SOME STUDIES ON THE TOXICITY OF CONVENTIONAL AND ...

Galleria mellonella were collected in a new vial and the
females of B. hebetor were given healthy larvae of G.
mellonella for further parasitization.
B. Rearing of greater wax moth Galleria mellonella:
Adults were kept in plastic jars (diameter, 5cm and depth
30cm) along with cotton soaked with 20-30% honey
solution to feed. Folded paper sheets were put in jars for
egg laying. The paper sheets with eggs were transferred
to the artificial diet (crushed wheat, bees wax, dates juice,
yeast, and glycerin). The jars were placed in a growth
chamber at 30 ±1°C and 65 ± 5 % r.h. until adult
emergence.
C. Bioassay:
For bioassay study, the residual vials method was used.
The commercial formulations of chlorpyrifos, profenofos,
lufenuron, emamectin benzoate and methoxyfenozide
were obtained from the local market. The concentrations
of different insecticides were prepared on the basis of
their recommended doses against Spodoptera litura and
ten percent above and below the recommended doses. A
sample containing 2 ml of each insecticides concentration
was put in the vials with the help of dropper. The vials
were rolled with hands, then air dried because acetone
dries rapidly in the air. 30 (one day old) adults of Bracon
hebetor that were freshly emerged were introduced in
vials with the help of aspirator. Each concentration was
replicated four times. The vials were covered with muslin
cloth to prevent escape of parasitoids. The vials were
placed in growth chamber running at temperature 30
±1°C and 65 ± 5 %R.H. The mortality of adult parasitoids
was noted at 12, 24, 36 and 48 hours intervals. The data,
thus noted, were analyzed statistically at 5% level of
probability using Duncan’s Multiple Range Test.
RESULTS
The mortality of newly emerged adults of Bracon
hebetor, observed 12, 24, 36 and 48 hours after treatment
with different insecticides at different dose rates is
presented in Table 1.
All insecticides gave significant mortality of Adult
parasitoids as compared to the untreated check (Acetone).
Chlorpyrifos and profenofos were found to be the most
toxic for the parasitoid at their different doses after 36
hours of exposure. Complete mortality of the adult
parasitoid was observed in Chlorpyrifos with all doses
after 36 hrs of exposure. Emamectin benzoate was found
to be the least toxic for all of its doses used in this
experiment even after 48 hours of exposure of the
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Pak. Entomol. Vol. 27, No.1, 2005
parasitoid. A total of 28.25 adult parasitoids was killed
after 48 hours of exposure with 110ml per acre dose rate.
However, with the recommended dose of emamectin
benzoate (100ml/Acre) 21.75 insects were killed.
Methoxyfenozide and lufenuron were found to be
moderately toxic with their recommended doses (100ml
and 50 ml per acre, respectively) after 24 and 36 hours of
exposure. However, their higher doses (110ml and 55ml,
respectively) gave complete mortality after 48 hours.
DISCUSSION
The results of the present study showed that chlorpyrifos
was highly toxic for B. hebetor at all of its doses. Same
results were obtained by Baker and his co-fallows in
1995. They compared the field strains of B. hebetor with
laboratory strains for their resistance against various
organophosphates and other insecticides. They found that
laboratory strains were more susceptible to the
insecticides belonging to organophosphate group.
Different doses of profenofos were also found to be toxic
for B. hebetor after 36 hours of exposure. These results
were also in confirmation with the results of Baker et al.
1995 and Mandal et al. 1995. Amongst new chemistry
insecticides, emamectin benzoate was found to be least
toxic at almost all of its doses. There was no published
work on this insecticide for its toxicity against B.
hebeotor. The insecticides lufenuron and methoxy
fenozide were found to be moderately toxic.
No closely compatible data so far published similar to the
present work was available, thus, based on present results
obtained it can be concluded that none of the insecticides
can be considered completely safe for B. hebetor as far as
application on cotton is involved. Nevertheless, release of
parasitoids would be considered appropriate after 48
hours of application of insecticides on crop in case of
organophates and other persistent insecticides. The new
chemistry insecticides like emamectin benzoate,
lufenuron and mehtoxyfenozide, being less toxic are
hence recommended for integration. The parasitoid
should be released at least after 24 hours of the
application of these insecticides.
ACKNOWLEDGEMENTS
The present work is a part of Ph.D research of the first
author. Sincere thanks and gratitude are expressed to
Dr. Sohail Ahmed, Associate Professor, Department of
Agri. Entomology, for his kind supervision and valuable
suggestions for this research.