The present study was conducted for evaluating of the impact of two insect
growth regulators (IGRs) namely, Applaud (buprofezin) as a chitin synthesis inhibitor
and Admiral (pyriproxyfen) as juvenile hormone analogue (JHA) in the larval body of
the cotton leaf worm, Spodoptera littoralis. This evaluation was achieved via (1)
Estimating the antioxidant system response present in the 4th larval instar of S.
littoralis through estimating the activity of two enzymes; catalases (CAT) and
glutathione-S-transferase (GST), as well as an antioxidant compound; glutathione
reduced (GSH). (2) Estimating the accumulated lipid peroxidation in the larval
tissues by evaluating the level of Malonaldehyde (MDA) as an indicator for lipid
peroxidation. Both tested IGRs used in this study showed more or less similar trend in
their mode of action relative to the tested biomarkers in the present work. CAT
showed a significant increase in its activity (42.02%) and (139.26%) for buprofezin
and pyriproxyfen, respectively. This activity lasts for only one day post treatment then
it was inhibited to be very close to that level in normal untreated larvae. This may be
due its consumption in scavenging reactive oxygen species (ROS) produced due to
significant accumulation of MDA. One the other hand, GST showed persisted
increase in its activity especially with buprofezin treated larvae may be to overcome
the deleterious effect of accumulating MDA. Similarly, GSH which serves as a free
radicals scavenger also showed a significant increase in its level especially due to
treatment. The present study which is conducted for the first time, documented the
occurrence of lipid peroxidation due to IGRs treatment in the larval tissues in S.
littoralis larvae which enhanced different antioxidant defensive system to overcome
its effect.