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  

Shima Rahmani , Ali R. Bandani
Plant Protection Department, University College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran
Author    Correspondence author
Molecular Entomology, 2015, Vol. 6, No. 2   doi: 10.5376/me.2015.06.0002
Received: 12 Jan., 2015    Accepted: 28 Feb., 2015    Published: 29 Mar., 2015
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Rahmani and Bandani, 2015, 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, Molecular Entomology, Vol.6, No.2 1-10 (doi: 10.5376/me.2015.06.0002)

Abstract

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 LC50 value in thiamethoxam treatment against A. fabae and H. variegata was 113.85 and 788.55 mg (ai)L-1, respectively and LC50 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.

Keywords
Carboxylesterase; Acetylcholinesterase; Selective insecticides; Hippodamia variegata; Aphis fabae

Aphids are a diverse group of herbivore insect pests causing direct and indirect damage to plant species including sap sucking, transmission of viruses, and secretion of honeydew (Kennedy et al. 1962; Raboudi et al. 2002; Diehl et al., 2013).

Black bean aphid, Aphis fabae Scopoli (Homoptera: Aphididae), is a serious pest in all nymphal stages and adult (Van Emden and Harrington, 2007) that attacks almost 200 host plant species including vegetables, fruit trees and ornamentals causing damage and reducing the market value by sucking the sap from the tender shoots, pods, flowers (Volk and Stechmann 1998; Arocca et al., 2011). It is an important vector of viruses especially on sugar beets, transmitting more than 30 viruses, mainly in the nonpersistent group (Van Emden and Harrington, 2007).
Coccinellid beetles are considered as biological control agents of many injurious insects like aphids with a great economic importance in agro-ecosystem (Agarwala and Dixon 1992; Diehl et al., 2013). They are of a great value as aphids predators both in their larval and adult stages (Hippa et al. 1978; Kring et al. 1985; Gardiner et al., 2012). Hippodamia variegata (Goeze) originated in the Palearctic region (Gordon 1987). It is a widespread predator of aphids in many parts of the world (Franzmann 2002; Kontodimas and Stathas, 2005) and many agricultural ecosystems such as wheat, tobacco, cotton, vegetable and orchards (Yang et al. 1997; Wu et al., 2010; Honek et al., 2014).
This species is considered as the most important natural enemies of aphids, coccids and other soft bodied insects such as psyllids, white flies, lepidop­teran insects, and mealy bug (Franzman 2002). In IPM programs the integration of chemical and biologicalcontrols is a common practice and indeed the exact concept of IPM is developed as a result of applying compatible pesticides with biological control (Elzen, 2001). Application of pesticides in IPM programs could lead to both lethal and sublethal effects on arthropods, thus in addition to death, they can adversely affect life parameters (Rahmani and Bandani, 2013).
Among pesticides, pirimicarb (a carbamate chemical) is a selective insecticide used mostly for aphid control (Dewar et al., 2014; Hughes et al., 2014) which acts as acetylcholinterase inhibitor. Moreover, in recent years, neonicotinoid-class insecticides, as agonists on nicotinic acetylcholine receptors that mimic the mode of action of nicotine in postsynaptic nerve membranes, are used for the control of aphids (Chao et al., 1997; Nauen et al., 1998). Thiamethoxam, a neonicotinoid insecticide, presently is an effective chemical for the control of sucking pests such as aphids, whiteflies, thrips, some microlepidoptera, and a number of coleopteran species (Sharma and Lal, 2002).
Exposure to pesticides may result in both behavioral and physiological changes in individuals especially when individual exposed to sublethal concentrations. The physiological changes caused by sublethal concentrations of insecticides can reduce developmental rate, longevity, fecundity, and fertility (Stark and Banks, 2003; Rahmani and Bandani, 2013). However, in IPM (Integrated Pest Management) program, application of selective pesticides in order to maintain beneficial species populations is mandatory. There are reports of the differential insecticide susceptibility of prey and predator (Wu and Miyata, 2005; Booth et al., 2007; Karunaratne et al. 2007; Lima et al., 2013), which is as a result of physiological and biochemical differences between the prey and its predator to detoxify insecticides. Yu (1987, 1988) examined selectivity relationships between predator and prey by comparing detoxification enzyme systems and reported that the predator showed more detoxifying enzyme activity than its prey. Biochemical changes after sublethal exposure to pesticides can be measured using specific biomarkers (like general esterases and acetylcholinesterase) that provide a measure of effects, e.g., “fitness” of the survivors (McCarthy and Shugart 1990; Kumral et al., 2011).
Among different enzymes involved in detoxification process, acetycholinesterases (AChE, EC 3.1.1.7.) and general esterases (CarEs, EC 3.1.1.1) play essential role in these processes (Baffi et al 2005). General esterases are a large and diverse group of hydrolases that hydrolyze numerous substrates including esters and certain non-ester compounds (Walker and Mackness, 1983). They are commonly classified into three types based on their interactions with OP compounds (Aldridge, 1993). The A-esterases are not inhibited by OPs but degrade these insecticides as their substrates, whereas the B-esterases are readily inhibited by OPs (Aldridge, 1953). The third type, the C-esterases, that was later added to the classification, do not interact with OPs (Bergmann et al., 1957). The insect esterases can either cause broad spectrum resistance to various insecticides through rapid binding and slow turnover of insecticide molecules (sequestration) or cause narrow spect
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