Midgut Genes Knockdown by Oral dsRNA Administration Produces a Lethal Effect on Cotton Boll Weevil

Abstract

The "cotton boll weevil" (Anthonomus grandis Boheman) is a key pest in America whose larval stage develops within the cotton flower bud. During its development, the larva uses the flower bud as food and as a shelter from predators. This behavior limits the effective control through conventional insecticide applications and biocontrol techniques. Increasing genetic information from insects has allowed the development of new control technologies based on the use of RNA interference (RNAi) to design orally delivered double-stranded RNA (dsRNA) strategies. In this study, we evaluated the effect of continuous oral administration of six specific dsRNA in order to identify an effective target gene for RNAi-mediated control of cotton boll weevil. First, six selected A. grandis gene fragments were amplified and cloned to perform in vivo synthesis of the specific dsRNA, and subsequently, larvae and adults were fed with this dsRNA for 2 weeks. Larvae mortality ranged from 40 to 60% depending on the targeted gene sequence. Indeed, α-amylase and cytochrome p450 dsRNAs were the most effective. Oral administration in adults caused smaller but still significant death rates (15-30%). Thus, the results demonstrated RNAi responses depend on life stages and target genes. The dsRNA ingestion was capable of providing knockdown mRNA levels in cotton boll weevil midgut and this effect was significantly higher in the larval stage. In this study, we present a new report of silencing of midgut genes in A. grandis larva induced by continuously feeding with dsRNA. This potential new tool should be further evaluated in cotton boll weevil control strategies.

Characteristics of environmental RNAi in potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Psylloidea: Triozidae)

“…In insects, the developmental stage has been found to influence RNAi penetrance, a phenomenon resulting from differences in the response to exogenous RNAi triggers ( Schmitt-Engel et al, 2015 ). In general, younger insect developmental stages have been found to be more receptive, or sensitive, to knockdown, compared to more advanced life stages (instars) ( Guo et al, 2021 ; Salvador et al, 2021 ; Willow and Veromann, 2021 ). The psyllid life cycle consists of five nymphal instar stages, the newly emerged adult, also referred to as a teneral adult, and the mature adult ( Butler and Trumble, 2012 ).…”

Highly Variable Dietary RNAi Sensitivity Among Coleoptera

“…However, as mortality was only monitored after 26 days (dsRNA treatments were administered for 20 days), there remain critical unknowns with regard to timeliness of RNAi-induced mortality. Salvador et al (2021) reported that 14 days of dietary exposure, using artificial diet overlaid with treatment solutions containing 0.2 μg dsRNA/μl, resulted in 40–60% mortality in cotton boll weevil ( Anthonomus grandis ) larvae, and 10–30% mortality in adults, percent mortality depending on target gene in both life stages.…”

The Transcriptomic Response of the Boll Weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), following Exposure to the Organophosphate Insecticide Malathion

“…Cytochrome P450s are a large group of xenobiotic enzymes that are induced in the cell to handle various stressors including insecticides [ 49 ]. The boll weevil has 59 CYPs in the genome annotated as xenobiotic metabolism and insecticide resistance [ 36 ], of which 23 are found in the gut [ 50 ]. In a previous study, 28 xenobiotic CYPs were shown to be constitutively upregulated in field-collected larvae and adults compared to pupae [ 36 ].…”