 60 molluscs kept in distilled water,
which provided the Natural Escape Index of the population
studied. At the end of this phase the molluscs found out of
the aqueous solutions were counted, washed under water and
maintained for another 24 hr in vials containing distilled
water and food (recovery phase), after which the surviving and
the dead snails were counted. The same procedure was employed
on snails that did not exhibit the emigration behavior.
The percentage of molluscs observed out of the water after
exposure to concentrations lower than the LD 50 of each
substance and which survived the recovery phase was considered
the "Molluscicide Escape Index". The percentage of snails in
the control group that were observed out of the water after
the treatment corresponding to the recovery phase of the
experimental groups and considered alive constituted the
Natural Escape Index.
The repellency range of the molluscicides was characterized by
the identification of the concentrations at which the
Molluscicide Escape Index was higher than the Natural Escape
Index.
The significance of the differences between the escape of
snails from the water at each molluscicide concentration and
at the control group or among the three groups of
10 specimens at each concentration were established by the
Fisher test (Siegel 1975). The chi-square test was employed
for pairwise comparisons involving the different
molluscicides.
During the experiment the room temperature was 25 +/- 2 C,
the lighting period consisted of 12 hr light, 12 hr
dark and the water pH was 6.5.
RESULTS
No specimen among the 180 snails in the control group
exhibited the behavior of exiting the water.
The results of the tests comparing the occurrence of the
behavior of exiting the water by B. glabrata in the
presence of the three molluscicides at the various
concentrations are listed in Tables I, II, III.
Snails exited the water at all Niclosamide concentrations
tested. However, the occurrence of this behavior was
statistically significant only at three of these
concentrations (0.01 ppm: p=0.0023; 0.02 ppm: p=0.026;
0.03 ppm: p=0.026) p < 0.05. The Molluscicide
Escape Index was 10%.
Snails did not exit the water at all E. splendens
concentrations. However, at four of them the occurrence of
this behavior was statistically significant (0.05 ppm:
p=0.012; 0.010 ppm: p=0.026; 0.15 ppm: p=0.026 and
0.20 ppm: p=0.026) p < 0.05. The Molluscicide
Escape Index was 6.44%.
Snail exits from the water were observed at practically every
concentration of A. occidentale. However, the
difference between the number of animals which exited the
solution and those which did not was statistically significant
at the concentrations of 0.1 ppm: p=0.26; 0.2 ppm:
p=0.026; 0.3 ppm: p=0.12 p < 0.05. The
Molluscicide Escape Index was 6.22%.
A significant difference was detected between the total number
of escape instances under Niclosamide and under
A. occidentale (x^2=4.07; p<0.05). No
significant difference in the total number of escape instances
was detected under the treatments with Niclosamide and
E. splendens (x^2=3.52; p>0.05).
DISCUSSION AND CONCLUSION
The present results provide an estimate of the number of
snails that might escape the action of molluscicides, which
may be used in planning snail control with molluscicides.
Since these molluscs are prolific, hermaphroditic and able to
carry out self-fertilization, and considering the present data
and further knowledge on population ecology of planorbids, it
is possible to estimate the time taken for them to repopulate
their breeding sites, and consequently, the necessary
periodicity of the application of the product.
The results also provide data about (1) the concentrations
lower than the LD 50 at which the exiting behavior is
exhibited, which favors survival (Molluscicide Escape Index);
(2) the concentration at which the molluscicides are
repellent (Repellency Range); (3) the number of snails
that naturally exit the water, thus being able to avoid the
action of molluscicides applied to the water (Natural Escape
Index).
The behavior of exiting the water is a common phenomenon among
planorbids and it may occur due to the following factors:
(1) unfavorable conditions of the environment
(overpopulation, lack of food or dissolved oxygen, high
temperature or eutrophication of the water)
(Paraense 1957). These factors may happen isolated or in
association (Green et al. 1992); (2) in lamellate
populations, due to genetic factors (Paraense 1957,
Richards 1968) or induced by low temperatures on juvenile
snails (Pieri & Thomas 1986, Dannemann & Pieri 1991);
(3) through the repellent action of the molluscicides.
Nolan et al. (1953) observed this kind of response in
relation to the action of phenolic compounds in the
laboratory, and Rey (1973) observed the same kind of
response with sodium pentachlorophenate under field
conditions.
Based on the repellency of molluscicides Jurberg et
al. (1985) proposed the Exit Index, which consisted of the
comparison between the percentage of snails that exited the
water in the control group, without molluscicide, and the
percentage of snails that exited the water at the various
molluscicide concentrations after 24 hr. Subsequently,
Jurberg et al. (1988) verified, through cinematographic
recordings, that the snails that exited the water and remained
longer away from the Phytolacca dodecandra
concentrations had their survival favored.
The Molluscicide Escape Index adopted in the present study has
some advantages over the Exit Index. Firstly, only
molluscicide concentrations below the LD 50 are
considered, as above it lethality increases and snails no
longer exit the water. Secondly, it is easier to detect it
because only those snails are counted, which remain alive out
of the molluscicide solutions after 24 hr of test.
The three molluscicides present concentration ranges at which
they are repellent, although only in the group exposed to
Bayluscide did snails exit the water at all concentrations,
indicating repellency to some specimens even at low
concentrations.
The results obtained with distilled water showed that the
population tested did not exhibit a Natural Escape Index under
laboratory conditions.
A relevant fact is the high frequency of natural exits from
the water, recorded in some populations (Etges &
Gilbertson 1966, Pieri & Jurberg 1981b), which may
mask the repellent effect of a molluscicide. In the present
study, as new molluscicide substances are involved, it would
be profitable to test them on laboratory-bred
B. glabrata populations that exhibit this behavior
at a low frequency. Nevertheless, it must be stressed that if
the objective of a study is to determine the action mode of a
known molluscicide on a population in the field, then a sample
of this population should be utilized. The control group will
reveal, through the Natural Escape Index, if this population
is characterized by a high frequency of exits from the water.
This will be an important factor in planning a control
campaign, as it will include an estimate of that part of the
population which will not be exposed to the molluscicide due
to the above mentioned behavior.
TABLE I
Results of the comparisons done through the Fisher test
belween the percentage ofBiomphalaria glabrata snails
exiting the water in the presence of Niclosamide
(Bayluscide WP 70 R n=30 in each concentration) and
the percentage of snails exiting the water in the control
group. The escape behavior was not observed m the
control group (ns: not significant)
Concentration Escape Fisher test
(ppm) (%)
0.005 6.7 ns
0.006 10 ns
0.007 10 ns
0.008 10 ns
0.009 10 ns
0.01 26.7 p<0.01
0.02 16.7 p<0.05
0.03 16.7 p<0.05
0.04 10 ns
0.05 3.3 ns
0.06 3.3 ns
0.07 3.3 ns
0.08 3.3 ns
TABLE II
Results of the comparisons done through the Fisher
test between the percentage of Biomphalaria glabrata
snail exiting the water in the presence of Anacardium
occidentale (n=30 in each concentration) and the
percentage of snails exiting the water in the control group.
The escape behavior was not observed in the control group
(ns: not significant)
Concentration Escape Fisher test (ppm)
(%)
-------------------------------------------
0.05 0 ns
0.06 3.3 ns
0.07 3.3 ns
0.08 3.3 ns
0.09 6.7 ns
0.1 16.7 p< 0.05
0.2 16.7 p< 0.05
0.3 20 p< 0.05
0.4 10 ns
0.5 6.7 ns
0.6 3.3 ns
0.7 3.3 ns
0.8 0 ns
0.9 0 ns
1.0 0 ns
TABLE III
Results of the comparisons done through the Fisher
test between the percentage of Biomphalaria glabrata
snails exiting the water in the presence of Euphorbia
splendens (n:30 in each concentration) and the percentage
of snails exiting the water in the control group. The
escape behavior was not observed in the control group
(ns: not significant)
Concentration Escape Fisher test (ppm)
(%)
---------------------------------------------------
0.025 0 ns
0.030 3.3 ns
0.035 0 ns
0.040 3.3 ns
0,045 3.3 ns
0.05 20 p<0.05
0.10 16.7 p<0.05
0.15 16.7 p<0.05
0.20 16.7 p<0.05
0.25 10 ns
0.30 6.7 ns
0.35 3.3 ns
0.40 0 ns
0.45 0 ns
0.50 0 ns
ACKNOWLEDGEMENTS
To Otavio Pieri, Marisa Soares and Marli Maria Lima for the
critical reading of the manuscript and the suggestions
given.
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Copyright 1995 Fundacao Oswaldo Cruz (Fiocruz)
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