Esterases And Antioxidant Enzymes Of The Cotton Pests Helicovepa Armigera And Diparopsis Castanea
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Date
2013-03-14
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Abstract
Helicoverpa armigera and Diparopsis castanea are pests of economic importance in a number of crops, such as cotton, in Zimbabwe. The excessive use of insecticides such as organophosphates
and pyrethroids, in the control of H. armigera has subjected it to high selection pressure. Many detoxifying enzymes of insects are thought to be responsible for insecticide resistance. The
enzymes include the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), OTdiaphorase (OTO) as well as the glutathione S-transferases (GST) and esterases (EST). This study was aimed at measuring these enzyme activities in H. armigera collected from two geographical sites in Zimbabwe. The effect of diet (natural vs artificial) and age (instar) on the activities was also determined. A comparison was also made between the enzyme activities in H. armigera and O. castanea in samples collected from the same geographical area. Whole insects were homogenised in buffer and the homogenate was centrifuged at 15,000 x g and the supernatant was used to measure enzyme activity. Esterase activity was measured using three different substrates to differentiate aryl (phenyl acetate) and carboxylesterase (alphanaphthyl acetate and 4-nitrophenyl acetate) activity.
Neither H. armigera diet nor geographical location produced any significant change in SOD,
CAT, OTO or GST activities. Diet and geographical location did, however, produce a difference
in the esterase activities depending on the substrate used. Age did not affect SOD, CAT, OTD and GST activities. Esterase activity varied with age and the 3rd and 5th instars showed generally lower activity than the 4th instar. When 3rd and 4th instars of red bollworm Oiparopsis castanea and H. annigera were compared,the SOD, CAT and OTO activities again showed little differences while the GST activity washigher in H. arnligera than O. castanea. The esterase activity using all three substrates was also found to be higher in H. annigera. Thus, in general, antioxidant enzyme activity did not vary significantly while esterase activity varied with diet and age and was species dependent.Our data suggests that there is likely to be an age and species dependent susceptibility to organophosphate pesticides for H.annigera and D.castanea.
Description
Presented at the 10th International Congress on the Chemistry of Crop Protection in 2002.
Keywords
Esterase, Enzymes, Cotton, Pests