Esterase profile changes in ladybeetle, Hippodamia variegata Goeze (Coleoptera: Coccinellidae) and its prey, Aphis fabae Scop. (Homoptera: Aphididae) affected by two insecticides, thiamethoxam and pirimicarb

Black bean aphid, Aphis fabae Scopoli (Homoptera: Aphididae), is a cosmopolitan and serious pest of diverse plant species. In addition to inflicting direct damage, it is an important vector of viruses producing indirect damages. Hippodamia variegata , is considered as aphids predator both in their larval and adult stages. Thus, the aim of the current study was to investigate toxicological, biochemical and physiological effects of two widespread used pesticides against aphids including pirimicarb and thiamethoxam on third instar larvae of the ladybeetle and the adult female of the aphid in laboratory condition. Bioassay showed that LC 50 value in thiamethoxam treatment against A. fabae and H. variegata was 113.85 and 788.55 mg (ai)L -1 , respectively and LC 50 value for pirimicarb treatment against two insects was 2.94 and 2740.07 mg (ai)L -1 , respectively. Enzyme assays showed that AChE and CbE (evaluated by a -NA) of A. fabae inhibited significantly by pirimicarbtreatments(P>0.05), whilst thiamethoxam treatment did not affect both enzymes. Both insecticides did not affect H. variegata AChE and CbE activities, significantly. Polyacrylamide gel electrophoresisof general esterases of A. fabae by a solution mixture of both substrates ( a - and b -NA) showed that only one band present in the control and in the treated insects. However, in H. variegata larvae, there were four esterase isoforms in the control and the isoforms showed changes after insect treatment with the insecticides. Thus it is concluded that susceptibility of the two insects toward the two insecticides are different and these differences were obvious in their enzyme activity and their isoforms as well.