Abstract:
The integration of biological and chemical control
approaches is very important for a
successful Integrated Pest Management (IPM) program
. Demographic approaches give a
better understanding of the side effects of pestici
des on beneficial organisms. In this study,
laboratory bioassays were set up to evaluate the le
thal and sublethal effects of diazinon
and fipronil on different stages of
Trichogramma brassicae
Bezdenko (Hymenoptera:
Trichogrammatidae). The effects of Field Recommende
d Concentration (FRC) of
diazinon and fipronil were studied on larvae, prepu
pa and pupae of the parasitoid.
Diazinon and fipronil reduced adult emergence by 99
.74 and 50.46%, respectively. The
LC
50
values for diazinon and fipronil on adult stage we
re 0.11 and 0.46 μg ai ml
-1
,
respectively. The sublethal effects of the chemical
s were studied on life-table parameters
of the parasitoid emerging from parasitized eggs ex
posed to the FRC of the insecticides at
larval stage and also adults exposed to
LC
30
of the insecticides. Longevity and progeny
production were affected by the insecticides in com
parison to the control. Three main life-
table parameters including intrinsic rate of increa
se (
r
m
), Doubling Time (DT) and net
Reproduction rate (
R
0
) were negatively affected by the sublethal treatme
nts. The intrinsic
rate of increase for control, diazinon and fipronil
exposed populations at larval stage were
0.28, 0.23 and 0.12, respectively and were 0.26, 0.
04 and 0.08 for populations exposed to
LC
30
at adult stage, respectively. The sex ratio of off
spring at all insecticide treatments has
led to the production of female offspring by the ch
emicals. These findings showed that
diazinon and fipronil were harmful for
T. brassicae
, thus semifield and field studies are
suggested for getting more applicable results for p
ossibly using them in IPM programs.
Keywords:
Biological control, Life-table parameters, Parasito
id,
Trichogramma
brassicae
