Resistance of AustralianHelicoverpa armigerato fenvalerate is due to the chimeric P450 enzyme CYP337B3

Abstract

Worldwide, increasing numbers of insects have evolved resistance to a wide range of pesticides, which hampers their control in the field and, therefore, threatens agriculture. Members of the carboxylesterase and cytochrome P450 monooxygenase superfamilies are prominent candidates to confer metabolic resistance to pyrethroid insecticides. Both carboxylesterases and P450 enzymes have been shown to be involved in pyrethroid resistance in Australian Helicoverpa armigera, the noctuid species possessing by far the most reported resistance cases worldwide. However, specific enzymes responsible for pyrethroid resistance in field populations of this species have not yet been identified. Here, we show that the resistance toward fenvalerate in an Australian strain of H. armigera is due to a unique P450 enzyme, CYP337B3, which arose from unequal crossing-over between two parental P450 genes, resulting in a chimeric enzyme. CYP337B3 is capable of metabolizing fenvalerate into 4′-hydroxyfenvalerate, which exhibits no toxic effect on susceptible larvae; enzymes from the parental P450 genes showed no detectable fenvalerate metabolism. Furthermore, a polymorphic H. armigera strain could be bred into a susceptible line possessing the parental genes CYP337B1 and CYP337B2 and a resistant line possessing only CYP337B3. The exclusive presence of CYP337B3 in resistant insects of this strain confers a 42-fold resistance to fenvalerate. Thus, in addition to previously documented genetic mechanisms of resistance, recombination can also generate selectively advantageous variants, such as this chimeric P450 enzyme with an altered substrate specificity leading to a potent resistance mechanism.pest management | cotton bollworm O ne of the main threats of agriculture nowadays is the rapid development of resistance of pest insect species to control agents worldwide. The cotton bollworm, Helicoverpa armigera (Hübner), is the noctuid species possessing by far the most reported cases of insecticide resistance worldwide with evolved resistance against pyrethroids, organophosphates, carbamates, organochlorines (www.pesticideresistance.org), and recently against the macrocyclic lactone spinosad (1) and Bacillus thuringiensis-derived toxins (2). This capacity is partly due to its distribution, which is one of the widest for any agricultural insect pest species, covering Africa, the Middle East, southern Europe, India, central and southeastern Asia, eastern and northern Australia, New Zealand, and many eastern Pacific Islands (3). In addition, H. armigera is a significant pest of cotton, the single crop most intensively sprayed with insecticides. Almost 30% of all pesticides used worldwide are directed against this insect pest (4). In Australia, the economic losses due to direct yield reduction and pest management of H. armigera and endemic H. punctigera were estimated to be approximately A$150 million in 1990-1991 (5). In addition, H. armigera is highly polyphagous, feeding on 72 known host plant species distributed in 29 families in Australia (6).Af...

The Molecular Genetics of Insecticide Resistance

“…Second, and finally, 2012 has also seen the documentation of a resistance gene arising via gene conversion. In this study, a unique P450 gene CYP337B3 in Helicoverpa armigera, which confers resistance to the pyrethroid fenvalerate, has been shown to have been formed via unequal crossing over between two parental P450 genes (Joussen et al 2012). This novel chimeric P450 can metabolize fenvalerate to the nontoxic 49-hydroxyfenvalerate and therefore has a novel and selectively advantageous substrate specificity.…”

Variation in P450-mediated fenvalerate resistance levels is not correlated with CYP337B3 genotype in Chinese populations of Helicoverpa armigera

“…DNA was extracted from each larva using the AxyPrep Multisource Genomic DNA Miniprep Kit (Axygen Biosciences, CA, USA) as per the manufacturer's instructions. PCR using the three sets of primers (Table S2) described by Joussen et al [14] was then carried out on all samples to distinguish the three possible CYP337 genotypes (B1-B2 and B3 homozygotes and B1-B2/B3 heterozygotes). The PCR conditions involved an initial 94°C denaturation for 5 min, followed by 30 cycles of 94°C for 30 s, 55°C for 30s, and 72°C for 30s, and finally 10 min at 72°C.…”

“…Several individual P450s [12][13][14][15][16][17] and esterases [10,18,19] have been shown to metabolize pyrethroids and some, specifically CYP337B3, CYP6B7, CYP9A12 and CYP9A14 [20][21][22][23], and CCE001a, CCE001c, CCE001d and CCE001i [10,18,19], have also been found to be more highly expressed in resistant strains in at least one study. However quantitative trait loci (QTL) mapping has only so far directly associated one enzyme, CYP337B3, with resistance [14]. This enzyme maps to linkage group (LG) 13, and is encoded by a chimeric P450 gene that has apparently arisen from unequal crossing-over between the closely linked CYP337B1 and CYP337B2 genes.…”

“…In the case of H. armigera, the resistance is generally due to enhanced metabolism, and bioassays with the P450 inhibitor piperonyl butoxide (PBO) and the esterase inhibitor S,S,S-tributyl phosphorotrithioate (DEF) implicate both in the resistance but find that the relative contributions of the two classes of enzyme to resistance vary among populations [6][7][8][9][10][11]. Several individual P450s [12][13][14][15][16][17] and esterases [10,18,19] have been shown to metabolize pyrethroids and some, specifically CYP337B3, CYP6B7, CYP9A12 and CYP9A14 [20][21][22][23], and CCE001a, CCE001c, CCE001d and CCE001i [10,18,19], have also been found to be more highly expressed in resistant strains in at least one study. However quantitative trait loci (QTL) mapping has only so far directly associated one enzyme, CYP337B3, with resistance [14].…”

Acylated Quinic Acids Are the Main Salicortin Metabolites in the Lepidopteran Specialist Herbivore Cerura vinula

“…As the insects' nutritional spectrum is limited to plants of the Salicaceae family (Salix and Populus species), they are regarded as specialist herbivores (Ali and Agrawal 2012;Hintze-Podufal 1970). Numerous metabolic studies (recent examples: Beran et al 2014;Joussen et al 2012;Shelomi et al 2016) have addressed the question whether a specialist herbivore uses a distinct mechanism to cope with the defense of its host plant. In the present publication, we used a double-track strategy: the careful structural identification of metabolic products arising from the diet of the specialist herbivore resulted in an assumption about how the main chemical defense compounds were transformed during digestion.…”