Field Evolved Resistance in Helicoverpa armigera (Lepidoptera: Noctuidae) to Bacillus thuringiensis Toxin Cry1Ac in Pakistan

Abstract

Helicoverpa armigera (Hübner) is one of the most destructive pests of several field and vegetable crops, with indiscriminate use of insecticides contributing to multiple instances of resistance. In the present study we assessed whether H. armigera had developed resistance to Bt cotton and compared the results with several conventional insecticides. Furthermore, the genetics of resistance was also investigated to determine the inheritance to Cry1Ac resistance. To investigate the development of resistance to Bt cotton, and selected foliar insecticides, H. armigera populations were sampled in 2010 and 2011 in several cotton production regions in Pakistan. The resistance ratios (RR) for Cry1Ac, chlorpyrifos, profenofos, cypermethrin, spinosad, indoxacarb, abamectin and deltamethrin were 580-fold, 320-, 1110-, 1950-, 200-, 380, 690, and 40-fold, respectively, compared with the laboratory susceptible (Lab-PK) population. Selection of the field collected population with Cry1Ac in 2010 for five generations increased RR to 5440-fold. The selection also increased RR for deltamethrin, chlorpyrifos, profenofos, cypermethrin, spinosad, indoxacarb, abamectin to 125-folds, 650-, 2840-, 9830-, 370-, 3090-, 1330-fold. The estimated LC50s for reciprocal crosses were 105 µg/ml (Cry1Ac-SEL female × Lab-PK male) and 81 g µg/ml (Lab-PK female × Cry1Ac-SEL male) suggesting that the resistance to Cry1Ac was autosomal; the degree of dominance (DLC) was 0.60 and 0.57 respectively. Mixing of enzyme inhibitors significantly decreased resistance to Cry1Ac suggesting that the resistance to Cry1Ac and other insecticides tested in the present study was primarily metabolic. Resistance to Cry1Ac was probably due to a single but unstable factor suggesting that crop rotation with non-Bt cotton or other crops could reduce the selection pressure for H. armigera and improve the sustainability of Bt cotton.

Effect of Bt Soybean on Larvae of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

“…The larvae of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) are known for their high population outbreaks, difficulty of control, and enormous damage to crops worldwide (Alvi et al, 2012;Degrande & Omoto, 2013;Feng et al, 2010). The larvae are polyphagous and damage many commercially important crop plants including cotton, legumes in general, sorghum, corn, and tomato, among others (Liu et al, 2010;Chelliah et al, 2011).…”

“…Traditionally, the species has been managed mainly through chemical control; however, it rapidly develops resistance to pesticides (Bués et al, 2005;Alvi et al, 2012). Bt soybean, which expresses the Cry1Ac protein from Bacillus thuringiensis Berliner, is a potential alternative control measure for H. armigera populations, since it can be used in managing the species (Yu et al, 2013).…”

Characterization of Helicoverpa Zea Single Nucleopolyhedrovirus Isolated in Brazil During the First Old World Bollworm (Noctuidae: Helicoverpa Armigera) Nationwide Outbreak

“…The larvae are naturally more tolerant to most of the common insecticides requiring higher application rates to be controlled efficiently (McCaffery, 1998). Almost 30% of all pesticides used worldwide are directed against H. armigera (Ahmad, 2007) although the management of outbreaks has so far been ineffective and also has induced the appearance of resistant insect phenotypes (Oakeshott et al 2013;Rowley et al 2011) including engineered plants expressing Bacillus thuringiensis (Bt) toxins (Alvi et al 2012). Therefore, other naturally found disease-causing pathogens like baculoviruses are important alternatives for the integrated and effective control of Helicoverpa (Rowley et al 2011).…”

Toxicity and Cross-Resistance of Insecticides to Cry2Ab-Resistant and Cry2Ab-Susceptible <I>Helicoverpa armigera</I> and <I>Helicoverpa punctigera</I> (Lepidoptera: Noctuidae)

“…High exposure to Bt toxins expressed in transgenic cotton combined with higher than expected resistance frequencies to Cry toxins in Australian populations of Helicoverpa spp. (Mahon et al 2007b, Downes et al 2009) may increase resistance risk for other insecticides (Alvi et al 2012).…”