Impact of two insect growth regulators on the enhancement of oxidative stress and antioxidant efficiency of the cotton leaf worm, Spodoptera littoralis (Biosd.)

Nedal Fahmy

doi:10.21608/eajbsa.2012.14956

Abstract

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 4 th 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.

Highlights

Oxidative stress in biological systems is caused by reactive oxygen species (ROS), such as superoxide anion radicals, hydroxyl radicals and hydrogen peroxide, generated during normal oxidative processes in cells and extracellular fluids
Changes in CAT activity in the body tissues of the 4th instar of S. littoralis larvae were monitored for five days post treatment by each of the tested insect growth regulators (IGRs); buprofezin and pyriproxyfen
Regarding to GST activity shown in Table (2), the present study showed that the insecticide buprofezin caused a significant elevation in the enzyme activity which lasted four days post treatment and reached its maximum activity in the 2nd day up to 109% compared to control

Summary

Introduction

Oxidative stress in biological systems is caused by reactive oxygen species (ROS), such as superoxide anion radicals, hydroxyl radicals and hydrogen peroxide, generated during normal oxidative processes in cells and extracellular fluids. ROS levels may increase dramatically, resulting in significant damage to cell structures. This process what is known as oxidative stress (Wang et al, 2001). Oxidative stress is associated with aging and senescence (Arking et al, 2000) Pesticides exert their biological effects via generation of ROS (Sayeed et al, 2003). Oxidative stress has been shown to be associated with exposure to several organophosphorous compounds (Hai et al, 1997) and different classes of pyrethroids (Main, and Mulla, 1992).ROS cause lipid peroxidation; protein, enzyme, and DNA oxidation; and glutathione (GSH) depletion, leading to oxidative damage in insect tissues (Ahmad, 1995). The status of lipid peroxidation and antioxidants in an organism reflects the dynamic balance between the antioxidants defense and pro-oxidant conditions, which serves as a useful index for assessing the risk of oxidative damage (Vijayavel et al, 2006)

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Conclusion