International Journal of Horticulture 2015, Vol. 5, No.16, 1
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emergence (%) or reduction in parasitism (%) over
controls were evaluated by toxicity categories of
International Organization for Biological Control
(IOBC)/West Palaearctic Regional Section (WPRS)
(Hassan et al., 1994; Sterk et al., 1999): 1= harmless
(E < 30%); 2 = slight harmful (30 ≤ E ≤ 79%); 3 =
moderately harmful (79 < E ≤ 99%); 4 = harmful ( >
99 %), where ―E‖ stand for effect of the pesticide on
the biological control agent measured as the reduction
in percentage of emergence or parasitism over control.
3 Results
Analysis of variance for dose demonstrated significance
difference regarding emergence and parasitism (Table
1 and 2). Emergence from the immature stages
demonstrated increase in rate of emergence through
decrease in concentration of fipronil (Table 1). All
used doses in the larval treatment were significantly
different (p≤ 0.05) from their control treatments, while
in the pupal treatment, both 0.04x and 0.02x doses
showed statistically at par (p> 0.05) with respective
control treatments.
In the Table 1 and Figure1, fipronil demonstrated reduced
toxicity for emergence of parasitoids when dose shifted
from higher concentration toward lower concentration.
fipronil in the current study revealed as harmful at
0.4x as well as 0.2x doses, moderately harmful at both
0.08x and 0.04x doses, while slightly harmful for
emergence of
T. chilonis
when larval stage of
parasitoids was treated at 0.02x dose. However, when
pupae of parasitoids were treated, 0.4x dose showed as
moderately harmful, both 0.2x and 0.08x doses were
slightly harmful, while, the remaining two doses
demonstrated as harmless for the emergence of
T. chilonis.
The results in Table 2 showed increase in mean parasitism
rate of the previously treated eggs of
S. Cerealella
when dose shifted from 0.2x toward 0.02x, and also
indicated that all the used doses were slightly harmful
for parasitism except 0.02x dose, which was harmless
for parasitism. Similarly, percentage parasitism
relative to control (Figure 2) revealed that 0.02x dose
showed good mean parasitism of 87.7% relative to
control, while the remaining doses showed mean
parasitism approximately ≤ 70% relative to control.
4 Discussion
In this present study, fipronil was proved as one of the
most harmful chemical for emergence of as well as
parasitism of the previously treated host eggs by
T.
chilonis
in the agro-ecosystem. This chemical showed
severe lethal as well as parasitism effects on
T.
chilonis
even at lower doses of half field dose (< 0.5x)
including 0.4x and 0.2x doses. For successful
integration with
Trichogramma
or any other natural
enemies in particular agro-ecosystem requires more
studies under field condition. Furthermore, it should
be noted that the repeated use of this lower dose might
be responsible for the development of resistance in
pest species.
Figure 1 Percentage reduction in emergence over control of
T.
chilonis
from the host eggs of
S. cerealella
treated with fipronil
at larval and pupal stages of parasitoid
Figure 2 Percentage parasitism relative to control of host eggs
of
S. cerealella
by
T. chilonis
previously treated with fipronil
Sufficient literature is not available on fipronil toxicity
to
Trichogramma
or any other parasitoids. However,
previous literature showed few studies to assess the
adverse impacts of the chemical at field dose on
survival of adults
Trichogramma
and their parasitism
of host eggs. Khan et al. (2015b) found that fipronil
was slightly harmful at field dose for parasitism of the
