332 T. Venkatesan and S. K. Jalali
(1 spray), Helicide (Ha NPV—2 sprays), Pad-
son (1 spray), cypermethrin and chlorpyriphos
(4 sprays), acephate and imidochloprid (1 spray)
were sprayed during the season, in susceptible
strain released plots Fame, Sumo powder, Con-
fidor and acephate were sprayed twice, in farm-
ers’ practice plot insecticides sprayed were Dom,
Ankur, Bancip, Lancer gold, cypermethrin, chlor-
pyriphos, acephate, endosulfan and imidacloprid
twice in a week.
Trichogramma chilonis (new insecticides tol-
erant strain and susceptible strain) was released
in treatments T 1 and T 2 @ 50,000/ha/release in
the form of parasitized eggs to cover the egg lay-
ing period of P. xylostella. The release of para-
sitoids commenced with moth capture in phero-
mone traps in all the area. Eight days old parasit-
ized cards were released at weekly interval from
July to August, 2007.
The eggs parasitism was recorded at each
treatment in 10 subplots. Twenty plants in each
subplot at each location were observed for the
egg masses, number of larvae and number of
feeding punctures. Thus, 200 plants were ob-
served each time per treatment. The yield data
were recorded at the end of trial. Data on egg
parasitism, no. of larvae/plant and feeding punc-
tures, and yield data were subjected to one-way
ANOVA and means were separated by CD values
at 5 %, wherever ANOVA was significant.
Results and Discussion
Initial LC 50 Values for Field and
Laboratory Collected T. chilonis
The results are presented in Table 1. The LC 50
values obtained for three insecticides, viz., endo-
sulfan, monocrotophos, and fenvalerate after 6 h
of constant exposure is indicated in Table 1. LC 50
values of laboratory population was 0.08, 0.003,
and 0.01 compared to 1.07, 0.70, and 0.04 for the
field-collected population after 6 h of constant
exposure to endosulfan, monocrotophos, and fen-
valerate, respectively (Table 1 ). The significant
χ^2 value for all the three tests indicated heteroge-
neity in the test.
Initial Temperature Response for Field
and Laboratory Populations of T.
chilonis
The results on initial evaluation of laboratory
and field-collected populations exhibited differ-
ential response to higher temperature during 6
and 24 h exposure period. At 32 and 36 °C, and at
variable temperature of 32–38 °C, indicated very
low mortality in both populations. However at 40
and 45 °C, significantly high mortality was re-
corded in the laboratory population compared to
the field-collected population. At 32 °C, no mor-
tality was recorded upto 6 h exposure, indicat-
ing that this temperature is not higher threshold
temperature for survival of T. chilonis. However
at 40 °C, mortality of the adults was 59.7 % in
laboratory population compared to 0.0 % in the
field-collected population and it differed sig-
nificantly amongst the populations (LSD = 5.92,
P = 0.05). The laboratory population was found
to be highly prone to next higher temperature of
45 °C as 96.1 % adults died within 6 h as com-
pared to 9.2 % in the field-collected population.
The low mortality recorded in the field-collected
population suggests that adaptation to higher
temperature is necessary to enhance potential of
T. chilonis in high temperature (Table 2 ).
The results of exposure to high temperature
for 24 h exhibited different results than 6 h ex-
posure. The mortality in laboratory population
(SS) was 47.7, 96.9, 100.0, 100.0, and 98.5 % as
compared to 45.6, 77.7, 90.7, 97.1, and 57.1 % in
32, 36, 40, 45 °C and 32–38 °C, respectively. The
different response of field-collected and labora-
tory populations to high temperature originates
from its physiological adaptation to extreme
temperature. The heat hardening is a well-known
form of acclimatization in many invertebrates
where exposure to high but sub-lethal tempera-
ture protects against subsequent heat induced
death and heat hardening enhanced adult fitness
in the field under hot conditions. The selection
of Trichogramma lines for improvement of para-
sitization at constant low, medium, or high tem-
perature indicated that a change in performance
at one temperature concurrently resulted in oppo-
site changes at distant temperature. Thus, genetic