A narrow host-range and lack of persistence in two non-target insect species of a bacterial symbiont exploited to deliver insecticidal RNAi in Western Flower Thrips

The thrips gut pH and implications for symbiont-mediated RNAi

The gut pH plays crucial roles in diet preference, habitat choice, insect fitness, and insect-microbial relationships. It significantly impacts enzyme activity efficiency, as well as the internalisation and efficacy of pesticides. Without a comprehensive understanding of the gut environment, potential pest management strategies cannot be fully optimised.This study investigates the gut pH of the globally invasive pest insect Western flower thrips Frankliniella occidentalis, and the effect its Gram-negative symbiotic gut bacterium BFo2 has on pH modulation. Indicator dyes were fed to F. occidentalis and the gut pH was found to vary between 6 and 7. In general, the larval and adult guts appear to have a pH of between 6 and 6.5; however, the posterior gut of some adults appears to be closer to 7. This almost neutral pH offers a favourable environment for the neutrophilic symbiotic BFo2. The ability of BFo2 isolates to buffer pH towards neutral was also observed during in vitro culture using broths at different pH values.This paper also discusses the implications of this gut environment on dsRNAi delivery. By laying the foundation for understanding how gut pH can be leveraged to enhance current pest management strategies, this study particularly benefits research aimed at optimising the delivery of lethal dsRNA through symbiont-mediated RNAi to Western flower thrips in pest management programs.

Potential of Virus-Mediated RNAi of Insect Genes in Plants to Control Aphids

Expression of double-stranded RNAs (dsRNAs) in plants is an emerging strategy to efficiently control insects. RNA interference (RNAi)-mediated pest control takes advantage of double-stranded RNA that can suppress the expression of one or more insect genes that encode key proteins. Virus-induced gene silencing (VIGS) is a useful tool for plant expression of dsRNAs to control pests without altering the plant's genome. Trehalase (TRE) and chitin synthase (CHS) are very important in insects. In this study, we first demonstrated that spraying dsRNAs targeting CHS and TRE increased the mortality rate of the peach aphid Myzus persicae treated with the pathogenic fungus Metarhizium anisopliae. When dsRNAs targeting mpTRE and mpCHS were expressed in plants via VIGS, the expression of mpTRE and mpCHS was reduced in aphids, and their fertility and survival rates were decreased. These results indicate that VIGS-mediated RNA interference is a powerful approach to effectively control aphids, and aphids had a higher mortality rate when M. anisopliae was sprayed.

The multifaceted roles of gut microbiota in insect physiology, metabolism, and environmental adaptation: implications for pest management strategies

Similar to many other organisms, insects like Drosophila melanogaster, Hypothenemus hampei, and Cockroaches harbor diverse bacterial communities in their gastrointestinal systems. These bacteria, along with other microorganisms like fungi and archaea, are essential to the physiology of their insect hosts, forming intricate symbiotic relationships. These gut-associated microorganisms contribute to various vital functions, including digestion, nutrient absorption, immune regulation, and behavioral modulation. Notably, gut microbiota facilitates the breakdown of complex plant materials, synthesizes essential vitamins and amino acids, and detoxifies harmful substances, including pesticides. Furthermore, these microorganisms are integral to modulating host immune responses and enhancing disease resistance. This review examines the multifaceted roles of gut microbiota in insect physiology, with particular emphasis on their contributions to digestion, detoxification, reproduction, and environmental adaptability. The potential applications of gut microbiota in integrated pest management (IPM) are also explored. Understanding the microbial dynamics within insect pest species opens new avenues for pest control, including developing microbial biocontrol agents, microbial modifications to reduce pesticide resistance, and implementing microbiome-based genetic strategies. In particular, manipulating gut microbiota presents a promising approach to pest management, offering a sustainable and eco-friendly alternative to conventional chemical pesticides.

Functions and regulations of insect gut bacteria

The insect gut is a complicated ecosystem that inhabits a large number of symbiotic bacteria. As an important organ of the host insect, the symbiotic bacteria of the insect gut play very important roles in regulating physiological and metabolic processes. Recently, much progress has been made in the study of symbiotic bacteria in insect guts with the development of high-throughput sequencing technology and molecular biology. This review summarizes the primary functions of symbiotic bacteria in insect guts, such as enhancing insecticide resistance, facilitating food digestion, promoting detoxification, and regulating mating behavior and egg hatching. It also addresses some possible pathways of gut bacteria symbiont regulation governed by external habitats, physiological conditions and immunity of the host insect. This review provides solid foundations for further studies on novel theories, new technologies and practical applications of symbiotic bacteria in insect guts. © 2024 Society of Chemical Industry.

A Review on Digestive System of Rhynchophorus ferrugineus as Potential Target to Develop Control Strategies

Rhynchophorus ferrugineus, commonly known as red palm weevil (RPW), is a high-risk insect pest that has become a threat to many important palm species. There are several dominant factors that lead to the successful infestation of RPW, including its stealthy lifestyle, highly chitinized mouthpart, and high fecundity rate. Due to that, millions of dollars of losses have been suffered by many countries invaded by RPW. Several methods have been designed to control its invasion, including the usage of insecticides, but many cause resistance and environmental pollution. Therefore, an environmentally friendly insecticide that targets specific systems or pathways in RPW is urgently needed. One of the potential targets is the digestive system of RPW, as it is the major interface between the insect and its plant host. The related knowledge of RPW's digestive system, such as the anatomy, microflora, transcriptomic analysis, and proteomic analysis, is important to understand its effects on RPW's survival. Several data from different omics regarding the digestive systems of RPW have been published in separate reports. Some of the potential targets have been reported to be inhibited by certain potential insecticides, while other targets have not yet been tested with any inhibitors. Hence, this review may lead to a better understanding on managing infestations of RPW using the system biology approach for its digestive system.