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Memórias do Instituto Oswaldo Cruz
Fundação Oswaldo Cruz, Fiocruz
ISSN: 1678-8060 EISSN: 1678-8060
Vol. 89, Num. 2, 1994, pp. 247-250
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Mem. Inst. Oswaldo Cruz, Rio de Janeiro, Vol. 89(2):
247-250, apr./jun. 1994
Thevetia peruviana (Family: Apocynaceae) in the Control of
Slug and Snails Pests
A Panigrahi, SK Raut
Code Number: OC94051
Size of Files:
Text: 20K
No associated graphics files
Ecology and Ethology Laboratory, Department of Zoology, University
of Calcutta, 35 Ballygunge Circular Road, Calcutta 700 019, India
An aqueous extract prepared from Kernels of the fruit of
Thevetia peruviana (Pers.) Schumann (Family : Apocynaceae)
was found under experimental conditions, to be toxic to the slug
Laevicaulis alte (Ferussac) and the snail Achatina fulica
Bowdich, the important agrihorticultural pests of Indo-Pacific
countries. Concentrations as low as 1% (w/v) killed all the slugs
exposed in less than 981.00 (+/- SD 22.76) min, and 2% of the
extract killed 100% of the slugs L. alte and 50%, 50% and
30% of the snail A. fulica in between 92.34 (+/- SD 6.63) -
321.33 (+/- SD 4.14) and 271.20 (+/- SD 17.54) - 298.26 (+/- SD
16.69) min respectively. The most effective concentration of the
extract was 20%; it killed 100% of exposed slugs and snails within a
short time (40-50 and 90-1440 min respectively) when the extract was
exposed on the soil in experimental trays or when it was applied to
potato slices offered as food to the gastropods.
Key words: Thevetia peruviana - fruit kernel extract - pest
control - slugs - snails
The slug Laevicaulis alte (Ferussac) and the snail
Achatina fulica Bowdich are serious agrihorticultural pests
in most of the Indo-Pacific countries. Various attempts to control
them have failed. Although some synthetic molluscicides are giving
encouraging results (Godan 1983, Henderson 1989, Panigrahi &
Raut 1993), their use in being discouraged because of their
potential harmful effects to the environment. Naturally occuring
molluscicides on the other hand, are considered relatively safe to
the environment. Whereas reports on the use of natural products in
the control of freshwater snails are available (Baalarwy 1972, Godan
1983, Singh & Agarwal 1984, 1987, Cruz-Reyes et al. 1989, Mendes
et al. 1992), information on the use of these products to control
terrestrial molluscs is limited (Thomas 1948). In the present
programme an attempt has been made to study the toxicity of the
fruit of Thevetia peruviana (Pers.) Schumann (Family:
Apocynaceae) to the molluscan pests, L. alte and A.
fulica, under experimental conditions.
MATERIALS AND METHODS
Ripe T. peruviana fruits were collected from the local
gardens. Kernels removed from these were then ground and the
resulting paste was used to prepare aqueous suspensions of the
extract at the following concentrations: 100%, 50%, 25%, 20%, 10%,
5%, 2% and 1%. For the concentration of 100%, the paste was used
undiluted. Lower concentrations were prepared in water from weighed
quantities of the paste. The test substance was either sprayed on to
the target molluscs or was offered as bait to the organisms.
The test animals of L. alte or A. fulica collected
from a local vegetable garden were divided into three groups: 20.0 -
22.5mm, 40.3 - 42.5mm, and 66.2 - 68.2mm body length of L.
alte and 23.5 - 25.2mm, 45.0 - 48.4mm, and 62.2 - 64.0mm shell
lenght of A. fulica, of around 1, 3 and 6 months old. The
three groups of each species were kept in separate terraria under
laboratory conditions. Each terrarium was provided with a substratum
of loose, moist soil, about 4 cm thick. The animals were fed on
lettuce, gourd or marigold leaves regularly.
The experiments were conducted in enamel trays, each measuring 40 x
30 x 6 cm, and one tray was used for one test concentration. Each
tray was provided with a substratum of loose, moist soil, 2 cm
thick. The test suspension at the appropriate concentration was
sprayed on to the soil substratum matter. An hour later the animals
were introduced into the trays, and each tray received 30 (10 from
each size group) individuals of either L. alte or A.
fulica. In other trays of same specifications but free from
application of T. peruviana extract, L. alte and A.
fulica of same number of each size group were introduced for
control experiment. All the animals were supplied with food ad
libitum. Each experiment was repeated thrice.
For bait experiments, potato slice (2 mm thick) were used. The
potato slice were sun dried for a period of 6-8 hr, and then
"soaked" for 1 hr in the extract of T. peruviana. The slices
were then offered to the slugs or snails kept in terraria measuring
45x25x15 cm in size. The animals were also given excess additional
food in the form of lettuce, gourd or marigold leaves. Each
terrarium was covered with a piece of nylon net (mesh size 0.25mm)
to prevent escape of the animals. Each experiment was repeated three
times and the data on the time (in minutes) taken to arrest foot
muscle movement and to death of exposed animals as well as the
percentage of animals killed were recorded carefully to calculate
the mean value. Goon et al. (1976) was consulted for statistical
analysis.
RESULTS
The slug L. alte and the snail A. fulica when in
contact with the extract of T. peruviana behaved differently
with repect to the concentrations used. On coming into contact with
the extract of T. peruviana sprayed and soil surface the
slugs increased their movement but within 3-7 min they slowed down
and became imobile. Their foot-muscles contracted at regular
intervals, and at this stage the animals started screting mucus. The
anterior part of the body moved convulsively, and was frequently
lifted above the soil surface. Small, rapid waves of contraction ran
through the skin musculature. Finally, muscular contractions became
less, and the head was withdrawn permanently. The time taken to
arrest foot muscle movements or death in slugs exposed to the
extract varied with respect to age of the individuals and the
concentrations of the extract (Table I). At a concentration of 100%
T. peruviana extract produced 100% mortality in 20.0 - 22.5
mm size group, and 80% mortality in the 40.3 - 42.5mm and 66.2 -
68.2mm L. alte. T. peruviana extract at a
concentration of 1% (w/v) did not produce a noticeable effect on the
activity of the giant land snail A. fulica even after three
days of exposure, and no mortality occured at this concentration
(Table I). However, at a concentration of 2% (w/v) or above the
snails were seen to withdraw the tentacles and head within 5-10 min.
This was followed by complete retraction of the body into the shell.
The animals, in the meantime produced mucus continuously. Snails
were considered dead when mucus released ceased. The highest
concentration of the extract (100%) produced on average 60%, 50%,
30% mortality and 2% of the extract produced 50%, 50%, 30% mortality
in the 23.5 - 25.2mm, 45.0 - 48.4mm and 62.2 - 64.0mm A.
fulica respectively. All the other concentrations produced 100%
mortality in the snails.
TABLE
Time in minutes (mean +/- SD) taken to arrest foot muscle
movement or to cause death in the slug Laevicaulis alte
and snail Achatina fulica after application of
different concentrations of Thevetia peruviana extract.
[A total of ten individual (in each experiment) were exposed
to each concentration of the extract. Each experiment was
repeated thrice and a total of 10 x 3 - 30 individuals were
exposed]
======================================================================
Mollusc Concentrations Time taken to arrest foot movement in
species used of -----------------------------------------------
extract 1 month old 3 months old 6 months old
(% w/v) gastropods gastropods gastropods
----------------------------------------------------------------------
Laevicaulis 100 23.97(+/-2.16) 28.30(+/-3.12) 47.50(+/-5.59)
alte 50 9.34(+/-1.11) 16.67(+/-1.89) 21.00(+/-0.82)
25 5.77(+/-0.85) 16.00(+/-0.82) 13.77(+/-1.15)
20 4.84(+/-0.69) 14.17(+/-2.27) 11.04(+/-1.14)
10 15.10(+/-1.47) 18.34(+/-1.11) 13.07(+/-1.94)
5 43.43(+/-3.25) 55.04(+/-3.44) 42.00(+/-1.91)
2 71.53(+/-10.77) 78.00(+/-7.83) 31.83(+/-2.86)
1 77.96(+/-7.84) 83.50(+/-2.29) 90.21(+/-3.25)
Achatina 100 55.17(+/-3.24) 77.90(+/-5.49) 97.57(+/-4.85)
fulica 50 27.50(+/-2.63) 27.00(+/-4.53) 28.44(+/-3.65)
25 16.16(+/-1.06) 17.16(+/-2.33) 16.74(+/-1.88)
20 12.67(+/-2.58) 12.17(+/-1.96) 16.87(+/-1.75)
10 17.54(+/-2.02) 17.44(+/-1.97) 14.50(+/-1.39)
5 34.23(+/-3.05) 60.83(+/-4.45) 68.04(+/-6.43)
2 64.70(+/-5.12) 79.50(+/-7.20) 104.50(+/-9.31)
1 a a a
----------------------------------------------------------------------
Mollusc Concentrations Time taken to death of the exposed
individuals in
species used of -------------------------------------------------
extract 1 month old 3 months old 6 months old
(% w/v) gastropods gastropods gastropods
------------------------------------------------------------------------
Laevicaulis 100 37.30(+/-1.90) 58.20(+/-1.73) 77.10(+/-2.42)
alte 50 44.63(+/-4.51) 80.23(+/-11.36) 85.14(+/-8.42)
25 37.00(+/-1.92) 54.83(+/-3.57) 62.83(+/-9.74)
20 35.09(+/-3.89) 43.40(+/-3.00) 46.27(+/-6.65)
10 58.24(+/-4.66) 51.70(+/-1.95) 68.27(+/-4.20)
5 65.13(+/-3.28) 70.89(+/-6.31) 256.06(+/-10.36)
2 92.34(+/-6.63) 136.62(+/-10.39) 321.33(+/-4.14)
1 870.34(+/-29.82) 883.77(+/-27.82) 981.00(+/-22.76)
Achatina 100 137.67(+/-9.56) 324.20(+/-18.63) 457.24(+/-18.09)
fulica 50 138.80(+/-8.82) 317.64(+/-9.76) 913.54(+/-23.11)
25 118.00(+/-6.11) 162.07(+/-4.90) 187.17(+/-3.03)
20 84.66(+/3.34) 128.63(+/-5.64) 127.80(+/-5.89)
10 78.00(+/-1.63) 94.00(+/-4.24) 173.80(+/-6.36)
5 271.20(+/-17.54) 305.53(+/-16.60) 298.26(+/-16.69)
2 1059.80(+/-17.52)1054.60(+/-20.85)1053.10(+/-20.79)
1 - - -
=========================================================================
a: not effective
- : no death
TABLE II
Results of ANOVA and 't' test in respect to the
effectiveness of Thevetia peruviana
=================================================
Factor Fcal Ftab p-value
-------------------------------------------------
Age gourp 4.74 3.74 0.05
Pest species 13.51 4.60 0.05
Concentrations (%)
used 16.59 2.77 0.05
Concentrations (%)
x pest species 27.24 2.77 0.05
Age x pest species 0.64 3.74 0.05
Age x concentrations
(%) used 0.51 2.498 0.05
=================================================
Potato slices treated with different concentrations of T.
peruviana were readily accepted by the slugs or snails.
Irrespective of concentrations of T. peruviana, individuals
that consumed the potato slices died. Within 5-20 min of consuming
the bait the slugs and snails became immobilised, and produced mucus
profusely. The snails retracted into their shells. The slugs, on the
other hand, initially produced foot-muscle contractions which were
followed by rapid contractions of body musculature. Finally, the
body contracted and the individual died. Usually the slugs died
within 40-50 min whereas the snails died within 90-1440 min.
In most cases, the snout of the snail was pushed out of the shell
aperture at the time of death. In some cases the oesophagus was
everted out of the mouth of the affected gastropods just prior to
death.
To justify the validity of the data obtained in respect to different
age groups, concentrations (%) of T. peruviana used and time
taken for death of the slugs and snails the two-way fixed effect
homoscedastic Analysis of Variance (ANOVA) and Student's `t' test
were applied. From the results it is clear that there exists
significant difference among the different age groups of slugs (Fcal
= 6.44, Ftab = 2.74, p = 0.05) and the effect is maximum in three
months age group. Also, there exists significant difference among
different concentrations (%) of T. peruviana used to kill the
slugs (Fcal = 112.86, Ftab = 2.77, p = 0.05). The threshold
concentrations are 1% and 20%. In A. fulica the effect of the
age though not significant (Fcal = 2.911, Ftab = 3.88) there exists
significant differences among different concentrations of T.
peruviana (Fcal = 15.14, Ftab = 3.00, p = 0.05). The threshold
concentrations are 2% and 20%. As regards to the effectiveness of
T. peruviana doses it is evident that there exists
significant influence of the gastropods, the species of the
gastropods and the joint interaction of the concentrations and
species (Table II). The tresholds levels of significant interactions
are 2% for A. fulica and 20% for L. alte.
DISCUSSION
The present study indicates that the extract from kernels of T.
peruviana fruit is toxic to terrestrial slugs and snails, and
promises to be effective in the control of these moluscs.
Since 100% mortality has been recorded in both L. alte and
A. fulica following application of 50%, 25%, 20%, 10% and 5%
concentrations of T. peruviana kernel extract, it is clear
that such concentrations are equally effective for both the
gastropods species. The variations noted in mortality rates of L.
alte and A. fulica in respect to application of 100%
concentration of T. peruviana are most probably related with
the defensive mechanism of the individuals of the mollusc species
concerned. It is obvious that the slugs and snails, inviariably
released a large amount of mucus following application of the
molluscicide. Since 100% concentration of T. peruviana is
very thick and the slugs and snails started releasing mucus soon
after they came in contact with the extract a thick mucoid barrier
is produced in between body surface and the extract materials. Such
a barrier prevents further contact of the body surface with the
toxic matter. Depending upon the degree of reaction in respect to
the amount of extract the animal absorbed at the first touch, the
assurance of survival is determined. It is most likely that the
slugs of smallest size group (20.0 - 22.5mm in body length) are not
capable to overcome the toxic reaction following first touch. But,
it is likely that some of the individuals belonged to two next
higher size groups (40.3 - 42.5mm and 66.2 - 68.2mm in body length)
of L.alte and all the three size groups of A. fulica
are able to overcome the toxic hazards and are survived. It is
evident that L. alte and A. fulica exposed to
different effective concentrations of T. peruviana responded
differently in respect to time. As regards to 50%, 50% and 30%
mortalities in 23.5 - 25.2mm, 45.0 - 48.4mm and 62.2 - 64.0mm size
groups of A. fulica at 20% concentration and no death at 1%
concentration contrast to 100% mortality at these concentrations, in
L. alte it is sure that 1% concentration of T.
peruviana is not at all effective and 2% concentrations is
effective, to some extent, to kill A. fulica belonged to
different size groups. This suggests that the molluscicides, of
course, at lower concentrations act differently in respect to the
withstanding power of the species and the individuals of the species
concerned.
Since these molluscs are nocturnal and remain active almost
throughout the night (10-12 hr) it is no matter how quickly they
could be killed during the nigh hours. Rather, it is desirable to
ensure their death during one night-hour through the use of minimum
extract of T. peruviana. For these reasons, it would be wise
to apply 1% concentration and 5% concentration of T.
peruviana respectively against L. alte and A.
fulica occuring separately in different gardens, and only 5%
concentration of the extract if those two gastropod pests are
occurring in the same garden.
ACKNOWLEDGEMENT
To the Head of the Department of Zoology, University of Calcutta for
facilities provided.
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Copyright 1994 Fundacao Oswaldo Cruz - FIOCRUZ
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