Rapid evolution of insecticide resistance in the Colorado potato beetle, Leptinotarsa decemlineata

Optimizing dsRNA sequences for RNAi in pest control and research with the dsRIP web platform

BACKGROUND

RNA interference (RNAi) is a tool for studying gene function and has emerged as a promising eco-friendly alternative to chemical pesticides. RNAi relies on delivering double-stranded RNA (dsRNA), which is processed into small interfering RNA (siRNA) to silence genes. However, so far, knowledge and tools for optimizing the dsRNA sequences for maximum efficacy are based on human data, which might not be optimal for insect pest control.

RESULTS

Here, we systematically tested different siRNA sequences in the red flour beetle Tribolium castaneum to identify sequence features that correlated with high efficacy using pest control as a study case. Thermodynamic asymmetry, the absence of secondary structures, and adenine at the 10th position in antisense siRNA were most predictive of insecticidal efficacy. Interestingly, we also found that, in contrast to results from human data, high, rather than low, GC content from the 9th to 14th nucleotides of antisense was associated with high efficacy. Consideration of these features for the design of insecticidal dsRNAs targeting essential genes in three insect species improved the efficacy of the treatment. The improvement was associated with a higher ratio of the antisense, rather than sense, siRNA strand bound to the RNA-induced silencing complex. Finally, we developed a web platform named dsRIP, which offers tools for optimizing dsRNA sequences, identifying effective target genes in pests, and minimizing risk to non-target species.

CONCLUSIONS

The identified sequence features and the dsRIP web platform allow optimizing dsRNA sequences for application of RNAi for pest control and research.

Investigating insecticide resistance in eggplant fruit and shoot borer: Multi-class insecticides and detoxification gene expression

Eggplant fruit and shoot borer, Leucinodes orbonalis (Lepidoptera: Crambidae), is a destructive borer pest that infests eggplant crop from nursery stage to fruiting. This study aimed to evaluate the current insecticide resistance status of L. orbonalis collected from ten different locations of Tamil Nadu, India, using a fruit dip bioassay. Late second instar larvae were exposed to spinosad, spinetoram, thiacloprid and emamectin benzoate. Median lethal concentration (LC50) and resistance ratios (RR) were estimated for each population using a susceptible NBAIR population as a reference. The results showed that emamectin benzoate was highly toxic to L. orbonalis. All field populations exhibited a low to high level of resistance against spinosad (7.4 to 72.1 fold) and spinetoram (6.6 to 67.8 fold), while susceptibility to low levels of resistance was observed against thiacloprid (0.89 to 5.06 fold) and emamectin benzoate (1.48 to 11.29 fold). Additionally, detoxification enzyme assays were conducted for cytochrome P450 monooxygenases (CYP/MFO), glutathione S-transferases (GST) and carboxylesterases (CarE) revealing high specific activity in the Dharmapuri (DMP) population, correlating with resistance. Furthermore, quantitative real-time PCR analysis was conducted to assess detoxification gene expression in resistant (DMP) and susceptible populations after insecticide exposure, revealing significant overexpression of cyp306a1 and ce125 across the studied insecticides, particularly after 48 h, indicating their key role in resistance. These findings highlight the need for insecticide rotation with different modes of action to mitigate resistance development in L. orbonalis, providing valuable insights for sustainable pest management in Tamil Nadu and similar agricultural contexts worldwide.

Exposure Risk Identification and Priority Control List Development of Pesticides in Agricultural Cultivation Areas

The adverse effects of 33 typical pesticides in dry and paddy lands in typical cultivation areas of China were investigated. First, the resistance and cross-resistance (for target organisms), toxicity, and joint toxicity (for nontarget organisms) of pesticides were evaluated, and nine pesticides with high resistance, three with wide cross-resistance, nine with high toxicity, and one with wide joint toxicity were screened. Second, the optimal synergist control schemes in dry and paddy lands were developed, under which resistance to target organisms (corn aphid, soybean aphid, and rice water weevil) reduced by 23.46%, 46.06%, and 26.36% (maximum), respectively, and toxicity (neurotoxicity and developmental toxicity) to nontarget organisms (ladybird beetle, parasitic wasp, and Chinese mitten crab) reduced by 38.83%, 17.76%, and 15.94% (maximum), respectively. Third, the multitoxicity (neurotoxicity, metabolic toxicity, developmental toxicity, carcinogenicity, reproductive toxicity, and respiratory toxicity) adverse outcome pathway based on human health risk was constructed, and 10 pesticides with higher risk and composite risk were identified. Finally, the total exposure risk of 33 typical pesticides was predicted, and a priority control list was proposed. This study provides theoretical guidance for controlling pesticide application to achieve the green and sustainable development of agricultural soils.

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.

Gene expression atlas of the Colorado potato beetle (Leptinotarsa decemlineata)

The Colorado potato beetle (CPB) is a major pest of potato crops, known for its remarkable ability to develop resistance to more than 50 pesticides. For decades, CPB has served as a model species for studying insecticide resistance, insect physiology, diapause, reproduction, and evolution. However, research progress on CPB has been hindered by the lack of comprehensive genomic and transcriptomic resources. Here, leveraging a recently established chromosome-level genome assembly, we constructed a gene expression atlas of CPB using transcriptomic data from 61 samples representing major organs and developmental stages. By integrating short- and long-read sequencing technologies, we enhanced the genome annotation and identified 6,623 additional genes that were previously undetected. Furthermore, we developed a web portal to facilitate the search and visualization of the gene expression atlas, providing an accessible resource for the research community. The CPB gene expression atlas offers valuable tools and comprehensive data that will accelerate future research in pest control and insect biology.

Silencing ACE1 Gene with dsRNA of Different Lengths Impairs Larval Development in Leptinotarsa decemlineata

In the search for effective strategies to control the Colorado Potato Beetle, RNA interference technology has emerged as a promising method due to its capacity to suppress genes selectively. Factors such as the target gene and double-stranded RNA (dsRNA) length are critical for optimizing gene silencing efficiency. In this study, we designed and synthesized in vitro dsRNAs of varying lengths targeting the ACE1 gene, which encodes the AChE1 isoform of acetylcholinesterase in the beetle. All tested dsRNA lengths (222 bp, 543 bp, 670 bp, and 870 bp) promoted transcript reduction. The 670 bp dsRNA was the most effective, reducing transcript levels by approximately 40% by day seven, followed by the 543 bp dsRNA. No significant differences were observed between the 222 bp and 870 bp dsRNAs. Furthermore, all of the dsRNA lengths resulted in reduced weight gain and increased mortality in larvae, with the 670 bp dsRNA showing the highest mortality rate, leaving only 63% larval survival, a trend that persisted through day nine. These findings emphasize that dsRNA length is a key factor in the silencing response, underscoring the importance of selecting the optimal length while considering the gene's target, stability, and delivery methods. This study contributes to establishing design criteria for dsRNA, aiding in the development of more effective and sustainable pest management strategies.

The quest for the best target genes for RNAi-mediated pest control

RNA interference (RNAi) has emerged as an eco-friendly alternative to classic pesticides for pest control. This review highlights the importance of identifying the best target genes for RNAi-mediated pest control. We argue that the knowledge-based approach to predicting effective targets is limited by our current gaps of knowledge, making unbiased screening a superior method for discovering the best target processes and genes. We emphasize the recent evidence that suggests targeting conserved basic cellular processes, such as protein degradation and translation, is more effective than targeting the classic pesticide target processes. We support these claims by comparing the efficacy of previously reported RNAi target genes and classic insecticide targets with data from our genome-wide RNAi screen in the red flour beetle, Tribolium castaneum. Finally, we provide practical advice for identifying excellent target genes in other pests, where large-scale RNAi screenings are typically challenging.

Isolation and identification of entomopathogenic fungi strains for Colorado potato beetle (Leptinotarsa decemlineata) control

AIMS

The Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae) is the most widespread insect pest that causes major economic losses, especially on potatoes. Due to heavy insecticide use, this species now resists most pesticides, posing a significant control challenge. Frequent pesticide application also harms non-target organisms, the environment, and human health. Hence, utilizing biocontrol agents like entomopathogenic fungi (EPF) offers a viable alternative for pest management. The aim of this study was to identify and characterize new EPF strains isolated from soil samples and evaluate their efficacy against adult L. decemlineata under laboratory conditions.

METHODS AND RESULTS

Soil samples were collected in potato fields or uncultivated areas adjacent to the field in the Czech Republic and the EPF strains were isolated using a modified Tenebrio bait method. A total of 20 fungal strains were isolated and identified using morphological and molecular markers based on the 28S rRNA, ITS, and elongation factor 1-alpha gene sequences as Beauveria bassiana (Bals.-Criv.) Vuill., Beauveria brongniartii (Sacc.) Petch, and Cordyceps fumosorosea (Wize) Kepler, B. Shrestha & Spatafora (Hypocreales: Cordycipitaceae), Purpureocillium lilacinum (Thom.) Luangsa-ard, Houbraken, Hywel-Jones & Samson (Hypocreales: Ophiocordycipitaceae), Metarhizium brunneum (Petch), and Metarhizium robertsii Bisch., Rehner & Humber (Hypocreales: Clavicipitaceae). The bioassays revealed high variability among virulence of these strains against L. decemlineata with the shortest median time to death (LT50 = 5 days) in M. robertsii strain MAN3b.

CONCLUSIONS

Results shown that some EPF strains, particularly those of genera Metarhizium, can be promising biocontrol agents against the Colorado potato beetle.

Six-year monitoring of pesticide resistance in the Colorado potato beetle (Leptinotarsa decemlineata Say) during a neonicotinoid restriction period

The Colorado potato beetle (CPB; Leptinotarsa decemlineata) is an important potato pest with known resistance to pyrethroids and organophosphates in Czechia. Decreased efficacy of neonicotinoids has been observed in last decade. After the restriction of using chlorpyrifos, thiacloprid and thiamethoxam by EU regulation, growers seek for information about the resistance of CPB to used insecticides and recommended antiresistant strategies. The development of CPB resistance to selected insecticides was evaluated in bioassays in 69 local populations from Czechia in 2017-2022 and in 2007-2022 in small plot experiments in Zabcice in South Moravia. The mortality in each subpopulation in the bioassays was evaluated at the field-recommended rates of insecticides to estimate the 50% and 90% lethal concentrations (LC50 and LC90, respectively). High levels of CPB resistance to lambda-cyhalothrin and chlorpyrifos were demonstrated throughout Czechia, without significant changes between years and regions. The average mortality after application of the field-recommended rate of lambda-cyhalothrin was influenced by temperature before larvae were sampled for bioassays and decreased with increasing temperature in June. Downwards trends in the LC90 values of chlorpyrifos and the average mortality after application of the field-recommended rate of acetamiprid in the bioassay were recorded over a 6-year period. The baseline LC50 value (with 95% confidence limit) of 0.04 mg/L of chlorantraniliprole was established for Czech populations of CPBs for the purpose of resistance monitoring in the next years. Widespread resistance to pyrethroids, organophosphates and neonicotinoids was demonstrated, and changes in anti-resistant strategies to control CPBs were discussed.

Does Leptinotarsa decemlineata larval survival after pesticide treatment depend on microbiome composition?

BACKGROUND

The microbiomes of some arthropods are believed to eliminate pesticides by chemical degradation or stimulation of the host immune system. The Colorado potato beetle (CPB; Leptinotarsa decemlineata) is an important agricultural pest with known resistance to used pesticides. We sought to analyze microbiome composition in CPB larvae from different sites and to identify the effect of pesticides on the microbiome of surviving and dead larvae after chlorpyrifos treatment in laboratory. Changes in the Lactococcus lactis community in larvae treated with chlorpyrifos and fed by potato leaves with L. lactis cover were studied by manipulative experiment. The microbiome was characterized by sequencing the 16S RNA gene.

RESULTS

The microbiome of L. decemlineata larvae is composed of a few operational taxonomic units (OTUs) (Enterobacteriaceae, Pseudocitrobacter, Acinetobacter, Pseudomonas, L. lactis, Enterococcus, Burkholderia and Spiroplasma leptinotarsae). The microbiome varied among the samples from eight sites and showed differences in profiles between surviving and dead larvae. The survival of larvae after chlorpyrifos treatment was correlated with a higher proportion of L. lactis sequences in the microbiome. The S. leptinotarsa profile also increased in the surviving larvae, but this OTU was not present in all sampling sites. In manipulative experiments, larvae treated with L. lactis had five-fold lower mortality rates than untreated larvae.

CONCLUSION

These results indicate that the microbiome of larvae is formed from a few bacterial taxa depending on the sampling site. A member of the gut microbiome, L. lactis, is believed to help overcome the toxic effects of chlorpyrifos in the larval gut. © 2023 Society of Chemical Industry.

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.