Abstract
The Colorado potato beetle, Leptinotarsa decemlineata (Say), is a significant agricultural pest that has developed resistance to many insecticides that are used to control it. Investigating the mechanisms of insecticide detoxification in this pest is important for ensuring its continued control, since they may be contributors to such resistance. Multidrug resistance (MDR) genes that code for the ABCB transmembrane efflux transporters are one potential source of insecticide detoxification activity that have not been thoroughly examined in L. decemlineata. In this study, we annotated the ABCB genes found in the L. decemlineata genome and then characterized the expression profiles across midgut, nerve, and Malpighian tubule tissues of the three full transporters identified. To investigate if these genes are involved in defense against the macrocyclic lactone insecticide ivermectin in this insect, each gene was silenced using RNA interference or MDR protein activity was inhibited using a chemical inhibitor, verapamil, before challenging the insects with a dose of ivermectin. Survival of the insects did not significantly change due to gene silencing or protein inhibition, suggesting that MDR transporters do not significantly contribute to defense against ivermectin in L. decemlineata.
Highlights
The Colorado potato beetle, Leptinotarsa decemlineata (Say), is a major pest of solanaceous crops with a large geographical distribution that includes much of North America, and areas of Europe, and Asia, with potential to spread elsewhere [1,2]
multidrug resistance (MDR) genes belong to the B subfamily of ATP-binding cassette (ABC) transporters and seven members of this family were found to be present in L. decemlineata (Table 2), compared to six identified in the model coleopteran, Tribolium castaneum [45]
Comparing the two beetle species, three efflux transporter genes of the full two-module type were found in L. decemlineata compared to two that are present in T. castaneum
Summary
The Colorado potato beetle, Leptinotarsa decemlineata (Say), is a major pest of solanaceous crops with a large geographical distribution that includes much of North America, and areas of Europe, and Asia, with potential to spread elsewhere [1,2]. Control of L. decemlineata often includes the use of chemical insecticides; due to extensive exposure to insecticides, this species has developed resistance to 55 different products in 13 different chemical groups [3]. One of many mechanisms by which insects respond to xenobiotic insult, including insecticide exposure, is through metabolic detoxification and subsequent excretion [4]. Enzymes such as esterases, glutathione-S-transferases (GSTs), UDP-glycosyltransferases (UGTs), and cytochrome P450-dependent monooxygenases (CYPs) metabolize harmful molecules to reduce their toxicity or make them more transported (phase I and II reactions), while transmembrane efflux transporters, such as multidrug resistance (MDR) proteins, facilitate their elimination or sequestration (phase III reactions). MDRs are Insects 2020, 11, 135; doi:10.3390/insects11020135 www.mdpi.com/journal/insects
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