Metabolic resistance to organophosphate insecticides in natural populations of the whitefly Bemisia tabaci (Hemiptera: A
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ORIGINAL ARTICLE
Metabolic resistance to organophosphate insecticides in natural populations of the whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) in Egypt and molecular identification of mitotypes El-Sayed H. Shaurub & Jorge R. Paredes-Montero & Judith K. Brown & Haggag S. Zein & Amr A. Mohamed Received: 18 April 2020 / Accepted: 12 October 2020 # Springer Nature B.V. 2020
Abstract The whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) cryptic species has become an important pest of cotton and vegetable crops in Egypt. In this study, resistance to three organophosphate insecticides (OPs), chlorpyrifos-methyl, profenofos and pirimiphosmethyl, and detoxification enzymatic activities of acetylcholinesterase, carboxylesterase, and monooxygenase were evaluated to establish baseline resistance levels for B. tabaci infesting cotton in seven Egyptian governorates, compared to a susceptible laboratory reference B. tabaci colony. Resistance to OPs ranged from low-to-moderate or low-to-high, while detoxification enzymatic activities were predominantly governorate-dependent. Phylogenetic Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12600-020-00858-9) contains supplementary material, which is available to authorized users. E. 10). Chlorpyrifos-methyl was found to be associated with the highest RR for B. tabaci individuals (Table 3), and so these surviving females were subjected to the respective biochemical assays. Detoxifying enzyme activity Sample preparation Whitefly survivors (Prabhaker et al. 2014) were homogenized in distilled water (50 mg, fresh body weight mL−1) using a Teflon-glass tube homogenizer (GlasCol 099C K5424CE system, Glas-Col LLC, Terre Haute, IN, USA) cooled in a polystyrene jacket containing crushed ice. Homogenates were centrifuged at
Phytoparasitica
Fig. 1 Distribution map of different locations from which Bemisia tabaci samples were collected in Egypt. Numbers denote the order of locations listed in Table 1, and letters correspond to locations listed in Table 2
10,000 g for 45 min at −4 °C, except for the MFO activity bioassay for which microsomal pellets were prepared using an established protocol (Hansen and Hodgson 1971), with centrifugation at 105,000 g, at −4 °C for 30 min. The supernatant was stored at −20 °C until enzyme activity and protein content were determined. Three replicated experiments were conducted for each bioassay. Total protein content was determined using the Bradford Assay (Bradford 1976).
AChE activity The AChE [EC 3.1.1.7] activity was measured, using a previously described approach (Simpson
et al. 1964), using acetylcholine bromide (AChBr) as a substrate. The reaction mixture containing 200 μL of enzyme solution, 0.5 mL of 0.067 M phosphate buffer (pH 7) and 0.5 mL of 3 mM AChBr, was incubated at 37 °C for 30 min. One mL of alkaline hydroxylamine (equal vol of 2 M hydroxylamine hydrochloride and 3.5 M of NaOH) and 0.5 mL HCl (conc. HCl-distilled water, 1:2 v/v) were added. The mixture was shaken and held at
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