Characterization of an agmatine N-acetyltransferase from Bactrocera dorsalis that modulates ovary development.

Agmatine N-acetyltransferase (AgmNAT), which catalyzes the formation of N-acetylagmatine from acetyl-CoA and agmatine, is a member of the GCN5-related N-acetyltransferase family. So far, knowledge of the physiological roles of AgmNAT in insects is limited. Here, we identified one gene encoding protein homologous to that of Drosophila AgmNAT using sequence information from an activity-verified Drosophila AgmNAT in a BLAST search of the Bactrocera dorsalis genome. We expressed and purified B. dorsalis AgmNAT in Escherichia coli and used the purified enzyme to define the substrate specificity for acyl-CoA and amine substrates. Our application of the screening strategy to BdorAgmNAT led to the identification of agmatine as the best amine substrate for this enzyme, with the highest kcat/Km value. We successfully obtained a BdorAgmNAT knockout strain based on a wild-type strain (WT) using the CRISPR/Cas9 technique. The ovary development of the BdorAgmNAT knockout mutants was delayed for 10 days compared with the WT specimens. Moreover, mutants had a much smaller mature ovary size and laid far fewer eggs than WT. Loss of function of BdorAgmNAT caused by RNAi with mature WT females did not affect their fecundity. These findings indicate that BdorAgmNAT is critical for oogenesis. Our data provide the first evidence for AgmNAT in regulating ovary development.

Toxicity of Beauveria bassiana to Bactrocera dorsalis and effects on its natural predators.

Entomopathogenic fungi (EPF) are economical and environmentally friendly, forming an essential part of integrated pest management strategies. We screened six strains of Beauveria bassiana (B1-B6) (Hypocreales: Cordycipitaceae), of which B4 was the most virulent to Bactrocera dorsalis (Hendel) (Diptera: Tephritidae). We further assessed the biological characteristics of strain B4 and the environmental factors influencing its ability to infect B. dorsalis. We also evaluated the effects of B4 on two of the natural predators of B. dorsalis. We found that strain B4 was the most virulent to 3rd instar larvae, pupae, and adult B. dorsalis, causing mortality rates of 52.67, 61.33, and 90.67%, respectively. B4 was not toxic to B. dorsalis eggs. The optimum B4 effects on B. dorsalis were achieved at a relative humidity of 91-100% and a temperature of 25°C. Among the six insecticides commonly used for B. dorsalis control, 1.8% abamectin emulsifiable concentrate had the strongest inhibitory effect on B4 strain germination. B4 spraying affected both natural enemies (Amblyseius cucumeris and Anastatus japonicus), reducing the number of A. cucumeris and killing A. japonicus adults. We found a valuable strain of EPF (B4) that is virulent against many life stages of B. dorsalis and has great potential for the biological control of B. dorsalis. We also provide an important theoretical and practical base for developing a potential fungicide to control B. dorsalis.

Effect of entomopathogenic fungi on behavior and physiology of Solenopsis invicta (Hymenoptera, Formicidae).

In an ant colony, a large number of nestmates with a similar gene pool coexist, making them more vulnerable to pathogenic attacks. These pathogens influence the behavior and physiology of the fire ant Solenopsis invicta Buren. Here, we evaluated the impact of entomopathogenic fungi (EPF) Metarhizium anisopliae on the behavior (locomotion and foraging) and physiology (biological molecules, anti-fungal activity, and survival) of S. invicta. Distance traveled and velocity significantly decreased, while turn angle and angular velocity significantly increased in ants exposed to a higher concentration of M. anisopliae compared to ants exposed to control after 36 h, which showed disturbed locomotion. Fungus infection significantly affected the foraging behavior of ants. Fungus-exposed ants spent significantly less time in the food zone (area with food) than in the inner zone (area without food). The activities of 4 enzymes, peroxidase, glutathione-S-transferase, hydrogen peroxide (H2O2), and carboxylesterase were significantly decreased. In contrast, catalase and anti-fungal activities were increased after fungal exposure compared to the control. The activity of acetylcholinesterase, which hydrolyses the important neurotransmitter acetylcholine, also decreased after fungal application compared to the control. Survival of ants was also significantly reduced after fungus infection compared to the control. Our findings help to understand the influence of M. anisopliae on the behavior and physiology of S. invicta, which will help in the management of S. invicta using the EPF M. anisopliae.

Lactic acid bacteria modulate the CncC pathway to enhance resistance to ß-cypermethrin in the oriental fruit fly.

The gut microbiota of insects has been shown to regulate host detoxification enzymes. However, the potential regulatory mechanisms involved remain unknown. Here, we report that gut bacteria increase insecticide resistance by activating the cap "n" collar isoform-C (CncC) pathway through enzymatically generated reactive oxygen species (ROS) in Bactrocera dorsalis. We demonstrated that Enterococcus casseliflavus and Lactococcus lactis, two lactic acid-producing bacteria, increase the resistance of B. dorsalis to ß-cypermethrin by regulating cytochrome P450 (P450) enzymes and α-glutathione S-transferase (GST) activities. These gut symbionts also induced the expression of CncC and muscle aponeurosis fibromatosis. BdCncC knockdown led to a decrease in resistance caused by gut bacteria. Ingestion of the ROS scavenger vitamin C in resistant strain affected the expression of BdCncC/BdKeap1/BdMafK, resulting in reduced P450 and GST activity. Furthermore, feeding with E. casseliflavus or L. lactis showed that BdNOX5 increased ROS production, and BdNOX5 knockdown affected the expression of the BdCncC/BdMafK pathway and detoxification genes. Moreover, lactic acid feeding activated the ROS-associated regulation of P450 and GST activity. Collectively, our findings indicate that symbiotic gut bacteria modulate intestinal detoxification pathways by affecting physiological biochemistry, thus providing new insights into the involvement of insect gut microbes in the development of insecticide resistance.

Decoding epitranscriptomic regulation of viral infection: mapping of RNA N6-methyladenosine by advanced sequencing technologies.

Elucidating the intricate interactions between viral pathogens and host cellular machinery during infection is paramount for understanding pathogenic mechanisms and identifying potential therapeutic targets. The RNA modification N6-methyladenosine (m6A) has emerged as a significant factor influencing the trajectory of viral infections. Hence, the precise and quantitative mapping of m6A modifications in both host and viral RNA is pivotal to understanding its role during viral infection. With the rapid advancement of sequencing technologies, scientists are able to detect m6A modifications with various quantitative, high-resolution, transcriptome approaches. These technological strides have reignited research interest in m6A, underscoring its significance and prompting a deeper investigation into its dynamics during viral infections. This review provides a comprehensive overview of the historical evolution of m6A epitranscriptome sequencing technologies, highlights the latest developments in transcriptome-wide m6A mapping, and emphasizes the innovative technologies for detecting m6A modification. We further discuss the implications of these technologies for future research into the role of m6A in viral infections.

Distribution analysis of TRH in Bactrocera dorsalis using a CRISPR/Cas9-mediated reporter knock-in strain.

Although the study of many genes and their protein products is limited by the availability of high-quality antibodies, this problem could be solved by fusing a tag/reporter to an endogenous gene using a gene-editing approach. The type II bacterial CRISPR/Cas system has been demonstrated to be an efficient gene-targeting technology for many insects, including the oriental fruit fly Bactrocera dorsalis. However, knocking in, an important editing method of the CRISPR/Cas9 system, has lagged in its application in insects. Here, we describe a highly efficient homology-directed genome editing system for B. dorsalis that incorporates coinjection of embryos with Cas9 protein, guide RNA and a short single-stranded oligodeoxynucleotide donor. This one-step procedure generates flies carrying V5 tag (42 bp) in the BdorTRH gene. In insects, as in other invertebrates and in vertebrates, the neuronal tryptophan hydroxylase (TRH) gene encodes the rate-limiting enzyme for serotonin biosynthesis in the central nervous system. Using V5 monoclonal antibody, the distribution of TRH in B. dorsalis at different developmental stages was uncovered. Our results will facilitate the generation of insects carrying precise DNA inserts in endogenous genes and will lay foundation for the investigation of the neural mechanisms underlying the serotonin-mediated behaviour of B. dorsalis.

Reproductive behavior of fruit flies: courtship, mating, and oviposition.

Many species of the Tephritidae family are invasive and cause huge damage to agriculture and horticulture, owing to their reproductive characteristics. In this review, we have summarized the existing studies on the reproductive behavior of Tephritidae, particularly those regarding the genes and external factors that are associated with courtship, mating, and oviposition. Furthermore, we outline the issues that still need to be addressed in fruit fly reproduction research. The review highlights the implications for understanding the reproductive behavior of fruit flies and discusses methods for their integrated management and biological control. © 2023 Society of Chemical Industry.

Juvenile hormone induces reproduction via miR-1175-3p in the red imported fire ant, Solenopsis invicta.

Juvenile hormone (JH) acts in the regulation of caste differentiation between queens and workers (i.e., with or without reproductive capacity) during vitellin synthesis and oogenesis in social insects. However, the regulatory mechanisms have not yet been elucidated. Here, we identified a highly expressed microRNA (miRNA), miR-1175-3p, in the red imported fire ant, Solenopsis invicta. We found that miR-1175-3p is prominently present in the fat bodies and ovaries of workers. Furthermore, miR-1175-3p interacts with its target gene, broad-complex core (Br-C), in the fat bodies. By utilizing miR-1175-3p agomir, we successfully suppressed the expression of the Br-C protein in queens, resulting in reduced vitellogenin expression, fewer eggs, and poorly developed ovaries. Conversely, decreasing miR-1175-3p levels led to the increased expression of Br-C and vitellogenin in workers, triggering the "re-development" of the ovaries. Moreover, when queens were fed with JH, the expression of miR-1175-3p decreased, whereas the expression of vitellogenin-2 and vitellogenin-3 increased. Notably, the suppression of fertility in queens caused by treatment with agomir miR-1175-3p was completely rescued by the increased vitellogenin expression induced by being fed with JH. These results suggest the critical role of miR-1175-3p in JH-regulated reproduction, shedding light on the molecular mechanism underlying miRNA-mediated fecundity in social insects and providing a novel strategy for managing S. invicta.

Transcriptomic Analysis of Metarhizium anisopliae-Induced Immune-Related Long Non-Coding RNAs in Polymorphic Worker Castes of Solenopsis invicta.

Long non-coding RNAs (lncRNAs) represent a class of RNA molecules that do not encode proteins. Generally studied for their regulatory potential in model insects, relatively little is known about their immunoregulatory functions in different castes of eusocial insects, including Solenopsis invicta, a notoriously invasive insect pest. In the current study, we used Metarhizium anisopliae, an entomopathogenic fungus, to infect the polymorphic worker castes (Major and Minor Workers) and subjected them to RNA sequencing at different intervals (6, 24, and 48 h post-infection (hpi)). Comprehensive bioinformatic analysis identified 5719 (1869 known and 3850 novel) lncRNAs in all libraries. Genomic characteristics analysis showed that S. invicta lncRNAs exhibited structural similarities with lncRNAs from other eusocial insects, including lower exon numbers, shorter intron and exon lengths, and a lower expression profile. A comparison of lncRNAs in major and minor worker ants revealed that several lncRNAs were exclusively expressed in one worker caste and remained absent in the other. LncRNAs such as MSTRG.12029.1, XR_005575440.1 (6 h), MSTRG.16728.1, XR_005575440.1 (24 h), MSTRG.20263.41, and MSTRG.11994.5 (48 h) were only present in major worker ants, while lncRNAs such as MSTRG.8896.1, XR_005574239.1 (6 h), MSTRG.20289.8, XR_005575051.1 (24 h), MSTRG.20289.8, and MSTRG.6682.1 (48 h) were only detected in minor workers. Additionally, we performed real-time quantitative PCR and experimentally validated these findings. Functional annotation of cis-acting lncRNAs in major worker ants showed that lncRNAs targeted genes such as serine protease, trypsin, melanization protease-1, spaetzle-3, etc. In contrast, apoptosis and autophagy-related genes were identified as targets of lncRNAs in minor ants. Lastly, we identified several lncRNAs as precursors of microRNAs (miRNAs), such as miR-8, miR-14, miR-210, miR-6038, etc., indicating a regulatory relationship between lncRNAs, miRNAs, and mRNAs in antifungal immunity. These findings will serve as a genetic resource for lncRNAs in polymorphic eusocial ants and provide a theoretical basis for exploring the function of lncRNAs from a unique and novel perspective.

Transcriptomic Analysis Reveals the Impact of the Biopesticide Metarhizium anisopliae on the Immune System of Major Workers in Solenopsis invicta.

The red imported fire ant (Solenopsis invicta Buren, 1972) is a globally significant invasive species, causing extensive agricultural, human health, and biodiversity damage amounting to billions of dollars worldwide. The pathogenic fungus Metarhizium anisopliae (Metchnikoff) Sorokin (1883), widely distributed in natural environments, has been used to control S. invicta populations. However, the interaction between M. anisopliae and the immune system of the social insect S. invicta remains poorly understood. In this study, we employed RNA-seq to investigate the effects of M. anisopliae on the immune systems of S. invicta at different time points (0, 6, 24, and 48 h). A total of 1313 differentially expressed genes (DEGs) were identified and classified into 12 expression profiles using short time-series expression miner (STEM) for analysis. Weighted gene co-expression network analysis (WGCNA) was employed to partition all genes into 21 gene modules. Upon analyzing the statistically significant WGCNA model and conducting Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis on the modules, we identified key immune pathways, including the Toll and Imd signaling pathways, lysosomes, autophagy, and phagosomes, which may collectively contribute to S. invicta defense against M. anisopliae infection. Subsequently, we conducted a comprehensive scan of all differentially expressed genes and identified 33 immune-related genes, encompassing various aspects such as recognition, signal transduction, and effector gene expression. Furthermore, by integrating the significant gene modules derived from the WGCNA analysis, we constructed illustrative pathway diagrams depicting the Toll and Imd signaling pathways. Overall, our research findings demonstrated that M. anisopliae suppressed the immune response of S. invicta during the early stages while stimulating its immune response at later stages, making it a potential biopesticide for controlling S. invicta populations. These discoveries lay the foundation for further understanding the immune mechanisms of S. invicta and the molecular mechanisms underlying its response to M. anisopliae.

Effect of fertilization on the degradation and enantioselectivity of fipronil in soil.

BACKGROUND: Fertilizers and pesticides are commonly used simultaneously in agriculture. However, the effects of common fertilizers on the dissipation, enantioselectivity, and metabolites of the chiral insecticide fipronil in soil are yet to be reported. RESULT: An enantioselective method for detecting fipronil enantiomers and their metabolites in different soil matrices was developed using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The results showed that organic and compound fertilizers significantly decreased the degradation of S- and R-fipronil, whereas phosphate and microbial fertilizers slightly reduced fipronil dissipation. The half-life values for S- and R-fipronil were 43.3 and 28.9 days, 99.0 and 63.0 days, 69.3 and 43.3 days, 46.2 and 30.1 days, and 43.3 and 31.5 days, respectively, in the control and the four fertilizer treatments, respectively. The enantioselectivity of fipronil enantiomers occurred and R-fipronil exhibited preferential degradation with an enantiomeric fraction (EF) of 0.4900-0.6238 in all treatments; but the four tested fertilizers decreased enantioselectivity with EF values changed from 0.4970 to 0.6238 in the control to 0.4900-0.6171 in fertilizer treatments. Two metabolites, fipronil sulfone and sulfide, were produced, and their amounts increased with culture time in all treatments. Fertilization reduced the content of fipronil sulfide and sulfone but hardly reduced the total amount of fipronil and its metabolites. CONCLUSION: Fertilizers affect the environmental behavior of fipronil in the soil. Fertilization alters the soil bacterial community, which may be an important factor. This influence is relatively complicated and should be comprehensively considered in the environmental risk assessment of pesticides. © 2023 Society of Chemical Industry.

Differences in rectal amino acid levels determine bacteria-originated sex pheromone specificity in two closely related flies.

Sex pheromones are widely used by insects as a reproductive isolating mechanism to attract conspecifics and repel heterospecifics. Although researchers have obtained extensive knowledge about sex pheromones, little is known about the differentiation mechanism of sex pheromones in closely related species. Using Bactrocera dorsalis and Bactrocera cucurbitae as the study model, we investigated how the male-borne sex pheromones are different. The results demonstrated that both 2,3,5-trimethylpyrazine (TMP) and 2,3,5,6-tetramethylpyrazine (TTMP) were sex pheromones produced by rectal Bacillus in the two flies. However, the TMP/TTMP ratios were reversed, indicating sex pheromone specificity in the two flies. Bacterial fermentation results showed that different threonine and glycine levels were responsible for the preference of rectal Bacillus to produce TMP or TTMP. Accordingly, threonine (glycine) levels and the expression of the threonine and glycine coding genes were significantly different between B. dorsalis and B. cucurbitae. In vivo assays confirmed that increased rectal glycine and threonine levels by amino acid feeding could significantly decrease the TMP/TTMP ratios and result in significantly decreased mating abilities in the studied flies. Meanwhile, decreased rectal glycine and threonine levels due to RNAi of the glycine and threonine coding genes was found to significantly increase the TMP/TTMP ratios and result in significantly decreased mating abilities. The study contributes to the new insight that insects and their symbionts can jointly regulate sex pheromone specificity in insects, and in turn, this helps us to better understand how the evolution of chemical communication affects speciation.

Rapid cold hardening and cold acclimation promote cold tolerance of oriental fruit fly, Bactrocera dorsalis (Hendel) by physiological substances transformation and cryoprotectants accumulation.

Insect response to cold stress is often associated with adaptive strategies and chemical variation. However, low-temperature domestication to promote the cold tolerance potential of Bactrocera dorsalis and transformation of main internal substances are not clear. Here, we use a series of low-temperature exposure experiments, supercooling point (SCP) measurement, physiological substances and cryoprotectants detection to reveal that pre-cooling with milder low temperatures (5 and 10°C) for several hours (rapid cold hardening) and days (cold acclimation) can dramatically improve the survival rate of adults and pupae under an extremely low temperature (-6.5°C). Besides, the effect of rapid cold hardening for adults could be maintained even 4 h later with 25°C exposures, and SCP was significantly declined after cold acclimation. Furthermore, content of water, fat, protein, glycogen, sorbitol, glycerol and trehalose in bodies were measured. Results showed that water content was reduced and increased content of proteins, glycogen, glycerol and trehalose after two cold domestications. Our findings suggest that rapid cold hardening and cold acclimation could enhance cold tolerance of B. dorsalis by increasing proteins, glycerol, trehalose and decreasing water content. Conclusively, identifying a physiological variation will be useful for predicting the occurrence and migration trend of B. dorsalis populations.

Lethal and sublethal effects of broflanilide on four tephritid pests (Diptera: Tephritidae).

BACKGROUND: Fruit flies are internationally important quarantine or invasive pests of many fruits and vegetables and can cause serious economic losses. Long-term reliance on insecticides for controlling these pests has led to increasing resistance to multiple insecticides; hence, a new agent is needed. In this study, the acute toxicity and sublethal effects of the novel insecticide broflanilide on four adult fruit fly species, Bactrocera dorsalis, Bactrocera cucurbitae, Bactrocera tau, and Bactrocera correcta, were evaluated. RESULTS: Broflanilide was effective against B. dorsalis and B. correcta, with lethal concentration values (amount required to kill 50% of animals; LC50 ) of 0.390 and 1.716 mg/L. However, for B. cucurbitae (19.673 mg/L) and B. tau (24.373 mg/L), the LC50 was 50-60 times higher than that of B. dorsalis. The survival rates of B. correcta and B. cucurbitae were significantly lower under LC50 treatment than those of the control (corrected for mortality rate). Sublethal concentrations of broflanilide stimulated fecundity in all species except B. tau. The hatching rate at LC50 was significantly lower for B. correcta and B. tau compared with the control and even more so for B. correcta, which was zero. CONCLUSION: Broflanilide is potentially an effective insecticide for controlling B. dorsalis and B. correcta. However, the variation in toxicity of broflanilide to the four fruit flies suggests that species variation needs to be carefully considered. Our results highlight the importance of clarifying the sublethal effects of insecticides on target insects to ensure the comprehensive evaluation and rational use of insecticides. © 2023 Society of Chemical Industry.

Protein feeding mediates sex pheromone biosynthesis in an insect.

Protein feeding is critical for male reproductive success in many insect species. However, how protein affects the reproduction remains largely unknown. Using Bactrocera dorsalis as the study model, we investigated how protein feeding regulated sex pheromone synthesis. We show that protein ingestion is essential for sex pheromone synthesis in male. While protein feeding or deprivation did not affect Bacillus abundance, transcriptome analysis revealed that sarcosine dehydrogenase (Sardh) in protein-fed males regulates the biosynthesis of sex pheromones by increasing glycine and threonine (sex pheromone precursors) contents. RNAi-mediated loss-of-function of Sardh decreases glycine, threonine, and sex pheromone contents and results in decreased mating ability in males. The study links male feeding behavior with discrete patterns of gene expression that plays role in sex pheromone synthesis, which in turn translates to successful copulatory behavior of the males.

Gut Microbiome Composition of the Fire Ant Solenopsis invicta: an Integrated Analysis of Host Genotype and Geographical Distribution.

Gut symbiotic bacteria are known to be closely related to insect development, nutrient metabolism, and disease resistance traits, but the most important factors leading to changes in these communities have not been well clarified. To address this, we examined the associations between the gut symbiotic bacteria and the host genotype and geographical distribution of Solenopsis invicta in China, where it is invasive and has spread primarily by human-mediated dispersal. Thirty-two phyla were detected in the gut symbiotic bacteria of S. invicta. Proteobacteria were the most dominant group among the gut symbiotic bacteria. Furthermore, the Bray-Curtis dissimilarity matrices of the gut symbiotic bacteria were significantly positively correlated with the geographical distance between the host ant colonies, but this relationship was affected by the social form. The distance between monogyne colonies had a significant effect on the Bray-Curtis dissimilarity matrices of gut symbiotic bacteria, but the distance between polygyne colonies did not. Moreover, the Bray-Curtis dissimilarity matrices were positively correlated with Nei's genetic distance of the host but were not correlated with the COI-based genetic distance. This study provides a scientific basis for further understanding the ecological adaptability of red imported fire ants during invasion and dispersal. IMPORTANCE We demonstrated that gut microbiota composition and diversity varied among populations. These among-population differences were associated with host genotype and geographical distribution. Our results suggested that population-level differences in S. invicta gut microbiota may depend more on environmental factors than on host genotype.

Surveillance and invasive risk of the red imported fire ant, Solenopsis invicta Buren in China.

BACKGROUND: The red imported fire ant, Solenopsis invicta Buren is one of the world's most successful and destructive invasive ant species. In mainland China, fast, monthly and annual pest reports on all pests have been established since 2010. The distribution of S. invicta resulting from climate change in China was predicted using MaxEnt modeling in combination with comprehensive surveillance data and 56 environmental factors. RESULTS: The fast and monthly reports revealed that S. invicta had spread to new territories almost every year in this timeframe. The transportation of seedlings and deployment of turfgrass were the major artificial transmission pathways. Annual reports indicated that control efforts had effectively reduced its occurrence areas and degree of severity of infestations, and retrieved the economic loss caused by S. invicta. The MaxEnt model predicted that S. invicta would expand to 23 provinces in China as a result of climate change. Moisture variables were the key factors affecting the distribution of this pest. CONCLUSION: Based on the theoretical reference framework of this research, China proposed the first-ever integrated tactics against a single pest, jointly involving nine ministries, which include clarifying responsibilities, cutting off transmission pathways, strengthening surveillance, declaring pest distributions and conducting preventive and control campaigns. Practical efforts and measures combating the devastation of S. invicta may shed light on its management and other invasive species worldwide. © 2022 Society of Chemical Industry.

The Effects of Nine Compounds on Aldehyde-Oxidase-Related Genes in Bactrocera dorsalis (Hendel).

Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) (B. dorsalis) is an important agricultural, major invasive, and quarantine pest that can cause significant damage to the economic value of the fruit and vegetable industry. Male bait is one of the most effective methods of surveying, monitoring, and controlling B. dorsalis. In our study, we constructed cDNA libraries using total RNA extracted independently from the antennae, mouthparts, and thoracic legs of male and female adults and the ovipositors of female adults and screened out four aldehyde-oxidase-related genes (AOX-related), C58800, C66700, C67485, and C67698. Molecular docking predictions showed that eight compounds, including 3,4-dimethoxycinnamyl alcohol, 3,4-dimethoxy-cinnamaldehyde, deet, ethyl N-acetyl-N-butyl-ß-alaninate, n-butyl butyrate, n-butyl butyrate, ethyl butyrate, methyl eugenol, and ethyl acetate, could combine with proteins encoded by the four B. dorsalis AOX-related genes. Furthermore, QPCR was performed to confirm that four compounds, including 3,4-dimethoxy cinnamic aldehyde, butyl levulinic acid ethyl ester (mosquito repellent), butyl butyrate, and methyl eugenol, induced significant changes in the AOX-related genes of B. dorsalis. These results provide useful information and guidance for the batch screening of potentially useful compounds and the search for effective attractants of B. dorsalis.

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.

Toxicity of Some Essential Oils Constituents against Oriental Fruit Fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae).

The massive use of synthetic pesticides to manage agricultural pests results in environmental pollution and health hazards. The secondary plant metabolites, which are majorly dominated by terpenoids, have the potential to be developed into novel alternatives to synthetic chemicals. Therefore, in our current investigation, six majorly dominated essential oil constituents were evaluated for their toxicity against adults and immature stages of oriental fruit flies, Bactrocera dorsalis, a worldwide fruit pest. The results indicated that carvacrol was the most toxic essential oil constituent (EOC) to adult flies, with LC50 of 19.48 mg/mL via fumigant assay, followed by thujone 75% mortality via ingestion toxicity test against adult fruit flies. Similarly, when larvae were dipped in different concentrations of EOCs, carvacrol appeared as the most toxic EOC with the lowest LC50 (29.12 mg/mL), followed by (-)-alpha-pinene (26.54 mg/mL) and (R)-(+)-limonene (29.12 mg/mL). In the oviposition deterrence tests, no egg was observed on oranges seedlings treated with 5% of each EOC (100% repellency). Regarding the repellency assay, a significantly higher number of flies (77%) were repelled from the Y-tube olfactometer arm containing (-)-alpha-pinene, followed by carvacrol (76%). Our results showed that the selected essential oil constituent has the potential to be developed as an alternative to synthetic pesticides against B. dorsalis. However, further research is required to assess the activities of these EOCs under open-field conditions.