Comprehensive Detoxification Mechanism Assessment of Red Imported Fire Ant (Solenopsis invicta) against Indoxacarb

Entomopathogenic fungi in crops protection with an emphasis on bioactive metabolites and biological activities

Plant pathogens with their abundance are harmful and cause huge damage to different agricultural crops and economy of a country as well as lead towards the shortage of food for humans. For their management, the utilization of entomopathogenic fungi is an eco-friendly technique, sustainable to the environment, safe for humans and has promising effect over chemical-based pesticides. This process requires a biochemical mechanism, including the production of enzymes, toxins, and other metabolites that facilitate host infection and invasion. Essential enzymes such as chitinase, proteinase, and lipase play a direct role in breaking down the host cuticle, the primary barrier to EPF (Entomopathogenic Fungi) infection. Additionally, secondary metabolites such as destruxins in Metarhizium, beauvericin in Beauveria, hirsutellides in Hirsutella, isarolides in Isaria, cordyols in Cordyceps, and vertihemipterins in Verticillium, among others, act both directly and indirectly to disable the defense mechanisms of insect hosts, thereby accelerating the EPF infection process. The chemical composition of these secondary metabolites varies, ranging from simple non-peptide pigments such as oosporine to highly complex piperazine derivatives such as vertihemiptellides. The biocontrol efficacy of EPF is extensively studied, with numerous fungal strains commercially available on a large scale for managing arthropod pests. This review emphasizes the role of proteins and enzymes against crop pathogens, detailing their mode of action, and describing the metabolites from entomopathogenic fungi and their biological activities. In doing so, these findings contribute to establishing a symbiotic equilibrium between agricultural productivity and environmental conservation.

Behavioral and Transcriptomic Analyses in the Indoxacarb Response of a Non-Target Damselfly Species

Ischnura senegalensis, which widely spreads in paddy fields, has the potential to be used as a natural predator of insect pests. However, the application of insecticides in the field could pose a threat to the survival of I. senegalensis. Among these pesticides, indoxacarb, an oxadiazine insecticide, is renowned for its broad-spectrum efficacy against numerous insect pests. In this study, we examined the toxicity of indoxacarb towards the larvae of I. senegalensis. Behavioral experiments and transcriptome analyses were conducted under indoxacarb treatments. Results revealed that indoxacarb induced abnormal body gestures and significant locomotory impairments, which could ultimately reduce the survival rate of the larvae in their natural habitat. Moreover, transcriptome analyses indicated that genes related to muscle function were significantly affected. Interestingly, at lower concentrations of indoxacarb (0.004 mg/L), the larvae seem to detoxify the indoxacarb with the aid of the cytochrome P450 gene. However, under higher concentrations (0.4 mg/L), the sensory abilities of the larvae were significantly diminished, and they were unable to degrade the toxicity of indoxacarb. Our study underscores the importance of carefully evaluating the impact of insecticides on non-target predatory insects before their widespread application.

The function of microbial enzymes in breaking down soil contaminated with pesticides: a review

The use of pesticides and the subsequent accumulation of residues in the soil has become a worldwide problem. Organochlorine (OC) pesticides have spread widely in the environment and caused contamination from past agricultural activities. This article reviews the bioremediation of pesticide compounds in soil using microbial enzymes, including the enzymatic degradation pathway and the recent development of enzyme-mediated bioremediation. Enzyme-mediated bioremediation is divided into phase I and phase II, where the former increases the solubility of pesticide compounds through oxidation-reduction and hydrolysis reactions, while the latter transforms toxic pollutants into less toxic or nontoxic products through conjugation reactions. The identified enzymes that can degrade OC insecticides include dehalogenases, phenol hydroxylase, and laccases. Recent developments to improve enzyme-mediated bioremediation include immobilization, encapsulation, and protein engineering, which ensure its stability, recyclability, handling and storage, and better control of the reaction.

The Effect of Botanical Pesticides Azadirachtin, Celangulin, and Veratramine Exposure on an Invertebrate Species Solenopsis invicta (Hymenoptera: Formicidae)

The injudicious and excessive use of synthetic pesticides has deleterious effects on humans, ecosystems, and biodiversity. As an alternative to traditional crop-protection methods, botanical pesticides are gaining importance. In this research endeavor, we examined the contact toxicity, knockdown time, lethal time, and toxicity horizontal transmission of three natural pesticides from plants (azadirachtin, celangulin, and veratramine) on red imported fire ants (RIFA; Solenopsis invicta). Our research findings indicated that azadirachtin and celangulin exhibited relatively high toxicity, with median lethal dose (LD50) values of 0.200 and 0.046 ng/ant, respectively, whereas veratramine exhibited an LD50 value of 544.610 ng/ant for large workers of S. invicta at 24 h post-treatment. Upon treatment with 0.125 mg/L, the (median lethal time) LT50 values of azadirachtin and celangulin were determined to be 60.410 and 9.905 h, respectively. For veratramine, an LT50 value of 46.967 h was achieved after being tested with 200 mg/L. Remarkably, azadirachtin and celangulin were found to exhibit high horizontal transfer among RIFA, with high secondary mortality (100%) and tertiary mortalities (>61%) after 48 h of treatment with 250 mg/L, as well as with their dust formulations for 72 h. However, veratramine did not exhibit significant toxicity or horizontal transfer effects on RIFA, even at high concentrations. These findings suggest that azadirachtin and celangulin are likely to have a highly prominent potential in the management of S. invicta.

Enhancement of tolerance against flonicamid in Solenopsis invicta (Hymenoptera: Formicidae) through overexpression of CYP6A14

Solenopsis invicta is a main issue in southern China and is causing significant damage to the local ecological environment. The extensive use of insecticides has resulted in the development of tolerance in S. invicta. In our study, ten S. invicta colonies from Sichuan Province exhibited varying degrees of tolerance against flonicamid, with LC50 values from 0.49 mg/L to 8.54 mg/L. The sensitivity of S. invicta to flonicamid significantly increased after treatment with the P450 enzyme inhibitor piperonyl butoxide (PBO). Additionally, the activity of P450 in S. invicta was significantly enhanced after being treated with flonicamid. Flonicamid induced the expression levels of CYP4aa1, CYP9e2, CYP4C1, and CYP6A14. The expression levels of these P450 genes were significantly higher in the tolerant colonies compared to the sensitive colonies, and the relative copy numbers of CYP6A14 in the tolerant colonies were 2.01-2.15 fold. RNAi feeding treatment effectively inhibited the expression of P450 genes, thereby reducing the tolerance of S. invicta against flonicamid. In addition, the overexpression of CYP6A14 in D. melanogaster resulted in reduced sensitivity to flonicamid. Our investigations revealed hydrophobic interactions between flonicamid and seven amino acid residues of CYP6A14, along with the formation of a hydrogen bond between Glu306 and flonicamid. Our findings suggest that flonicamid can effectively control S. invicta and P450 plays a pivotal role in the tolerance of S. invicta against flonicamid. The overexpression of CYP6A14 also increased tolerance to flonicamid.

Foraging Behaviors of Red Imported Fire Ants (Hymenoptera Formicidae) in Response to Bait Containing Different Concentrations of Fipronil, Abamectin, or Indoxacarb

The red imported fire ant, Solenopsis invicta Buren, is a severe pest with agricultural, ecological, and medical significance. The baiting treatment is one of the main methods to control S. invicta. However, few studies have evaluated the acceptance of fire ant bait. Here, field and laboratory studies were conducted to investigate the foraging behaviors of S. invicta responding to fire ant baits containing different concentrations of active ingredients (fipronil, abamectin, or indoxacarb). Field studies showed that S. invicta transported significantly less 0.0125% fipronil bait than control bait (without toxicant) and 0.0001% fipronil bait. The number of foraging ants significantly decreased with an increase in fipronil concentration. Our previous study showed that S. invicta usually buries the food treated with repellent chemicals, and interestingly, significantly more soil particles were transported into tubes containing 0.0001% fipronil bait than tubes containing control bait or 0.0125% fipronil bait. In addition, S. invicta transported significantly less 0.0005% abamectin bait than control bait, and significantly fewer ants were found in tubes containing 0.0125% abamectin bait than control bait. However, there was no significant difference in bait transport, number of foraging ants, and weight of soil particles relocated in tubes containing different concentrations of indoxacarb bait. In addition, laboratory studies showed that S. invicta transported significantly less 0.0125% fipronil bait than control bait and bait containing abamectin (0.0025% or 0.0125%) or indoxacarb (0.0125% or 0.0625%). In addition, the transport speed for the 0.0125% fipronil bait was the slowest. These results show that specific concentrations of some active ingredients may negatively affect bait acceptance for S. invicta, and should be avoided in fire ant bait production.

Baccharis Species Essential Oils: Repellency and Toxicity against Yellow Fever Mosquitoes and Imported Fire Ants

Essential oils from five Baccharis species were screened for their toxicity and biting deterrence/repellency against yellow fever mosquito, Aedes aegypti (L.), and imported fire ants, including Solenopsis invicta Buren (RIFA), Solenopsis richteri Forel (BIFA) and their hybrids (HIFA). Baccharis microdonta DC. and B. punctulata DC. at 10 µg/cm2 showed biting deterrence similar to DEET, N, N-diethyl-meta-toluamide at 25 nmol/cm2, whereas the repellency of B. pauciflosculosa DC., B. sphenophylla Dusén ex Malme and B. reticularioides Deble & A.S. Oliveira essential oils was significantly lower than DEET against mosquitoes. Two major compounds from the active essential oils, kongol and spathulenol, also exhibited biting deterrence similar to DEET against mosquitoes. The highest toxicity exhibited against mosquitoes was by Baccharis punctulata essential oil (LC50 = 20.4 ppm), followed by B. pauciflosculosa (LC50 = 31.9 ppm), B. sphenophylla (LC50 = 30.8 ppm), B. microdonta (LC50 = 28.6 ppm), kongol (LC50 = 32.3 ppm), spathulenol (LC50 = 48.7 ppm) and B. reticularioides essential oil (LC50 = 84.4 ppm). Baccharis microdonta essential oil showed repellency against RIFA, BIFA and HIFA at 4.9, 4.9 and 39 µg/g, respectively. Baccharis microdonta essential oil also showed toxicity with LC50 of 78.9, 97.5 and 136.5 µg/g against RIFA, BIFA and HIFA, respectively, at 24 h post treatment.

Integrated mass spectrometry imaging and metabolomics reveals sublethal effects of indoxacarb on the red fire ant Solenopsis invicta

BACKGROUND

Indoxacarb, representing an efficient insecticide, is normally made into a bait to spread the poison among red fire ants so that it can be widely applied in the prevention and control of Solenopsis invicta. However, the potential toxicity mechanism of S. invicta in response to indoxacarb remains to be explored. In this study, we integrated mass spectrometry imaging (MSI) and untargeted metabolomics methods to reveal disturbed metabolic expression levels and spatial distribution within the whole-body tissue of S. invicta treated with indoxacarb.

RESULTS

Metabolomics results showed a significantly altered level of metabolites after indoxacarb treatment, such as carbohydrates, amino acids and pyrimidine and derivatives. Additionally, the spatial distribution and regulation of several crucial metabolites resulting from the metabolic pathway and lipids can be visualized using label-free MSI methods. Specifically, xylitol, aspartate, and uracil were distributed throughout the whole body of S. invicta, while sucrose-6'-phosphate and glycerol were mainly distributed in the abdomen of S. invicta, and thymine was distributed in the head and chest of S. invicta. Taken together, the integrated MSI and metabolomics results indicated that the toxicity mechanism of indoxacarb in S. invicta is closely associated with the disturbance in several key metabolic pathways, such as pyrimidine metabolism, aspartate metabolism, pentose and glucuronate interconversions, and inhibited energy synthesis.

CONCLUSION

Collectively, these findings provide a new perspective for the understanding of toxicity assessment between targeted organisms S. invicta and pesticides. © 2023 Society of Chemical Industry.

Regioselective Claisen-Schmidt Adduct of 2-Undecanone from Houttuynia cordata Thunb as Insecticide/Repellent against Solenopsis invicta and Repositioning Plant Fungicides against Colletotrichum fragariae

The U.S. Department of Agriculture (USDA) has established research programs to fight the phytopathogen Colletotrichum fragariae and the invasive red imported fire ant, Solenopsis invicta. C. fragariae is known to cause anthracnose disease in fruits and vegetables, while S. invicta is known for its aggressive behavior and painful stings and for being the cause of significant damage to crops, as well as harm to humans and animals. Many plants have been studied for potential activity against C. fragariae and S. invicta. Among the studied plants, Houttuynia cordata Thunb has been shown to contain 2-undecanone, which h is known for its antifungal activity against Colletotrichum gloesporioides. Based on the mean amount of sand removed, 2-undecanone showed significant repellency at 62.5 µg/g, similar to DEET (N,N-diethyl-meta-toluamide), against S. invicta. The 2-Undecanone with an LC50 of 44.59 µg/g showed toxicity against S. invicta workers. However, neither H. cordata extract nor 2-undecanone had shown activity against C. fragariae despite their known activity against C. gloesporioides, which in turn motivates us in repositioning 2-undecanone as a selected candidate for a Claisen-Schmidt condensation that enables access to several analogs (2a-f). Among the prepared analogs, (E)-1-(3-methylbenzo[b]thiophen-2-yl)dodec-1-en-3-one (2b) and (E)-1-(5-bromothiophen-2-yl)dodec-1-en-3-one (2f) showed promising activity against C. fragariae, revealing a distinctive structural activity relationship (SAR). The generated analogs revealed a clear regioselectivity pattern through forming the C=C alkene bond at position C-1. These data open the window for further lead optimization and product development in the context of managing C. fragariae and S. invicta.

Matricaria chamomilla Essential Oils: Repellency and Toxicity against Imported Fire Ants (Hymenoptera: Formicidae)

Matricaria chamomilla flower essential oils (EOs) blue Egyptian (EO-1), chamomile German CO2 (EO-2), and chamomile German (EO-3) and the pure compound α-bisabolol were evaluated against red imported fire ants (RIFA), Solenopsis invicta Buren, black imported fire ants, S. richteri Forel (BIFA), and hybrid imported fire ants (HIFA) for their repellency and toxicity. A series of serial dilutions were tested starting from 125 µg/g until the failure of the treatment. Based on the amount of sand removed, EO-1 showed significant repellency at dosages of 7.8, 7.8, and 31.25 µg/g against RIFA, BIFA, and HIFA, respectively. EO-3 was repellent at 3.9, 7.8, and 31.25 µg/g against BIFA, RIFA, and HIFA, whereas α-bisabolol was active at 7.8, 7.8, and 31.25 µg/g against BIFA, HIFA, and RIFA, respectively. DEET (N, N-diethyl-meta-toluamide) was active at 31.25 µg/g. Toxicity of EOs and α-bisabolol was mild to moderate. For EO-1, LC₅₀ values were 93.6 and 188.11 µg/g against RIFA and BIFA; 98.11 and 138.4 µg/g for EO-2; and 142.92 and 202.49 µg/g for EO-3, respectively. The LC₅₀ of α-bisabolol was 159.23 µg/g against RIFA. In conclusion, M. chamomilla EOs and α-bisabolol offer great potential to be developed as imported fire ant repellents.

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.

Efficacy of Matrine, Rotenone, and Pyrethrin Against Red Imported Fire Ant Solenopsis invicta (Hymenoptera: Formicidae) and Their Impact on Aquatic Organisms

Chemicals, including toxic bait and dusts, are the main means of controlling the red imported fire ant Solenopsis invicta (abbreviation 'RIFA'), which is a serious invasive pest. To identify environmentally friendly chemicals for controlling RIFA, we tested the toxicity and horizontal transfer of three botanical insecticides-matrine, rotenone, and pyrethrin-and their impact on aquatic organisms (i.e., three fish and one shrimp). The LD50 value of matrine, rotenone, and pyrethrin was 0.24, 50.929, and 13.590 ng/ant, respectively. Matrine, rotenone, and pyrethrin had effective horizontal transfer and caused significant secondary mortality. After exposure to donor workers, 90.75%, 90.75%, and 100% of recipient workers in the 0.025% matrine, 1.0% rotenone, and 0.3% pyrethrin dust treatments, respectively, died within 48 h. Furthermore, 0.025% matrine dust caused significant tertiary mortality (49.5%). Tertiary mortality caused by 1.0% rotenone and 0.3% pyrethrin dusts was very low, only 7.75% and 18.5%, respectively. In a field trial, the comprehensive mortality effect of 0.05% matrine, 1.50% rotenone, and 0.375% pyrethrin dust was 74.96%, 30.10%, and 29.27%, respectively, after 14 d of treatment. Matrine had low toxicity to the fish Hypophthalmichthys molitrix, and 37.5 mg/L pyrethrin had low toxicity to the fish Cirrhinus molitorella, H. molitrix, and Oreochromis niloticus. However, rotenone was highly toxic to all three fish. The shrimp Neocaridina denticulate was not sensitive to matrine, rotenone, or pyrethrin. Matrine dust has highly effective horizontal transfer, and 0.05% matrine dust has great potential for managing RIFA in organic farms, aquaculture farms of H. molitrix, and water resource regions.

Transcriptome analysis reveals differential effects of beta-cypermethrin and fipronil insecticides on detoxification mechanisms in Solenopsis invicta

Insecticide resistance poses many challenges in insect pest control, particularly in the control of destructive pests such as red imported fire ants (Solenopsis invicta). In recent years, beta-cypermethrin and fipronil have been extensively used to manage invasive ants, but their effects on resistance development in S. invicta are still unknown. To investigate resistance development, S. invicta was collected from populations in five different cities in Guangdong, China. The results showed 105.71- and 2.98-fold higher resistance against fipronil and beta-cypermethrin, respectively, in the Guangzhou population. The enzymatic activities of acetylcholinesterase, carboxylases, and glutathione S-transferases significantly increased with increasing beta-cypermethrin and fipronil concentrations. Transcriptomic analysis revealed 117 differentially expressed genes (DEGs) in the BC-ck vs. BC-30 treatments (39 upregulated and 78 downregulated), 109 DEGs in F-ck vs. F-30 (33 upregulated and 76 downregulated), and 499 DEGs in BC-30 vs. F-30 (312 upregulated and 187 downregulated). Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that DEGs associated with insecticide resistance were significantly enriched in metabolic pathways, the AMPK signaling pathway, the insulin signaling pathway, carbon metabolism, peroxisomes, fatty acid metabolism, drug metabolism enzymes and the metabolism of xenobiotics by cytochrome P450. Furthermore, we found that DEGs important for insecticide detoxification pathways were differentially regulated under both insecticide treatments in S. invicta. Comprehensive transcriptomic data confirmed that detoxification enzymes play a significant role in insecticide detoxification and resistance development in S. invicta in Guangdong Province. Numerous identified insecticide-related genes, GO terms, and KEGG pathways indicated the resistance of S. invicta workers to both insecticides. Importantly, this transcriptome profile variability serves as a starting point for future research on insecticide risk evaluation and the molecular mechanism of insecticide detoxification in invasive red imported fire ants.

Toxicity, horizontal transfer, and physiological and behavioral effects of cycloxaprid against Solenopsis invicta (Hymenoptera: Formicidae)

BACKGROUND

The red imported fire ant, Solenopsis invicta Buren, is a significant urban, agricultural, and medical pest with a wide distribution in the world. Surface or mound treatment using contact insecticide is one of the main methods to control S. invicta. In the present study, cycloxaprid, a newly discovered neonicotinoid insecticide, was evaluated for S. invicta control and compared with two referent insecticides, imidacloprid and bifenthrin.

RESULTS

Surfaces or sand treated with cycloxaprid, imidacloprid, or bifenthrin caused high mortality of S. invicta workers, and the action of cycloxaprid or imidacloprid was slower than bifenthrin. Like imidacloprid and bifenthrin, cycloxaprid can be horizontally transferred from corpses or live donor ants to recipient ants. In addition, cycloxaprid- or imidacloprid-treated surfaces significantly induced the activities of acetylcholinesterase (AChE) and detoxification enzymes; nevertheless, they had no significant effect on the foraging behaviors of S. invicta workers. Also, sand treated with cycloxaprid or imidacloprid did not negatively affect the digging activities of ants. Interestingly, S. invicta workers excavated significantly more sand containing 0.01 mg/kg cycloxaprid than untreated sand in the no-choice digging bioassays. In addition, extensive nesting activities (sand excavation and stacking) were observed in the flowerpots containing untreated sand or sand treated with cycloxaprid or imidacloprid. On the contrary, bifenthrin significantly reduced the foraging, digging, and nesting activities of S. invicta workers.

CONCLUSION

Cycloxaprid is a slow-acting and nonrepellent insecticide against S. invicta workers, and its contact and horizontal toxicities are slightly higher than imidacloprid. © 2022 Society of Chemical Industry.

Role of Insect Gut Microbiota in Pesticide Degradation: A Review

Insect pests cause significant agricultural and economic losses to crops worldwide due to their destructive activities. Pesticides are designed to be poisonous and are intentionally released into the environment to combat the menace caused by these noxious pests. To survive, these insects can resist toxic substances introduced by humans in the form of pesticides. According to recent findings, microbes that live in insect as symbionts have recently been found to protect their hosts against toxins. Symbioses that have been formed are between the pests and various microbes, a defensive mechanism against pathogens and pesticides. Insects' guts provide unique conditions for microbial colonization, and resident bacteria can deliver numerous benefits to their hosts. Insects vary significantly in their reliance on gut microbes for basic functions. Insect digestive tracts are very different in shape and chemical properties, which have a big impact on the structure and composition of the microbial community. Insect gut microbiota has been found to contribute to feeding, parasite and pathogen protection, immune response modulation, and pesticide breakdown. The current review will examine the roles of gut microbiota in pesticide detoxification and the mechanisms behind the development of resistance in insects to various pesticides. To better understand the detoxifying microbiota in agriculturally significant pest insects, we provided comprehensive information regarding the role of gut microbiota in the detoxification of pesticides.