Development, Characterization and Field Assessment of Multiple Insecticides ... 335
is, 3.0 ml/L increased mortality to 100.0 % and
after constant selection for 10 generations mor-
tality declined to 80.0 % and after 71 generations
of selection, it further declined to 75.0 %. The
results indicated that exposing parasitoids con-
tinuously to insecticides enhances its surviving
ability. In fenvalerate treatment, initial mortality
was 94.0 % and after 36 generations of selection
it declined to 75.0 % and it remained consistent
till 45th generation. The increase in concentra-
tion, i.e., 0.4 ml/lit increased mortality to 95.0 %
and after constant selection for 10 generations
mortality declined to 60.0 % and after 71 genera-
tions of selection, it further declined to 57.0 %.
The results indicated that exposing parasitoids
continuously to insecticides enhances its surviv-
ing ability. The result of parasitizing ability of T.
chilonis when adults were exposed to sprayed
situation is presented in Fig. 1. The initial egg
parasitism obtained was 45.0, 35.0 and 50.0 %
when exposed to endosulfan, monocrotophos
and fenvalerate treatments at high temperature.
The percent egg parasitism ranged from 45.0 to
60.0 % up to 12 generations after 24 h of con-
stant exposure and increased to 75.0–90.0 % and
remained high till 50th generation. Increase in
concentration resulted in decrease in parasitism.
The parasitism ranged from 55.0–70.0 % for an-
other 10 generations and from 66th generation on-
wards, egg parasitism increased to 80.0–95.0 %
and remained ≥ 90.0 % throughout the selection
period. The results thus indicated usefulness of
adapting multiple insecticide tolerant strain to
high temperature to obtain a combined popula-
tion, which is tolerant to all three insecticides and
also to variable high temperature.
LC 50 Values to Determine Increased
Tolerance to Insecticides and
Temperature
The initial LC 50 values of T. chilonis existing
population at the start of the work to three in-
secticides viz., endosulfan, monocrotophos, and
fenvalerate were 1.07, 0.70 and 0.04 ml/l, respec-
tively. However, after exposure for 81 genera-
tions to three insecticides, LC 50 values increased
by 5.16, 6.27, and 6.0 times as compared to im-
mediately after collecting parasitoids from the
field. The formula applied to know percent in-
crease in tolerance levels (T-C x 100/T) revealed
that tolerance level to endosulfan, monocroto-
phos and fenvalerate increased by 98.2, 94.98
and 25.0 % over laboratory population. Therefore
continuous exposure to insecticides starting from
low selected dosages induced tolerance in popu-
lation (Table 4 ).
In India cotton alone consumes maximum
pesticide usage (44.5 %) followed by paddy-
22.8 % and fruits and vegetables-7 % of the total
pesticide consumption (Dudani and Sengupta
1991 ). Trichogramma sp. is used as a bioagent
on lepidopterous pests attacking cotton, cere-
als, vegetables and fruits. The amenability of the
parasitoid for mass rearing and release has con-
tributed to its greater utility. However, greater
reliance on synthetic pesticides had altered the
ecological niche of the bioagent and reduced its
potential. The development of resistance to in-
secticides has been more aggressive in insect pest
of commercial crops like cotton, vegetables and
fruits, where the onslaught of insect pests and
also the consumption of pesticides is more. For
the suppression of borers in the above mentioned
crops, trichogrammatids have been widely used
as biological control agent and of which particu-
larly H. armigera P. xylostella L. have developed
resistance to major group of pesticides. Many of
the pesticides are extremely toxic to bioagents
and this has warranted the development of tol-
erant strain of parasitoid. The trichogrammatids
are susceptible to a broad spectrum of insecti-
cides and reduced parasitism has been reported
in T exiguum and T. pretiosum against H. zea and
Manduca sp. in plots treated with pyrethroids
(Campbell et al. 1991 ) (Table 3 ).
Similarly, the drift of pesticide even a mile
away and single application of pesticides in
cotton reduced the efficacy of trichogramma-
tids (Stinner et al. 1974 ; Bull and House 1983 ;
Bull and Coleman 1985 ; Jalali and Singh 1993 ).
Artificial selection in the laboratory improved
resistance in Aphytis melinus generating a car-
baryl-tolerant line with LC 50 5.13-time as great
as the corresponding base colony and 19.7-time