Distribution, Purification and Biochemical Characterization of an Esterase from Red Palm Weevil Rhynchophorus ferrugineus (Olivier) (Coleoptera: Curculionidae) Larvae

Abstract

Red palm weevil (RPW) Rhynchophorus ferrugineus is the most destructive insect pest of numerous palm species in the world and the larval stage (grubs) is the most destructive stage. Great variation in general esterase (GE) activity is recorded among the major tissues and the fat body of the 12th instar larvae has the highest enzyme activity. A major GE isoenzyme is purified to homogeneity to a specific activity 1871.2 U/mg protein. R. ferruginous GE was biochemically characterized to estimate the compounds required for suppressing the enzyme. The enzyme has optimum activity at pH 8.0 and at a temperature of 50°C, irreversibly denatured above 60°C, is induced by Hg2+, Ni2+, Zn2+, Cu2+, Co2+, completely suppressed by Fe2+, appearing to be a Zn2+-dependent enzyme. The enzyme hydrolyzed various phosphoric esters as substrates, has high specificity towards PNPA and α-NA with Km values 0.4 and 0.8 mM. R. ferruginous GE is completely inhibited by PMSF, β-ME, DTT, and 49% by EDTA. The enzyme was inhibited competitively by PMSF and noncompetitively by β-ME and DTT with Ki values 1.5, 2.0 and 3.5 mM. The inhibition of GE can increase the susceptibility of the target pest to chemical insecticides and is appropriate for enhancing the insecticidal efficacy of the chemical insecticides. Further studies in vivo are in progress to investigate the deleterious effect of EDTA, Fe2+, and thiol reducing agent on RPW larval development and the possibility of introducing them as insecticide synergists in IPM programs for developing RPW management strategies.