Insights into the Use of Eco-Friendly Synergists in Resistance Management of Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

Rifampicin synergizes the toxicity of insecticides against the green peach aphid, Myzus persicae

Myzus persicae is an important pest that has developed resistance to nearly all currently used insecticidal products. The employment of insecticide synergists is one of the effective strategies that need to be developed for the management of this resistance. Our study showed that treatment with a combination of the antibiotic, rifampicin, with imidacloprid, cyantraniliprole, or clothianidin significantly increased their toxicities against M. persicae, by 2.72, 3.59, and 2.41 folds, respectively. Rifampicin treatment led to a noteworthy reduction in the activities of multifunctional oxidases (by 32.64%) and esterases (by 23.80%), along with a decrease in the expression of the CYP6CY3 gene (by 58.57%) in M. persicae. It also negatively impacted the fitness of the aphids, including weight, life span, number of offspring, and elongation of developmental duration. In addition, bioassays showed that the combination of rifampicin and a detoxification enzyme inhibitor, piperonyl butoxide, or dsRNA of CYP6CY3 further significantly improved the toxicity of imidacloprid against M. persicae, by 6.19- and 7.55-fold, respectively. The present study suggests that development of active ingredients such as rifampicin as candidate synergists, show promise to overcome metabolic resistance to insecticides in aphids.

Key Contributions of the Overexpressed Plutella xylostella Sigma Glutathione S-Transferase 1 Gene (PxGSTs1) in the Resistance Evolution to Multiple Insecticides

The overexpression of insect detoxification enzymes is a typical adaptive evolutionary strategy for insects to cope with insecticide pressure. In this study, we identified a glutathione S-transferase (GST) gene, PxGSTs1, that exhibited pronounced expression in the field-resistant population of Plutella xylostella. By using RNAi (RNA interference), the transgenic fly models, and quantitative real-time polymerase chain reaction (RT-qPCR) methods, we confirmed that the augmented expression of PxGSTs1 mediates the resistance of P. xylostella to various types of insecticides, including chlorantraniliprole, novaluron, λ-cyhalothrin, and abamectin. PxGSTs1 was found to bolster insecticide resistance in two ways: direct detoxification and enhancing antioxidative defenses. In addition, our findings demonstrated that pxy-miR-8528a exerts a pivotal influence on forming insecticide resistance in P. xylostella by downregulating PxGSTs1 expression. In summary, we elucidated the multifaceted molecular and biochemical underpinnings of PxGSTs1-driven insecticide resistance in P. xylostella. Our results provide a new perspective for understanding the insecticide resistance mechanism of P. xylostella.

Effect of novel botanical synergist on the effectiveness and residue behavior of prothioconazole in wheat field

Fusarium head blight (FHB) is a critical fungal disease causes serious grain yield losses and mycotoxin contaminations. Currently, utilization of chemical fungicides is the main control method which has led to serious resistance. Development of novel synergist is an important strategy to reduce the usage of chemical fungicides and postpone the development of resistance, while natural components are interesting resources. In this study, the synergistic effect of Taxodium 'zhongshansha' essential oil (TZEO) was determined and the best synergistic ratio (SR) of 3.96 in laboratory which was observed when the weight ratio of TZEO and prothioconazole was 1 : 1 with the corresponding EC50 (half maximal effective concentration) value of Fusarium graminearum was 0.280 mg L-1. Subsequently, an increase of 6.31% on the control effect to FHB index in field test was observed when compared to the treatment with prothioconazole alone, though there was no significant difference between these treatments. Furthermore, we established an effective method to detect the mycotoxin contaminations in wheat grain with the limits of quantifications (LOQs) value of 5 µg kg-1 (DON, ZEN, 3-DON, and 15-DON) and 1 µg kg-1 (OTA) and the contents were less to the maximum residue limit (MRL) values. It was also shown that the application of 20% TZEO EW led to a 20% reduction in the use of prothioconazole, which was calculated based on the control effect values of 86.41% and 90.20% between the treatments of 30% prothioconazole OD (225 g a.i ha-1, recommend dosage) and 30% prothioconazole OD (180 g a.i ha-1) + 20% TZEO EW (225 mL ha-1), significantly. The initial residue of prothioconazole and prothioconazole-desthio was increased in the treatment with TZEO, which may play an important role in the synergistic effect on FHB. Moreover, none of the treatments posed a prothioconazole residue risk in the wheat grain and the environment. In addition, the essential oil has no any negative influence on wheat growth, which was revealed by a study of the chlorophyll content. These results provide an important botanical synergist for use with prothioconazole to control Fusarium head blight, and in-depth study to the synergistic mechanism of this oil is necessary in our future research.

Leveraging RNA Interference to Impact Insecticide Resistance in the Colorado Potato Beetle, Leptinotarsa decemlineata

The Colorado potato beetle, Leptinotarsa decemlineata Say, is a potato pest that can cause important economic losses to the potato industry worldwide. Diverse strategies have been deployed to target this insect such as biological control, crop rotation, and a variety of insecticides. Regarding the latter, this pest has demonstrated impressive abilities to develop resistance against the compounds used to regulate its spread. Substantial work has been conducted to better characterize the molecular signatures underlying this resistance, with the overarching objective of leveraging this information for the development of novel approaches, including RNAi-based techniques, to limit the damage associated with this insect. This review first describes the various strategies utilized to control L. decemlineata and highlights different examples of reported cases of resistances against insecticides for this insect. The molecular leads identified as potential players modulating insecticide resistance as well as the growing interest towards the use of RNAi aimed at these leads as part of novel means to control the impact of L. decemlineata are described subsequently. Finally, select advantages and limitations of RNAi are addressed to better assess the potential of this technology in the broader context of insecticide resistance for pest management.

Insights into insecticide-resistance mechanisms in invasive species: Challenges and control strategies

Threatening the global community is a wide variety of potential threats, most notably invasive pest species. Invasive pest species are non-native organisms that humans have either accidentally or intentionally spread to new regions. One of the most effective and first lines of control strategies for controlling pests is the application of insecticides. These toxic chemicals are employed to get rid of pests, but they pose great risks to people, animals, and plants. Pesticides are heavily used in managing invasive pests in the current era. Due to the overuse of synthetic chemicals, numerous invasive species have already developed resistance. The resistance development is the main reason for the failure to manage the invasive species. Developing pesticide resistance management techniques necessitates a thorough understanding of the mechanisms through which insects acquire insecticide resistance. Insects use a variety of behavioral, biochemical, physiological, genetic, and metabolic methods to deal with toxic chemicals, which can lead to resistance through continuous overexpression of detoxifying enzymes. An overabundance of enzymes causes metabolic resistance, detoxifying pesticides and rendering them ineffective against pests. A key factor in the development of metabolic resistance is the amplification of certain metabolic enzymes, specifically esterases, Glutathione S-transferase, Cytochromes p450 monooxygenase, and hydrolyses. Additionally, insect guts offer unique habitats for microbial colonization, and gut bacteria may serve their hosts a variety of useful services. Most importantly, the detoxification of insecticides leads to resistance development. The complete knowledge of invasive pest species and their mechanisms of resistance development could be very helpful in coping with the challenges and effectively developing effective strategies for the control of invasive species. Integrated Pest Management is particularly effective at lowering the risk of chemical and environmental contaminants and the resulting health issues, and it may also offer the most effective ways to control insect pests.