The expression of Spodoptera exigua P450 and UGT genes: tissue specificity and response to insecticides

Cytochrome P450 and UDP-glucosyltransferase (UGT) as phase I and phase II metabolism enzymes, respectively, play vital roles in the breakdown of endobiotics and xenobiotics. Insects can in crease the expression of detoxificatio n enzymes to cope with the stress from xenobiotics including insecticides. However, the molecular mechanisms for insecticide detoxification in Spodoptera exigua remain elusive, and the genes conferring insecticide metabolisms in this species are less well reported. In this study, 68 P450 and 32 UGT genes were identified. Phylogenetic analysis showed gene expansions in CYP3 and CYP4 clans of P450 genes and UGT33 family of this pest. P450 and UGT genes exhibited specific tissue expression patterns. Insecticide treatments in fat body cells of S. exigua revealed that the expression levels of P450 and UGT genes were significantly influenced by challenges of abamectin, lambda-cyhalothrin, chlorantraniliprole, metaflumizone and indoxacarb. Multiple genes for detoxification were affected in expression levels after insecticide exposures. The results demonstrated that lambda-cyhalothrin, chlorantraniliprole, metaflumizone and indoxacarb induced similar responses in the expression of P450 and UGT genes in fat body cells;eight P450 genes and four UGT genes were co-up-regulated significantly, and no or only a few CYP/UGT genes were down-regulated significantly by these four insecticides. However, abamectin triggered a distinct response for P450 and UGT gene expression;more P450 and UGT genes were down-regulated by abamectin than by the other four compounds. In con elusion, P450 and UGT genes from S. exigua were identified, and different responses to abamectin suggest a different mechanism for insecticide detoxification.     

Resistance to neonicotinoid insecticides and expression changes of eighteen cytochrome P450 genes in field populations of Bemisia tabaci from Xinjiang,China

The occurrence of Bemisia tabaci poses an increasingly serious threat to cotton and vegetable crops in Xinjiang, China. Currently, neonicotinoid insecticides are commonly used to control the insect, to which resistance is inevitable due to intensive use. However, the resistance status and mechanism of B. tabaci to neonicotinoid insecticides in Xinjiang are poorly understood. Cytochrome P450 monooxygenases represent a key detoxification mechanism in the neonicotinoid resistance of B. tabaci. In this study, the resistance level to imidacloprid and thiamethoxam was investigated using the leaf dipping method in five field populations of B. tabaci from Turpan (TP, two sampling sites), Shache (SC), Hotan (HT) and Yining (YN) in northern and southern Xinjiang. The expression changes of eighteen cytochrome P450 genes from the select B. tabaci populations were determined by real‐time fluorescence quantitative PCR (qPCR). The bioassay revealed that the five populations tested had developed moderate to high levels of resistance to imidacloprid (12.26–46.07‐fold), while the populations remained sensitive to thiamethoxam except for HT, which had a low level of resistance. The qPCR results showed that the expression levels of five P450 genes, CYP4G68, CYP6CM1, CYP303A1‐like, CYP6DZ7 and CYP6DZ4, were significantly higher in some resistant field populations than in the susceptible strain. Resistance to imidacloprid in field populations of B. tabaci might be associated with the increased expression of these five cytochrome P450 genes. The results are useful for further understanding the mechanism of neonicotinoid resistance and will contribute to the management of insecticide‐resistant B. tabaci in Xinjiang.     

Gene expression profiles of the Southern house mosquito Culex quinquefasciatus during exposure to permethrin

Insecticide resistance is a major obstacle to the management of disease‐vectoring mosquitoes worldwide. The genetic changes and detoxification genes involved in insecticide resistance have been extensively studied in populations of insecticide‐resistant mosquitoes, however few studies have focused on the resistance genes upregulated upon insecticide exposure and the possible regulation pathways involved in insecticide resistance. To characterize the changes in gene expression during insecticide exposure, and to investigate the possible connection of known regulation pathways with insecticide resistance, we conducted RNA‐Seq analysis of a highly permethrin‐resistant strain of Culex quinquefasciatus following permethrin exposure. Gene expression profiles revealed a total of 224 upregulated and 146 downregulated genes when compared to a blank acetone carrier treated control, respectively, suggesting that there were multiple, but specific genes involved in permethrin resistance. Functional enrichment analysis showed that the upregulated genes contained multiple detoxification genes including a glutathione S‐transferase and multiple cytochrome P450 genes, as well as several immune‐related genes, while the downregulated genes consisted primarily of proteases and carbohydrate metabolism and transport. Further analysis showed that permethrin exposure resulted in a decrease in the expression of serum storage proteins and likely represented a delay in the development of the fourth instar possibly due to a decrease in feeding. This effect was more pronounced in an insecticide‐resistant strain than in an insecticide‐susceptible strain and may represent a behavioral mechanism of insecticide resistance in Culex mosquitoes.     

Induction of the mRNA for CYP6B2, a pyrethroid inducible cytochrome p450, in Helicoverpa armigera (Hubner) by dietary monoterpenes

A cDNA clone encoding a cytochrome P450 from H. armigera was used to examine the expression of two homologous cytochrome P450 mRNAs, one of which, CYP6B2, is probably involved in pyrethroid metabolism. The mRNA for CYP6B2 in particular can be induced up to tenfold by peppermint oil and the monoterpene α-pinene as well as to a smaller extent by menthol, butylated hydroxyanisole, and piperonyl butoxide. Both mRNAs are present in the major larval tissues, midgut, fat body, and cuticle, although only the mRNAs in the midgut and fat body are inducible by peppermint oil. The induction is a rapid process occurring within a period of 4 h with a similarly rapid rate of decrease in the absence of the inducing compounds. During normal development both mRNAs are absent from eggs and increase during the larval stage, reaching a maximum during mid fifth instar. Both mRNAs then decrease to undetectable levels during pupation and remain undetectable in the adult stage. © 1997 Wiley-Liss, Inc.     

Molecular mechanisms conferring asymmetrical cross-resistance between tebufenozide and abamectin in Plutella xylostella

Based on the confirmation of asymmetrical cross-resistance between abamectin and tebufenozide in Plutella xylostella, the present work proved that the cytochrome P450 monooxygenase plays a decisive role in cross-resistance, and the expression of various cytochrome P450 (CYP450) genes in different strains was surveyed to elucidate the molecular basis of the underlying mechanisms. Enzyme analysis showed the activity of cytochrome P450 monooxygenase was notable enhanced in the strains resistant to both tebufenozide (3.07-fold) and abamectin (3.37-fold), suggesting that the enhancement of cytochrome P450 monooxygenase is the main detoxification mechanism responsible for the cross-resistance. CYP4M7 (64.58-fold) and CYP6K1 (41.97-fold) had extremely high expression levels in the Teb-R strain, selected using tebufenozide, which was highly resistant to tebufenozide (RR 185.5) and moderately cross-resistant to abamectin (RR 41.0). When this strain was subjected to further selection using abamectin, the resultant Aba-R strain showed a higher expression of CYP6K1 (60.32-fold). However, the expression of CYP4M7 was reduced (10.62-fold). Correspondingly, the Aba-R strain became more resistant to abamectin (RR 593.8) and less resistant to tebufenozide (RR 28.0). Therefore, we concluded that the over expression of CYP4M7 was the main cause for tebufenozide resistance, and that CYP6K1 mainly conferred abamectin resistance. The asymmetrical cross-resistance occurred because tebufenozide selection not only enhanced the expression of CYP4M7, but also that of CYP6K1. This is the first report on the molecular mechanism of asymmetrical cross-resistance between insecticides.     

Cloning and expression of a cytochrome P450 hydroxylase gene from <Emphasis Type="Italic">Amycolatopsis orientalis</Emphasis>: hydroxylation of epothilone B for the production of epothilone F

Degenerate PCR primers were used to amplify cytochrome P450 gene fragments from the high-GC gram-negative bacteria Amycolatopsis orientalis, which catalyzes the hydroxylation of epothilone B to produce epothilone F. The amplified fragments were used as hybridization probes to identify and clone two intact cytochrome P450 genes. The expression of one of the cloned genes in a Streptomyces lividans transformant resulted in the biotransformation of epothilone B to epothilone F. The conversion of epothilone B to epothilone F by the S. lividans transformant was confirmed by mass spectrometry and nuclear magnetic resonance spectroscopy. An erratum to this article can be found at     

Exposure to herbicides reduces larval sensitivity to insecticides in Spodoptera litura (Lepidoptera: Noctuidae)

Herbicides and insecticides are widely used in modern agriculture. It has been reported in various studies that application of insecticides can increase tolerance of herbivorous insects to insecticides. However, limited information exists on susceptibility to insecticides when insects are exposed to herbicides. This study was conducted to investigate the potential impact of the herbicides trifluralin and 2-methyl-4-chlorophenoxyacetic acid sodium salt (MCPA-Na) on the susceptibility of the nocturnal moth Spodoptera litura to the insecticides X-cyhalothrin, phoxim and bifenthrin. We found that larvae exposed to trifluralin or MCPA-Na became significantly less susceptible to both insecticides than nonexposed control larvae. Herbicide-treated larvae did not show altered growth under the used test conditions. However, heads of herbicide-treated larvae showed increased expression of the acetylcholinesterase genes SI Ace I and SI Ace 2. Moreover, the fat body and midgut of herbicide-treated larvae displayed elevated expression of detoxification genes (the carboxylesterase gene SI CarE;the glutathione S-transferase genes SlGSTe2 and SlGSTe3\ the cytochrome P450 monooxygenase genes CYP6B48, CYP9A40 and CYP321B1). The CYP6B48 gene exhibited highest inducibility. In conclusion, the data of this study suggest that exposure of S. litura larvae to herbicides may stimulate detoxification mechanisms that compromise the efficacy of insecticides.     

Oxidative stress,DNA damage,and histological alterations in Bombyx mori exposed orally to pesticide dimethoate

Pesticides are an essential part of agricultural practices that ward off pathogens and diseases from the agricultural crop. However, apart from target organisms, these chemicals also have adverse effects on non-target organisms. Dimethoate is an insecticide used extensively in agriculture and horticulture practices worldwide. We used the silkworm Bombyx mori as a model organism to study the effect of commercial formulation of dimethoate (Dimethoate-30% EC) on the gut, silk gland, and fat body tissues. LD₅₀ of dimethoate-30% EC on silkworm (B. mori) was 997 ppm, as reported in a previous study. We used concentrations of 25, 50, and 100 ppm in our experiments. Our results showed that sub-lethal doses of dimethoate caused weight loss and induced damage at the histological level to the mid-gut, silk gland, and fat body of B. mori. It also caused a decrease in the level of antioxidants like CAT, SOD, GPx, GSH, and GST, indicating that dimethoate has produced a shift of ROS balance towards free radical generation and therefore resulted in overall damage to this organism. Sub-lethal doses of this pesticide also caused lipid peroxidation in the silk gland, gut, and fat body of B. mori, damaging these tissues. The disruption was also seen in the mid-gut and middle silk gland at the DNA level, where it caused single-strand breaks, as was revealed by single cell gel electrophoresis studies. Damage at histological, biochemical, and molecular levels was most extreme at a concentration of 100 ppm, the highest sub-lethal concentration given to B. mori.     

Honey bee (Apis mellifera) gut microbiota promotes host endogenous detoxification capability via regulation of P450 gene expression in the digestive tract

There is growing number of studies demonstrating a close relationship between insect gut microbiota and insecticide resistance. However, the contribution of the honey bee gut microbiota to host detoxification ability has yet to be investigated. In order to address this question, we compared the expression of cytochrome P450s (P450s) genes between gut microbiota deficient (GD) workers and conventional gut community (CV) workers and compared the mortality rates and the pesticide residue levels of GD and CV workers treated with thiacloprid or tau-fluvalinate. Our results showed that gut microbiota promotes the expression of P450 enzymes in the midgut, and the mortality rate and pesticide residue levels of GD workers are significantly higher than those of CV workers. Further comparisons between tetracycline-treated workers and untreated workers demonstrated that antibiotic-induced gut dysbiosis leads to attenuated expression of P450s in the midgut. The co-treatment of antibiotics and pesticides leads to reduced survival rate and a significantly higher amount of pesticide residues in honey bees. Taken together, our results demonstrated that honey bee gut symbiont could contribute to bee health through the modification of the host xenobiotics detoxification pathways and revealed a potential negative impact of antibiotics to honey bee detoxification ability and health.