Correlation between toxic natures of pyrethroid and behavioral response of desert locusts.

Abstract

Optomotor normal visual response of the locust Schistocerca gregaria was compared when injected (between 1st and 2nd thoracic segments) with 10, 5, 2.5 and 1.25 microg/g body weight doses of Permethrin after different intervals of time (just after injection, 10 and 20 minutes). LD50 value for Permethrin was calculated to be 3.0 microg/g. Results are analyzed statistically by t. test and ANOVA technique. It was noticed that there was a significant decrease of vision (P<0.005, Table II) in treated locusts and at the same time Permethrine effect is significantly time related (P<0.05, ANOVA, table III). Correlation between increasing age, weight and increasing toxicity has also been established. The inhibition of neural enzyme Cholinesterase with Permethrin and as a result more accumulation of acetylcholine at nerve junctions and less passage of the transmission of impulses thus less response from the locusts has also been explored and discussed.

Full text

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Pakistan Journal of Pharmaceutical Sciences
Vol13(2), July 2000, pp.13-19
CORRELATION BETWEEN TOXIC NATURE OF PYRETHROID
AND BEHAVIORAL RESPONSE OF DESERT LOCUSTS


F. RAFI, RUQAIYA HASSAN, HABIB FATIMA AND FARHAT ZAFAR
Department of Physiology, University of Karachi


ABSTRACT:
Optomotor normal visual response of the locust Schistocerca gregaria was compared
when injected (between 1st and 2nd thoracic segments) with 10, 5, 2.5 and 1.25 µg/g body
weight doses of Permethrin after different intervals of time (just after injection, 10 and 20
minutes). LD50 value for Permethrin was calculated to be 3.0 µg/g. Results are analyzed
statistically by I. test and ANOVA technique. It was noticed that there was a significant
decrease of vision (P<0.005, Table II) in treated locusts and at the same time Permethrine
effect is significantly time related (P<0.05, ANOVA, table III).
Correlation between increasing age, weight and increasing toxicity has also been
established. The inhibition of neural enzyme Cholinesterase with Permethrin and as a
result more accumulation of acetylcholine at nerve junctions and less passage of the
transmission of impulses thus less response from the locusts has also been explored and
discussed.

INTRODUCTION

In laboratory the degree of toxicity of an insecticide was based mainly on the manner in
which the insecticide made contact with the insect. The insecticide was usually applied as a
formulation and composition of formulation could effect the rate of penetration of an insecticide
into the body of the insect. A decreased toxicity could be due to less penetration of the insecticide
rather than a real decrease in the toxicity of the insecticide (MacCuaig, 1957; Parry, 1964, and
Ahmed and Gardiner, 1979).

Toxicity of insecticide was effected by the mode of application. Injection of the insecticide in
the body was more toxic than its topical application (Farnham et al., 1965). The main reason for
these toxicity variations was perhaps the presence of efficient mechanism of detoxification in
insects due to which a rapid build up at the site of toxic action was prevented or delayed either due
to less penetration or lack of active transportation to site of toxic action (Ahmed and Gardinar,
1968). Difference in susceptibility to insecticides in different regions of the body had also been
reported by Ahmed and Gardiner (1968, 1969). They observed that malathion had more toxic
effect when applied to neck membrane of desert locust than to other parts of the body.

Much of the above mentioned work had been done to show that how the mode of contact, the
site and detoxification mechanism of insect effect the toxicity of the different insecticides. No
observation had been reported showing effect of insecticides on eyes of locusts specifically
relating to their resolving power.

An effort was made to estimate the variations in the behavioral responses from the locusts by
use of different concentrations and doses of Pyrethroids which are an important set of insecticides.

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14
Correlation between Toxic Nature
MATERIAL AND METHODS

Adults of both sexes of Schistocerca greearfa were obtained from the desert area of Sind,
Pakistan and were reared in our laboratory. Experimental set up including recoding, stimulating
and illuminating device of Burn and Rail (1974) and Horridge (1966) were used in this work. For
calculating and injecting different doses of insecticides, dosage calculator and microdrop
apparatus capable of giving small measured volumes of insecticidal solutions (MacCuaig and
Watts, 1960) were used.

Insecticide Permethrin belonging to Pyrethroids group of insecticides was used in this work.
Solutions of 10, 5, 2.5 and 1.25 µg/g. body weight of Permethrin were prepared in xylene (because
Permethrine is only miscible in this solvent) at room temperature. Each insect was weighed and
the amount of insecticide (actual ingredient) adjusted according to the body weight. The volume of
the insecticide applied to each locusts therefore varied according to the dose as well as to the
weight of the insect.

Various sites of application of insecticide in locusts were tried. Injection of insecticide
between 1st and 2nd thoracic segment was proved to be best to give more toxic effects on the vision.
The record of resolving power from the locust both treated and control were recorded by
Physiograph, whose pen was calibrated such that it moved through 0.5mm, on the recording paper,
when 0.1 volts of current was passed through it. So by simply measuring the height of the spike on
the recording paper, resolving power of the locust was determined in volts.

Table I
Effect of Various Doses of Permethrin on Visual Responses of Locusts
Schistocerca gregoria, Average of 10 Locusts in each case
Difference is Mean ± S.E.
Visual responses of locusts at different intervals before and after
treatment with insecticides (volts)



S. No.


Dose
µ µg/g
B.W.
Before
Treatment
Just after
Treatment
10 Mins.
After
Treatment
20 Mins.
After
Treatment
----
30 Mins.
After
Treatment
----
40 Mins.
After
Treatment
---- 7.36
± 0.023
0.7
±0.307
*


1) 10









7.39
± 0.010
7.17
± 0.472
4.08
± 0.048
3.17
± 0.47
2) 05
*





7.38
± 1.013
7.03
± 0.03
5.12
± 0.044
3.51
± 0.132
5.58
± 0.312

7.4**
± 0.00
7.375**
± 0.014
3) 2.5




7.45
± 0.266
7.49
± 0.073
5.86
± 0.073
6.79
± 0.179
4) 1.25
----
* = Dead, **= Become Normal

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F. Rafi et al.
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Table II

Dose µ µg/g B.W.
Normal with just
After treatment
Normal with 10
mins. after treatment
Normal with 20
mins. after treatment
5 7.17 ± 0.472 4.08 ± 0.048* 3.17 ± 0.47*
2.5 7.03 ± 0.03* 5.12 ± 0.044* 3.51 ± 0.012*
1.25 7.49 ± 0.073 5.86 ± 0.073* 6.79 ± 1.179***

** = P<0.005
*** = P<0.025
Difference is Mean ± S.E.

Table III
Comparison of Effect of Different Doses of Permethrin at Different Time Intervals
on Visual Responses of Locust Schistocerca gregaris

ANOVA
Source
DF SS MS F
A 3 21.33 7.11 7.561
B 2 4.86 2.43 2.59
Error 6 5.63 0.94
Total 11 31.82

* = P<0.05
A = Times (Just after Treatment) 10 & 20 Mins. After Treatment
B = Doses (5, 2.5 & 1.25 pg/g of 6. W. Permethrin)


RESULTS AND DISCUSSION

Average values of resolving power of ten adult locusts with different doses of Permethrin
were studies with different intervals of time (Table-I). A value of 3.0 µg/g. body weight was
estimated as LD50 value for permethrin. All P. values are calculated by t-test and ANOVA
technique.


With high dose, 10 µg/g. of Permethrin the response of the locust decreased sharply from
normal value of 7.36 ± 0.02 to 0.7V ± 0.30 volts in one to two minutes after injection compared to
6.79 t 0.17 volts after 20 minutes of injection with a dilute dose of 1.25 pg/g. body weight (Fig.
IA and ID). Similar decreasing responses from normal were also observed with toxicities ranging
between two above-mentioned doses (Fig. 1-b 5 µg/g. and 1-c 2.5 µ/g). The pattern of response
was different for different doses i.e. with lower toxicities normal response was regained in matter

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16
Correlation between Toxic Nature
of 10-20 minutes which was never obtained or delayed with higher toxicities (Fig. 1).

Effect of different doses of Permethrin on visual response was then calculated statistically by
t-test and ANOVA technique. It had been noticed (Table II) that there was a significant decrease
in the vision of locusts (P<0.005) and insecticidal effect is significantly time related (P<0.05,
ANOVA, Table III).

Toxicity of an insecticide depends on factors like mode and site of application of insecticide
and also on weight and sex of an insect.

Studies showed that toxicity of insecticide is effected mainly by mode and site of its
application is extensively undertaken by many workers (Ahmed and Gardiner, 1968, 1970;
MacCuaig, 1958) and the present studies also confirm the previous findings. MacCuaig (1958)
working on locusts had reported that when malathion was applied topically to the vertex, it killed
locusts more quickly and in greater number than when applied to the abdomen. These findings
were also confirmed by Ahmed and Gardiner (1968, 1970).

Our data also supports the above observations that toxicity of an insecticide depended mainly
on mode and loci of its application. We have explored experimentally that injection of insecticide
between first and second thoracic segment proved to be the best mode and site for getting
excellent toxicity results.

Latter Ahmed and Gardiner (1970) confirmed their previous findings by emphasizing that
there were some inherent differences in the susceptibility of various body regions associated
perhaps with the differential vulnerability of some vital internal organs as central nervous system.

Permethrin like all synthetic pyrethroids kills insects by strongly exciting their nervous
system, rather than sending a single impulse, Permethrin exposed nerves send a train of impulses.
This excitation is because Permethrin blocks the movements of sodium ions from outside to inside
of nerve cells (Vijverhery, 1990).

It had been examined extensively that toxicity of insecticides varied with age and particularly
weight of an insect. The change in toxicity between age groups might be due to differences in the
rate of penetration through the cuticle. More penetration in instars is due to thin cuticle as
compared to the adult locusts. Age of the locusts combined with different weights could cause
great changes in the toxicity of an insecticide (MacCuaig, 1957; Farnham, et al., 1965; and Haque
and Jaleel, 1969).

Research work done also reveals the fact that sensitivity of Pemethrin is also related age to
adults being less affected than children (Cantalamena, 1993 and Caroline Con 1998).

Our work also confirmed the above findings showing that locusts having less weight were
greatly effected by the insecticides which was perhaps due to the fact that the cuticle is sot) and
more permeable to insecticide in less weight locusts. But penetration of insecticide was tine only
when the insecticide was applied topically. In our work insecticide was injected in the body
through first and second thoracic segment but same degree of differences in toxicity were
observed between light and heavy locusts may be due to their tolerance ability.

MacCuaig and Sawyer (1951) had noticed the differences in toxicity, males being easily
effected by insecticide than females. Latter MacCuaig et al. (1958) had confirmed these results

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F. Rafi et al.
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showing that females required more than twice as much insecticide per locust to obtain the same
percentage kill of both sexes.

Some differences in sex and toxicity was also noticed in our experiment. Females always
responded more strongly to given stimulus than males of same age but with less weight. Similarly
males showed more toxic effects to insecticide than females of approximately same age but more
weight.

It is well known fact that insecticides particularly Organophosphates act as potent inhibitors
of neural enzyme cholinesterase in insects (Winteringahm, 1955; Mengle and Casida, 1960.
MacCuaig, 1962 b; Parry, 1964; Bigley, 1966; Burt, et al., 1966; O’Brinc, 1966, 1969 and Eugene,
et al., 1966). Due to inhibition of Cholinesterase, acetylcholine accumulated at the nerve junctions
and hindered the transmission of the impulses, the more toxic the insecticide more inhibition of
the Cholinesterase. Thus more accumulation of acetylcholine and less response from the locusts.
Permetherin inhibits a variety of nervous system enzymes, ATPase, monoamine oxidase-A and
thus there is an increased release of acetylecholine with reduced breakdown (Al-Rahiji 1990, Rao
& Rao 1993 & 1995).

Our studies also yielded the same results as obtained above i.e. higher doses (10, 5 µg/g, body
wt.) of Permethrin inhibited more cholinesterase, as a result accumulated more acetylcholine
accumulated at nerve endings and thus showed less responses as compared to dilute doses of
Permethrin (2.5, 1,25 µg/g body wt.).

So we can conclude our findings that visual response of locusts is effected by Permethrin
(Pyrethorids) and with lower concentration the visual response after initial degradation became
normal again, this reversible change in response may be due to existence of an efficient
mechanism of detoxification which was also reported by Ahmed (1969) in locusts. This aspect
needs some molecular biochemical and histological studies before making final recommendation
on large scale use of Permethrin.