الفهرس 
INTRODUCTION
Characterization of termite.Only 14 pages are availabe for public view
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Abstract
In the current study, toxicological, biochemical investigations were carried out to analyze and understand the mechanism (s) of pyrethroid resistance in the sand termite, Pasmmotermes hypostoma. Toxicological experiments were conducted to study the susceptibility of three different populations of the test insect to deltamethrin, α-cypermethrin and ƛ-cyhalothrin.
The esterase profiles of the two resistant populations (Dar El-salaam populations and Qena populations) were compared with that of the susceptible populations (Elkawther) using Native PAGE electrophoresis techniques. Further, the in vitro ability of the tested pyrethroids to inhibit esterase activity was studied. Finally, the activity of cytochrome P450 linked monooxygenase of the workers was compared in the different populations.
6.1 Insecticide bioassay
• The workers of both Dar El-salaam population and Qena population have displayed high degree of resistance against the three pyrethroids used in comparison to the susceptible population (Elkawther). Dar El-salaam population was more resistant than Qena population to all the pyrethroids tested.
• The pattern of pyrethroid resistance in this study is characterized by high LC50 values combined with low slopes for ld-p (Log-dose vs probit mortality) lines that suggest a wide variation in the susceptibility of individuals of the same populations.
• Among the three pyrethroids tested, Dar El-salaam population and Qena population displayed higher resistance ratio against α-cypermethrin followed by ƛ-cyhalothrin, while deltamethrin was found to be highly effective compound and poorly resisted by both the resistant populations.
6.2 The role of esterase
• Dar El-salaam population and Qena population have 2.39 and 2.51-fold higher esterase activity, respectively, than that of the susceptible population using α-naphthyl acetate.
• The kinetic parameters, Km and Vmax indicate that Dar El-salaam population and Qena populations have a higher active esterase than that of the susceptible population characterized by high substrate binding affinity as the Km values of both Dar El-salaam(0.180 µmol) and Qena populations (0.177 µmol) were lower than that of the susceptible population (0.235 µmol). This also is supported by higher Vmax values for Dar El-salaam population (0.610) and Qena population (0.633) compared to the susceptible populations (0.322).
• Using β-naphthyl acetate as substrate revealed that Dar El-salaam and Qena populations have 3.46 and 2.46-fold higher esterase activity, respectively, than that of the susceptible population.
• The esterase of the resistant populations have higher substrate binding affinity compared to the susceptible population as the Km values of both Dar El-salaam (0.212 µmol) and Qena populations (0.216 µmol) were lower than that of El-kawther susceptible (0.298 µmol). The maximum velocity of the esterase of the resistant populations where higher than that of the susceptile population as the Vmax values were 0.620, 0.583 and 0.213 for Dar El-salaam, Qena, and El-kawther populations, respectively.
• Correlation analysis showed positive correlation between esterase activity and pyrethroid resistance with correlation coefficient (r) of 0.359, 0.340 and 0.740 for deltamethrin, α-cypermethrin and ƛ-cyhalothrin, respectively when α-naphthyl acetate was used as a substrate and strong positive correlation between esterase activity and pyrethroid resistance was noticed with correlation coefficient (r) of 0.819, 0.803 and 0.998 for deltamethrin, α-cypermethrin and ƛ-cyhalothrin, respectively when esterase activity measured using β-naphthyl acetate as a substrate.
• Five esterase isozymes were identified and designated as E1- E5, from the slowest migrating esterase (highest molecular weight) E1, to the fastest (lowest molecular weight), E5. While four esterase bands were common to both susceptible and resistant populations, susceptible populations lacked one esterase isozume, E4 that was found in the resistant populations.
6.3 Inhibition studies
In order to confirm the role of esterase in the detoxification of the selected pyrethroids, the binding of the selected pyrethroids to esterase enzymes was studied by measuring the inhibition potency of pyrethroid to esterase activity
• The tested pyrethroids were found to be more potent (lower IC50 values) against esterase of the resistant populations (Dar El-salaam and Qena) compared with the esterase of the susceptible population El-kawther).
• α-cypermethrin (To which high resistance factor was developed) was more potent as esterase inhibitor with lower IC50 value (14.031 µg/ml) against the esterase of the highly resistant population (Dar El-salaam) compared to deltamethrin (IC50= 24.898 µg/ml) and ƛ-cyhalothrin (IC50= 14.161 µg/ml)
6.4 The role of cytochrome P450 linked monooxygenase
In the current study, the activity of cytochrome P450 linked monooxygenase was estimated in the workers of the three populations selected. The total cytochrome P450 content was determined using the carbon monoxide differences spectra, following reaction with sodium dithionite.
• The resistant populations, i.e., Dar El-salaam population and Qena population, were found to have 2.99 and 1.74 fold higher monooxygenase activity compared to the susceptible population.
• Correlation analysis revealed strongly positive correlation between monooxygenase activity and pyrethroid resistance with correlation coefficient (r) of 0.96, 0.96 and 0.95 for deltamethrin, α-cypermethrin and ƛ-cyhalothrin, respectively.
Overview
The present study provided toxicological and biochemical, evidence on pyrethroid resistance and its mechanisms in the Egyptian populations of the sand termites, P. hypostoma. The results of this study revealed that P. hypostoma has developed high resistance level against pyrethroid insecticides. This study supports the structure-activity view that the cross-resistance between pyrethroids depends on their chemical structure. The kind of improvement of insecticidal activity by that the substitution of chlorine by broomine in case of deltamethrin enhanced the insecticidal activity and reduced the resistance level in the resistant populations compared to α-cypermethrin which is similar in its structure to deltamethrin. This provides evidence that it is possible and more practical to find resistance-breaking pyrethroids such as deltamethin which are active against resistant populations than increase the doses of pyrethroids that are highly resisted by field populations of P. hypostoma.
The data obtained in the current study revealed the important role of detoxification enzymes in pyrethroid resistance in P. hypostoma. Two detoxification enzymes viz., esterase and monooxygenase were found to be responsible for pyrethroid resistance. Strong positive correlation between esterase activity and pyrethroid resistance was reported. The pyrethroid-resistant populations of P. hypostoma were found to have elevated esterase activity and also additional esterase isozyme which were not observed in the susceptible populations. The biochemical studies provided important evidence that the elevated cytochrome P450 monooxygenase activity observed in the pyrethroid-resistant populations is associated with resistance in the Egyptian populations of P. hypostoma.
As a sequel to this study, it would be worthwhile to determine the relative role of monooxygenase and esterase activity in the workers of P. hypostoma in relation to pyrethroid resistance.