Table Of Content©
SociedadEspañoladeMalacología Iberus, 19 (1): 65-73, 2001
Environmentally safe moUuscicides from two common eu-
phorbiales
Molusquicidas no perjudiciales para el medioambiente obtenidos a
partir de dos euforbiáceas
Ram P. YADAV* andAjay SINGH*'
Recibidoel15-V-2000.Aceptadoel14-1I1-2001
ABSTRACT
Aqueous extracts of látex and stem bark of Codiaeum variegatum and Crotón tiglium (Eup-
horbiaceae) have a high molluscicidal activity. It was observed that the molluscicidal acti-
vityofextracts of both the plants againsttwo harmful fresfiwater snails Lymnaea acuminata
and Indoplanorbis exustus was time as well as dose dependent. There was a significant
negative correlation between LC50 valúes and exposure periods thus increase in exposure
time, the LC50 of Crotón tiglium and Codiaeum variegatum lotices were decreased from
O.OóO mg DW/L (24h)> to 0.014 mg DW/L (9óh) and 0.381 mg DW/L (24h)> to
0.159 mg DW/L (96h), respectively ogoinst Lymnaea acuminata and 0.034 mg DW/L
(24h)> to 0.009 mg DW/L (96h) and 0.246 mg DW/L (24h)> to 0.030 mg DW/L (96h),
respectivelyagainst Indoplanorbis exustus.
These plant part extracts at higher doses were olso lethol to freshwoter fish Channa punc-
tatus, which shores the habitat with these snails, but the doses LC90, (24h) of snails are
safe for fish.
RESUMEN
Los extractos acuosos de látex y corteza del tallo de Codiaeum variegatum y Crotón
tiglium (Euphorbioceae) tienen una alta actividad molusquicida. Esto actividad, frente a
dos caracoles de aguo dulce dañinos, Lymnaea acuminata y Indoplanorbis exustus
,
depende tanto del tiempo como de la dosis. Hoy uno correlación negativa significativa
entre los valores LC50 y los periodos de exposición según se aumentan éstos, el LC50 de
los látex de Crotón tiglium y Codiaeum variegatum fueron decrecientes 0.060 mg DW/L
(24h)> hasta 0.014 mg DW/L (96h) y 0.381 mg DW/L (24h)> hasta 0.159 mg DW/L
(9óh), respectivamente contra Lymnaea acuminata y 0.034 mg DW/L (24h)> hasta
0.009 mg DW/L (96h) y 0.246 mg DW/L (24h)> desde 0.030 mg DW/L (96h), respec-
tivamente contra Indoplanorbis exustus.
Estos extractos de partes de plantos o dosis mayores fueron también letales para el pez
de agua dulce Channa punctatus, que comparte habitat con estos dos caracoles, pero la
dosis LC90, (24h) ero inocua para los peces.
KEYWORDS:Molluscicide, Codiaeumvariegatum. Crotóntiglium, Lymnaeaacuminata, Indoplanorbisexustus,
Euphorbiaceae.
PALABRAS CLAVE: Molusquicida, Codiaeum variegatum. Crotón tiglium, Lymnaeaacuminata, Indoplanorbis
exustus, Euphorbiaceae.
*DepartmentofZoology, D.D.U. GorakhpurUniversity, Gorakhpur-273009 U.P. INDIA
'Authortowhomcorrespondenceshouidbemade.
65
Iberus, 19 (1), 2001
INTRODUCTION
Recent studies have indicated that versity, Gorakhpur and identified by
there are a number of medicinal plants Prof. S.K. Singh (taxonomist), Botany
which may be useful for control of snail Department, D.D.U. Gorakhpur Univer-
population and henee control transmis- sity, Gorakhpur.
sion of schistosomiasis and fascioliasis
(Medina and Ritchi, 1980; Marston Preparation of aqueous extracts of
AND Hostettman, 1987; Gopalsamy, StembarkandLátex
GUEHO, JULIEN, OWADALLY AND HOS- Stem bark: The fresh stem bark
TETTMAN, 1990; SlNGH, SlNGH AND (50mg/5ml) were minced with distilled
SlNGH, 1996; SlNGH AND SlNGH, 1997; water homogenized for 5 min and cen-
SuKUMARAN, Prashar AND Rao, 1994; trifuged at 1000 g for 10 minThe super-
Marston, Dudan, Gupta, Salís, natant was used as a water extract for
CorreaANDHostettman, 1996;Geerts, themolluscicidalactivity.
Alard, Belot and Sidhom, 1992; Látex: The white látex from these
Amusan, Msothi and Makhuba, 1997 plants was drained in glass tubes by
and Laurens, Fournean, Hoaqnemi- cutting their stem ápices, this látex was
ller,Care,BoriesandLoiseau, 1997). lyophilized at - 40 °C and lyophilized
Molluscicides derived from plants powder was stored for further use. The
that can be grown in endemic áreas of freeze-dried powder was mixed with
fascioliasis transmission may provide a appropriate volume of distilled water to
relatively low costmeans for controUing obtain the desired concentrations. The
snail intermedíate hosts, since expenses wet weight of volume of 1 mi látex of
of synthesis, marketing and transporta- Codiaeum variegatum and Crotón tiglium
tion are reduced or eliminated. But, the was 810 mg and 800 mg respectively
use of plant products as molluscicides and dry weight was 305 mg and 300 mg
would be justified only, if it can be respectively.
demonstrated that the effect of the dose Lymnaea acuminata (2.6±0.3 cm in
needed as molluscicide is non-toxic to shell height), Indoplanorbis exustus
otheraquaticanimáis, especiallyfish. (0.87±0.035 cm in shell height) and
The present study reports the Channa punctatus (10.5±0.9 cm in total
molluscicidal effect of the two euphor- length) were collected from Ramgarh
biousplantsi.e. Codiaeumvariegatum and Lake of Gorakhpur district, and used as
Crotón tiglium (whichisa commonly cul- test animáis. Toxicity experiments were
tivated as an ornamental plant in performed using the method of Singh
gardens, and is usually called a Crotón) and Agarwal (1988). Ten experimental
against the harmful snails Lymnaea acu- animáis were kept in glass aquaria, con-
minata and Indoplanorbis exustus. These taining3Lofdechlorinatedtapwaterfor
snails are vectors of liver fluke, Fasciola both the snails. The experimental ani-
hepática and Fasciola gigantica, which máiswereexposed continuously for96h
causes endemic fascioliasis in Eastern to four different concentrations. Control
Uttar Pradesh (SlNGH and Agarwal, animáis were kept under similar condi-
1981). Toxicity experiments have also tionswithoutanytreatment.
carried out on freshwater fish Channa Toxic effect of aqueous extracts of
punctatus (which shares the habitat with látex and stem bark of both the plants
snails)forenvironmentaltoxicity,ifany. was also studied in mixed populations
of fish and snails. In these experiments,
a group of 10 snails Lymnaea acuminata
MATERIALSAND METHODS and 10 fish Channa punctatus were put
together in 6L dechlorinated tap water.
Látex and stembarkofboththeeup- These mixed populations were exposed
horbiales were collected from the Bota- to previously determined LC90 (24h) of
nical garden ofD.D.U. Gorakhpur Uni- snailsfor24h.
66
Yadavand SinGH: Environmentallysafemolluscicides from two common euphorbiales
Table I. Toxicity (LCIO, 50, 90) ofaqueous freeze-dried látex extracts of Crotón tiglium (Family
Euphorbiaceae) against Lymnaea acuminataat different time intervals. Batches often snails were
exposed to fourdifferentconcentrationsofaqueous extracts oflátexofCrotón tiglium. Concentra-
tions (Dryweight oflátex) given are the final concentrationsW/V in aquarium water. Regression
coefiPicient showed that there was significant (P<0.05) negative regression between exposure time
anddifferentLCvalúes. LCL: lowerconfidencelimit. UCL: upperconfidencelimit.Therewas no
mortalityincontrolgroups.
TablaI. Toxicidaddeextractosacuososliofilizadosdelátex(LCIO, 50, 90)deCrotóntiglium (Familia
Euphorbiaceae)frenteaLymnaeaacuminata endiferentesintervalosdetiempo. Gruposde 10caracoles
fueronexpuestosa4diferentesconcentracionesdeextractosacuososdelátexdeCrotóntiglium. Lascon-
centraciones indicadas (peso seco de látex) son concentracionesfinalesP/Ven elagua delacuario. Los
coeficienesderegresión muestranquehayregresionesnegativassignificativas (P<0.05)entreeltiempode
exposiciónydiferentes valoresdeLC. LCL: limite inferiorde confianza. UCL: limitesuperiorde con-
fianza. Nohubomortalidadenlosgruposdecontrol
Effecfive Limit
Exposure dose(W/V) (mgDW/L) Slopevalué '\'ratio 'g'valué Heterogeneify
periods (mgDW/L) LCL UCL
24h LCl0=0.015 0.011 0.017
LC50=0.06 0.03 0.07 3.98+0.78 5.05 0.15 0.22
LC90=0.19 0.14 0.42
48h LC10=0.0n 0.005 0.013
LC50=0.04 0.03 0.06 2.17±0.56 3.86 0.57 0.22
LC90=0.15 0.07 0.31
72h LCl0=0.007 0.004 0.01
LC50=0.02 0.017 0.025 2.69±0.50 5.36 0.13 0.77
LC90=0.0ól 0.043 0.13
96h LCl0=0.04 0.002 0.006
LC50=0.014 0.012 0.017 2.38±0.47 4.99 0.15 0.30
LC90=0.05 0.036 0.106
Mortality was recorded at24h inter- 30.5-31.5 °C and 27.0 -28.0 °C, respec-
vals up to 96h. Lethal concentrations tively. pH of water was 7.3 - 7.5, while
(LCIO, 50, 90)valúes, Upper and Lower dissolved oxygen, free carbón dioxide
confidence limits (UCL, LCL) and slope and bicarbonate alkalinity were ranging
valúes were calculatedby the Probit log from 6.8-7.6, 4.4-6.5 and 105.0- 109.0
method using POLO computer pro- mg/L, respectively for whole experi-
gramme of Russell et al. (1977). The ments.
regression coefficient was determined
between exposure time and different (A) Effects on Behavioural changas
valúesofLC50(SoKALandRohlf, 1973). andPoisoningSymptoms
Exposure to the aqueous extracts of
látex and stembark ofCodiaeum variega-
RESULTS tum and Crotón tiglium caused signifi-
cant behavioural changes in the fresh-
Experimental conditions of water water snails Lymnaea acuminata and
determined by the method of Indoplanorbis exustus. Behavioural
APHA/WPCF (1980). Atmospheric and changes appear with 5 to 10 min of
water temperature was ranging from exposure. The initial 30 - 45 min was a
67
. .
Iberus, 19 (1), 2001
Table 11. Toxicity (LCIO, 50, 90) ofaqueous freeze-dried látex extracts of Crotón tiglium (Family
Euphorbiaceae) against Indoplanorbis exustusat different time intervals. Other details are as given
inTable 1
Tabla II. Toxicidadde extractos acuosos liofilizados de látex (ICIO, 50, 90) deCrotón tiglium
(Familia Euphorbiaceae)frentea Indoplanorbis exustus en diferentes intervalos de tiempo. Resto de
detallescomoenla TablaI
Effective Limit
Exposure dose(W/V) (mgDW/L) Slopevalué 'Mratio 'g'valué Heterogeneity
periods (mgDW/L) LCL UCL
24h LCl0=0.009 0.006 0.018
LC50=0.034 0.026 0.063 2.36+0.53 4.50 0.18 0.28
LC90=0.117 0.063 0.549
48h LCl0=0.005 0.003 0.008
LC50=0.02 0.017 0.025 2.36±0.42 5.56 0.12 0.18
LC90=0.068 0.044 0.161
72h LCl0=0.004 0.002 0.006
LC50=0.015 0.012 0.017 2.42±0.40 6.04 0.10 0.26
LC90=0.050 0.035 0.095
96h LCl0=0.03 0.002 0.004
LC50=0.009 0.008 0.011 2.96±0.41 7.22 0.48 0.74
LC90=0.026 0.021 0.037
Table III. Toxicity (LClO, 50, 90) ofaqueous freeze-dried látex extracts ofCodiaeum variegatum
(Family; Euphorbiaceae) against lymnaeaacuminataatdifferenttimeintervals. Otherdetailsareas
giveninTable 1
TablaIII. Toxicidaddeextractosacuososliofilizadosdelátex(ICIO, 50, 90)deCodiaeumvariegatum
(FamiliaEuphorbiaceae)frenteaLymnaeaacuminata endiferentesintervalosdetiempo. Restodedeta-
llescomoenla TablaI.
Effective Limit
Exposure dose(W/V) (mgDW/L) Slopevalué 't'ratio 'g'valué Heterogeneity
periods (mgDW/L) LCL UCL
24h LCl0=0.159 0.108 0.189
LC50=0.381 0.321 0.546 3.41±0.77 4.42 0.19 0.39
LC90=0.906 0.600 2.589
48h LC10=0.120 0.081 0.147
LC50=0.258 0.023 0.291 3.92±0.69 5.62 0.12 0.15
LC90=0.546 0.432 0.870
72h LCl0=0.099 0.066 0.120
LC50=0.195 0.171 0.213 4.37±0.69 6.26 0.98 0.20
LC90=0.381 0.330 0.501
96h LCl0=0.090 0.060 0.117
LC50=0.159 0.141 0.171 6.60±0.93 7.08 0.07 0.69
LC90=0.246 0.228 0.279
68
.
Yadavand Singh: Environmentallysafe moUuscicides from two common euphorbiales
Table IV. Toxicity (LCIO, 50, 90) ofaqueous freeze-dried látex extracts of Codiaeum variegatum
(Family Euphorbiaceae) against Indoplanorbis exustusat different time intervals. Other details are
asgiveninTable 1
TablaIV. Toxicidaddeextractosacuososliofilizadosdelátex (LClO, 50, 90)deCodiaeumvariegatum
(Familia Euphorbiaceae)frenteaIndoplanorbis exustus en diferentes intervalos de tiempo. Resto de
detallescomoenla TablaI.
Effective Limit
Exposure dose(W/V) (mgDW/L) Slopevalué 't'ratio 'g'vaiue Heterogeneity
periods (mgDW/L) LCL UCL
24h LCl0=0.045 0.024 0.063
LC50=0.246 0.183 0.417 1.78±0.3 5.11 0.27
LC90=1.29 0.651 5.793
48h LC10=0.018 0.006 0.027
LC50=0.093 0.075 0.117 1.82±0.28 6.42 0.09 0.28
LC90=0.471 0.318 0.996
72h LCl0=0.009 0.003 0.018
LC50=0.048 0.036 0.060 1.98±0.28 6.42 0.09 0.92
LC90=0.222 0.165 0.248
96h LCl0=0.006 0.003 0.012
LC50=0.030 0.018 0.039 2.16±0.32 6.60 0.08 0.98
LC90=0.117 0.093 0.168
period of hyperactivity during which and Figure 1). Thusincreaseinexposure
slugish snails moved rapidly in the time the LC50 of Crotón tiglium látex
aquarium water. After some time they decreased from 0.06 mg DW/L (24h);>
started crawling on each other. As the 0.04 mg DW/L (48h);> 0.02 mg DW/L
poison enters in the snail'sbody, a mus- (72h);> to 0.014 mg DW/L (96h) and
cular twitching and the snails become 0.034 mg DW/L (24h);> 0.02 mg DW/L
spirally twisted, which resulted ataxia, (48h); 0.015 mg DW/L (72h);> to 0.009
convulsión, paralysis and finally death mg DW/L (96h) in case of Lymnaea acu-
of snails. Prior to death, there was com- minata and Indoplanorbis exustus, respec-
plete withdrawal of the body inside the tively (Tables I, II). Same trend of toxi-
shellthatindicatesnervepoisoning. city was observed in case of stem bark
extracts of Crotón tiglium and Codiaeum
(B) Dose-mortalityresponse variegatum against both the snails at all
LC valúes (LCIO, 50, 90) of aqueous theexposureperiods(Fig. 1).
extracts oflátex and stembark ofCrotón Laboratory experiments also indica-
tiglium and Codiaeum variegatum for tes that the látex and stem bark extracts
period ranging from 24h to 96h for the of both the plants were more toxic
snails, Lymnaea acuminata and Indopla- against Indoplanorbis exustus than
norbis exustushavebeengivenin (Tables Lymnaea acuminata at all the exposure
I-IV and Figure 1). In case of both the periods.
snails toxicity was time as well as dose At higher dose, active moiety of
dependent. There was a significant plants, which were effective against the
negative correlation between LC50 snails, would also cause death amongst
valúes and exposure time (Tables I-IV the fish. Consequently, a mixed popula-
69
Iberus, 19 (1), 2001
Table V. Per cent mortality (mean ±SE) ofLymnaea acuminataand Channapunctatuscaused by
aqueous extracts oflátex and stem bark (i.e. 24h LC90 ofsnail) of Codiaeum variegatum and
Crotón tiglium after 24h exposure period. Each aquarium contained ten fish {Channapunctatus)
and ten snails {Lymnaeaacuminata) in 6Ldechlorinated tapwater.Therewas no mortalityin case
ofcontrolgroup.
Table V.Porcentajede mortalidad(media ±SE) deLymnaea acuminatayChanna punctatusprodu-
cidaporextractosacuososdelátexycortezadetallos(i.e. 24hLC90decaracoles)deCodiaeumvariega-
tumyCrotón tiglium después de24horas de exposición. Cada acuario contenia 10peces (Channa
punctatus^j 10caracoles (Lymnaea acuminata^ en 61deaguadegrifodesclorada. No hubo mortali-
dadenelgrupodecontrol
Experimental Concentration %
Plants PlantParts Mortality
animáis (mgDW/L)(w/v)
Codiaeum variegatum Látex L. acuminata 0.906 (LC90) 91.6±2.31
C. punctatus Zero
Stem bark L. acuminata 50.14 (LC90) 93.3±1.15
C. punctatus Zero
Crotón tiglium Látex L. acuminata 0.19 (LC90) 100
C. punctatus Zero
Stem bark L. acuminata 35.52 (LC90) 95.0±2.45
C. punctatus - Zero
tions of 10 snails {Lymnaea acuminata) of thesebehavioural responses indicates
and 10 fish {Channa punctatus) were that, the látex perhaps contains some
treated with the 24h, LC90 of látex and neurotoxins, which amongst other
stem bark of Crotón tiglium and Codia- think, might be active at the neuromus-
eum variegatum, upto theLC90 doses for cular system of the exposed animáis.
snail Lymnaea acuminata there was no Similar behavioural responses were also
mortalityamongstfish(TableV). observed Singh and Agarwal (1990),
The slope valúes given in toxicity in their study on acute toxicity oflatices
tables (I - IV) were steep and heteroge- ofEuphorbia royleana, Euphorbia antisyph-
neity factor was less than 1.0 indicates liatica and ]atropha gossypifolia on snail
the result found to be within the 95% Lymnaea acuminata. The behavioural
confidence limits of LC valúes. The changes are indeed reminiscent to the
regression test ('t' ratio) was greater response of snails to organophosphorus
than 1.96 and the potency estimation and carbamate pesticides (Singh and
test Cg' valué) was less than 0.5 at all Agarwal, 1981).
probabilitylevéis. No such behavioural symptoms and
death occurred in control groups indica-
ting that no factor other than plant
DISCUSSION moieties was responsible for altered
behaviourandmortality.
Data ofpresentstudy shows thatthe Mortality caused by the plant parts
extracts ofboth the plants caused signi- preparation showed a clear significant
ficant behavioural changes in both the positive correlation between dose and
freshwater snails. The most obvious mortality. For example, for látex of
signofdistressinthetreated snailswere Crotón tiglium present mortality of snail
muscular twitching and spiral twisting Lymnaea acuminata after 24h was 10% at
of the body, followed by crawling on 0.015 mg DW/L which increased up to
each other. The nature and rapid onset 90% at 0.004 mg DW/L (Table I) which
70
Yadavand SinGH: Environmentallysafe molluscicides from two common euphorbiales
3,5-, "
Crotóntiglium
3-
1 [ Codiaeumvariegatum
2,5
0,8
2
0,6-
1,5H
0,4-
1
0,5- 0,2- n
48h 96h
Figure 1. Bar diagram showing the toxicity (LC50; ml/1) ofaqueous stem bark extraer of Crotón
tigliumand Codiaeum variegatumagainst Lymnaeaacuminata (A) and Indoplanorbis exustus(B) at
difFerent time intervals. Batches of 10 snails were exposed to four different dilutions ofaqueous
extractofbarkofC tigliumand C. variegatum. Dosesareexpressedasfinalconcentration (V/V) of
stembarkinaquarium.Therewasnomortalityincontrolgroup.
Figura 1. Diagramadebarrasquemuestralatoxicidad(LC50)deextractosacuososdecortezadetallos
de Crotón tigliumy Codiaeum variegatumfrente a Lymnaea acuminata (A)y Indoplanorbis
exustus (B)a diferentes intervalosde tiempo. Seexpusierongruposde 10caracolesa 4concentraciones
distintasdeextractosdecortezadeC. tigliumyC.variegatum. Lasdosisseexpresancomoconcentracio-
nesfinales(V/V)decortezaenelacuarion. Nohubomortalidadenelgrupodecontrol
in case of Codiaeum variegatum mortality (96h) in the case of Lymnaea acuminata
it increased from 10% to 90%, when and Indoplanorbis exustus respectively
dosesincreased from0.159mgDW/Lto (TablesI, II).
0.090 mg DW/L (Table III). Same trend Increased in mortality with increa-
was also observed in case of stem bark sed in exposure periods could be affec-
of both the plants at all the exposure ted by several factors, which may be
periods. acting separately or conjointly. For
The positive correlation between example, uptake ofactivemoietyis time
dose and mortality in all cases was dependent, which leads progressive
noted because increase concentration of increase the entrance ofthe drug and its
pesticides inaquariumwaterresulted in effects in the snail body (SiNGH and
more intake or entry ofpesticides in the Agarwal, 1988; 1993a; 1993b). Stability
body ofanimáis. This trend is also inde- (life span) of active moiety of pesticides
pendent upon several factors such as, in environment and the rate of their
rate of penetration, nature of slope, detoxification in animal body also alter
variability and maximal effects of active the mortality and exposure periods,
moieties. relationships (Mitra, Sud and Mitra,
Aqueous preparation of all the plant 1978; Koundinyaand Ramammurthy
parts showed a significant negative 1979; Matsumura, 1985). This possibi-
correlationbetween LC valué and expo- lity cannotbe ruled out in case of plant
sure periods e. g LC50 of látex extracts originpesticidesalso.
of Crotón tiglium were decreased from More important is the fact that the
0.06 mg DW/L (24h); > 0.04 mg DW/L látex of these plants is much more toxic
(48h); > 0.02 mg DW/L (72h); > 0.014 than synthetic pesticides. The present
mg DW/L (96h) and 0.034 mg DW/L study demonstrates that the látex of
(24h); > 0.02 mg DW/L (48h); > 0.015 Crotón tiglium and Codiaeum variegatum
mg DW/L (72h); > to 0.009 mg DW/L have higher molluscicidal activity than
71
Iberus, 19 (1), 2001
any of the prevalent synthetic pyreth- rapid absorption and onset of effects.
roids. Thus, the24hLC50 ofmexacarba- Even though the slope alone is not a
mate (3.5 ppm), aldicarb (30.00 ppm), very reliable indicator of toxicological
farmothion (27.00 ppm), Cypermethrin mechanism, yet it is a useful parameter
(2.5 ppm), permethrin (0.82 ppm) and (Randand Petrocelli, 1988) for such a
fenavalerate (2.5 ppm) against the study. Since the LC50 of the latices of
Lymnaea acuminata (Singh and different euphorbiales lay within the
Agarwal 1981; Singh and Agarwal 95% confidence limits, it is obvious that
1986; 1987; 1988 and 1991; Sahay, Singh in replícate test of random samples, the
ANDAgarwal, 1991) is higher than that concentration response Unes would fall
ofthe Crotón tiglium (0.06ppm)whichis in the same range (Randand Petroce-
about 196 times stronger the standard lli, 1988).
molluscicides niclosamide (LC50 11.8 The doses, that can be, used for
ppm) (SinghandAgarwal, 1984). killing the snails are safe for fish. This is
Statistical analysis of the data on supported by our observations on a
toxicity brings out several important mixedpopulationofsnailsandfish.
points. The x^ test for goodness of fit In conclusión, it is believed that the
(Heterogeneity) demonstrated that the extracts of above plants may be used as
mortality counts were not found to be potent source of molluscicides, because
significantly heterogeneous and other plant products are less expensive, easily
variables, e.g. resistance etc. do not sig- available, easily soluble in water and
nificantly affect the LC50 valúes, as lesshazardoustothenon-targetanimáis
these were found to lie within the 95% thanthesyntheticmolluscicides.
confidence limits. The dose mortality
graphs exhibit steep slope valúes. The
ACKNOWLEDGEMENTS
steepness ofthe slope line indicates that
there is a large increase in the mortality
ofsnailswithrelativelysmallincreasein One ofthe authors (Ram R Yadav) is
the concentration of the toxicant. The thankful to Department ofEnvironment
slope is, thus an index ofthe susceptibi- andForestGovt.ofIndia(SanctionNo.F-
lity ofthe target animal to the pesticides 14/35/96/MAB-RE dated 9.11.1999) for
A
used. steep slope is also indicative of financialassistance.
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