Development Of Pesticide Resistance Research Articles

Isolation of Clonostachys rosea and Characterizing Its Entomopathogenic Activity against Dubas Bug (Ommatissus lybicus) Nymphs and Adults

The Dubas bug is a serious and widespread pest of date palms in several countries in the Middle East. Chemical pesticides are widely used for managing this pest; however, most pesticides fail due to the continuous development of pesticide resistance. The primary goal of this research was to isolate endophytic fungi and test their entomopathogenic activity against Dubas bug nymphs and adults. A total of 27 fungal isolates were obtained and identified using the nuc rDNA internal transcribed spacer (ITS1-5.8S-ITS2 = ITS) region. These strains represent 16 species, belonging to 10 genera of seven different families, Ascomycota with six families and Basidiomycota with a single family, Quambalariaceae. Due to its remarkable biological control ability against insect pests, Clonostachys rosea was further studied for its entomopathogenic activity against Ommatissus lybicus nymphs and adults in comparison to a commercial strain of Beauveria bassiana. The concentration of 1 × 108 conidia/mL of the selected endophytic isolate was used in lab experiments targeting Dubas bug healthy nymphs and adults. After 7 days of C. rosea treatment, the isolate caused significant mortality rates of 85% in the adult insects, while the mortality rates were moderate in the nymphs (33%). The commercial strain of B. bassiana resulted in 100% mortality levels in nymphs and adults of the Dubas bug. Scanning electron microscopy (SEM) of O. lybicus adults treated with C. rosea and B. bassiana showed mycelium growing on the eye, antenna, cuticle, and egg oviposition parts of O. lybicus. Mycelium growth of both fungi was also evident on the nymphs. This study reports for the first time the isolation of C. rosea from the Dubas bug, and its high entomopathogenic activity against an adult population of O. lybicus.

Can a Mixture of Farnesene Isomers Avert the Infestation of Aphids in Sugar Beet Crops?

The negative impact of pesticides on the environment and the potential of pest species to develop pesticide resistance make it necessary to explore new methods of pest control. Pheromones and other behavior-modifying semiochemicals are already important in integrated pest management (IPM). (E)-ß-farnesene (EBF) is a semiochemical that acts as an alarm pheromone in aphids. Upon perception of EBF, aphids stop feeding, move away, and sometimes even abandon the host plant. The aphids Myzus persicae and Aphis fabae are significant crop pests and vectors of many harmful phytopathogens affecting sugar beet (Beta vulgaris). Field trials were conducted at different locations in Germany to test whether dispensers containing a mixture of farnesene isomers (FIMs) including EBF were able to reduce the infestation of these species on sugar beet. Our results showed a reduction in aphid abundance in the FIM-treated patches in two out of three sites. Therefore, we hypothesize that FIM dispensers could prevent aphid infestation and could be used in combination with other IPM measures. However, more research is required to increase the effect and ensure the reliability of this method.

Synthesis, insecticidal evaluation, crystal structure and theoretical calculations of nine/ten-membered carbon bridged neonicotinoid analogues

Neonicotinoid insecticides acting on the insect nicotinic acetylcholine receptors (nAChRs) played an essential role in contemporary pest control. The development of pesticide resistance due to frequent pesticide use had made it increasingly difficult to control pests. In order to explore neonicotinoid insecticide with low cross-resistance and higher potency, larger carbon bridge compounds were constructed by introducing cyclohexanone and cycloheptene in accordance with our previous research. A series of novel neonicotinoid analogues with nine/ten-membered carbon bridge were designed and synthesized, which exhibited a range of insecticidal activities. The results indicated that some the target compounds showed good insecticidal activities against Bemisia tabaci and Aphis gossypii at 100 ppm. In particular, the activities of compounds A1 and A10 reached 90 % and 97 % respectively, which were similar to that of the control group. Density Functional Theory (DFT) calculations were used to explain the differences in the insecticidal activities of compounds A10, A11, and A12 against Bemisia tabaci. The lowest LUMO energy (ELUMO) of compound A11 (-1.56 eV) might lead to its reduced insecticidal activities. The present study might be meaningful for directing the design of carbon bridged neonicotinoid analogues.

Historical museum samples reveal signals of selection and drift in response to changing insecticide use in an agricultural pest moth.

In response to environmental and human-imposed selective pressures, agroecosystem pests frequently undergo rapid evolution, with some species having a remarkable capacity to rapidly develop pesticide resistance. Temporal sampling of genomic data can comprehensively capture such adaptive changes over time, for example, by elucidating allele frequency shifts in pesticide resistance loci in response to different pesticides. Here, we leveraged museum specimens spanning over a century of collections to generate temporal contrasts between pre- and post-insecticide populations of an agricultural pest moth, Helicoverpa armigera. We used targeted exon sequencing of 254 samples collected across Australia from the pre-1950s (prior to insecticide introduction) to the 1990s, encompassing decades of changing insecticide use. Our sequencing approach focused on genes that are known to be involved in insecticide resistance, environmental sensation, and stress tolerance. We found an overall lack of spatial and temporal population structure change across Australia. In some decades (e.g., 1960s and 1970s), we found a moderate reduction of genetic diversity, implying stochasticity in evolutionary trajectories due to genetic drift. Temporal genome scans showed extensive evidence of selection following insecticide use, although the majority of selected variants were low impact. Finally, alternating trajectories of allele frequency change were suggestive of potential antagonistic pleiotropy. Our results provide new insights into recent evolutionary responses in an agricultural pest and show how temporal contrasts using museum specimens can improve mechanistic understanding of rapid evolution.

Design, synthesis, antimicrobial activity, and mechanism of novel 3-(2,4-dichlorophenyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole derivatives.

Plant pathogens cause substantial crop losses annually, posing a grave threat to global food security. Fungicides have usually been used for their control, but the rapid development of pesticide resistance renders many ineffective, therefore the search for novel and efficient green pesticides to prevent and control plant diseases has become the top priority in crop planting. The results of bioassay studies indicated that most of the target compounds showed certain antimicrobial activity in vitro. In particular, compound X7 showed high inhibitory activity against Xanthomonas oryzae pv. oryzae (Xoo), with an EC50 value of 27.47 μg mL-1, surpassing conventional control agents such as thiazole zinc (41.55 μg mL-1) and thiodiazole copper (53.39 μg mL-1). Further studies on molecular docking showed that X7 had a strong binding affinity with 2FBW. The morphological change observed by scanning electron microscopy indicated that the surface of Xoo appears wrinkled and cracked under X7 treatment and a total of 2662 proteins were identified by label-free proteomic analysis. Three experiments have elucidated the mechanism whereby X7 induced considerable changes in the physiological and biochemical properties of Xoo, which in turn affected the reproduction and growth of bacteria. This work represents a pivotal advancement, offering important reference for the research and development therapeutics in combating plant pathogens. © 2024 Society of Chemical Industry.

Susceptibility of Different Developmental Stages of the Tobacco Cutworm, Spodoptera litura (Fabricius) to Entomopathogenic Nematode, Steinernema abbasi PN-1

The tobacco cutworm, Spodoptera litura Fabricius is a widely distributed polyphagous pest that is causing economic damage to different crop plants. Many pesticides have been used extensively to control S. litura, but they are currently ineffective because of the development of pesticide resistance and their detrimental effects on the environment and human health. Although entomopathogenic nematodes (EPNs) have been employed as biological control agents against S. litura, little is known about the pathogenicity of these EPNs. Here we studied the virulence of Steinernema abbasi PN-1 against different stages of S. litura. The results reveled that all tested larval stages and pupae of S. litura were found susceptible to S. abbasi. There was a positive correlation between insect mortality and the nematode concentration. The S. abbasi caused 100 per cent larval mortality at 48-60 h of post treatment in all tested doses in laboratory. There was a positive correlation between insect mortality and the nematode concentration while the time to cause complete mortality was negatively correlated with the increase in larval days and nematode concentration. However, further field studies are required use S. abbasi as efficient biological control agents against S. litura.

Integrated pest management goes hand-in-hand with safety

This publication is geared toward pest management specialists, certified pesticide applicators, and homeowners who are managing indoor and outdoor pests. It provides a broad definition of a pest and describes integrated pest management (IPM) and pest management strategies. As opposed to other EDIS which are specific to management areas (ex: landscape, turf, vegetable) this publication can be used as a basis for all sectors of pest management. The publication also emphasizes using IPM to reduce the development of pesticide resistance and emphasizes how each aspect of IPM contributes to personal and environmental safety.

Nanomaterial-encapsulated dsRNA of ecdysone-induced early gene E75, a potential RNAi-based SIT strategy for pest control against Bactrocera dorsalis

Bactrocera dorsalis is a notorious pest widely distributed across most Asian countries. With the rapid development of pesticide resistance, new pest control methods are urgently needed. RNAi-based sterile insect technique (SIT) is a species-specific pest management strategy for B. dorsalis control. It is of great significance to identify more target genes from B. dorsalis, and improve the RNAi efficiency. In this study, microinjection-based RNAi results showed that six 20E response genes were necessary for male fertility of B. dorsalis, of which E75 was identified as the key target according to the lowest egg-laying number and hatching rate after E75 knockdown. Three nanoparticles chitosan (CS), chitosan‑sodium tripolyphosphate (CS-TPP), and star polycation (SPc) were used to encapsulate dsE75 expressed by HT115 strain. Properties analysis of nanoparticle-dsRNA complexes showed that both CS-TPP-dsRNA and SPc-dsRNA exhibited better properties (smaller size and polydispersity index) than CS-dsRNA. Moreover, oral administration of CS-TPP-dsE75 and SPc-dsE75 by males resulted in more abnormal testis and significantly lower fertility than feeding naked dsE75. Semi-field trials further confirmed that the number of hatched larvae was dramatically reduced in these two groups. Our study not only provides more valuable targets for RNAi-based SIT, but also promotes the application of environment-friendly management against B. dorsalis in the field.

Individual and Combined Effects of Predatory Bug Engytatus nicotianae and Trichoderma atroviride in Suppressing the Tomato Potato Psyllid Bactericera cockerelli in Greenhouse Grown Tomatoes

The tomato potato psyllid (TPP) Bactericera cockerelli is a serious pest of the Solanaceae family. The management of this pest using synthetic pesticides is problematic because of the development of pesticide resistance and environmental concerns including impacts on non-target organisms. The predatory bug Engytatus nicotianae has recently been identified as a useful biocontrol agent for TPP in greenhouses. The soil fungus Trichoderma Pers. is commonly used as a plant growth enhancer and biocontrol agent against phytopathogenic fungi. Therefore, there could be advantages associated with the combined use of these biocontrol agents. Some reports in other systems suggest that Trichoderma inoculation may alter the behaviour of pests and their natural enemies by modifying plant defence metabolites such as volatile organic compounds (VOCs). For this reason, this study aimed to investigate the individual and combined efficacy of these biocontrol agents (i.e., Trichoderma atroviride and E. nicotianae) against TPP in greenhouse grown tomatoes (Solanum lycopersicum cv. Merlice). To this end, we compared the effect of each biocontrol agent and their combination on TPP abundance across different developmental stages (egg, nymphs, adults) and the number of infested leaves. We also investigated plant VOC emissions under the different treatments. Across all measured TPP stages, the treatments tested (E. nicotianae alone, T. atrovirdae alone, and T. atrovirdae + E. nicotianae) significantly reduced mean TPP counts relative to the control, and no significant differences were observed in VOC emissions among treatments. Overall, T. atrovirdae alone was less effective than E. nicotianae alone and its combination with T. atrovirdae in suppressing TPP populations. However, the combined use of Trichoderma + E. nicotianae did not show significant advantages over the use of E. nicotianae alone in controlling TPP. Therefore, their combined use needs to be further assessed in light of other advantages of Trichoderma to the crop (e.g., growth promotion or pathogen defence).

A chromosome-level genome assembly of Stenchaetothrips biformis and comparative genomic analysis highlights distinct host adaptations among thrips

Insects have a limited host range due to genomic adaptation. Thysanoptera, commonly known as thrips, occupies distinct feeding habitats, but there is a lack of comparative genomic analyses and limited genomic resources available. In this study, the chromosome-level genome of Stenchaetothrips biformis, an oligophagous pest of rice, is assembled using multiple sequencing technologies, including PacBio, Illumina short-reads, and Hi-C technology. A 338.86 Mb genome is obtained, consisting of 1269 contigs with a contig N50 size of 381 kb and a scaffold N50 size of 18.21 Mb. Thereafter, 17,167 protein-coding genes and 36.25% repetitive elements are annotated. Comparative genomic analyses with two other polyphagous thrips, revealing contracted chemosensory-related and expanded stress response and detoxification gene families in S. biformis, potentially facilitating rice adaptation. In the polyphagous thrips species Frankliniella occidentalis and Thrips palmi, expanded gene families are enriched in metabolism of aromatic and anthocyanin-containing compounds, immunity against viruses, and detoxification enzymes. These expansion gene families play crucial roles not only in adapting to hosts but also in development of pesticide resistance, as evidenced by transcriptome results after insecticides treatment. This study provides a chromosome-level genome assembly and lays the foundation for further studies on thrips evolution and pest management.

Sustainable Management for Spiralling Whitefly, Aleurodicus dispersus Russell (Hemiptera: Aleyrodidae) Infesting Guava and Its Effects on the Natural Enemies’ Complex

The spiralling whitefly, Aleurodicus dispersus (Hemiptera: Aleyrodidae), is one of the most notorious insect pests among tropical fruits and vegetables. A common pest management technique is the application of chemical insecticides. However, this has led to environmental degradation, natural enemy reduction, development of pesticide resistance and increased cost of production. This study, therefore, evaluated the efficacy of a sustainable and eco-friendly management strategy against the spiralling whitefly infesting guava (Psidium guajava L). The experiment was carried out with seven treatments replicated five times following the randomized complete block design. The treatments were negative control (T1), 0.8% soybean oil (T2), 1.6% liquid dishwashing (T3), 1.6% neem oil (T4), 0.4% soybean oil + 0.8% liquid dishwashing (T5), 0.8% neem oil + 0.8% liquid dishwashing (T6) and chemical control (Thiamethoxam 25 WG at 2g/L-1) (T7). Results showed that 1.6% liquid dishwashing was superior among treatments against the 1st, 2nd and 3rd nymphal instars with an average mortality of 84.28, 85.22 and 81.81%, respectively. Application of 0.8% soybean oil showed the highest efficacy against the eggs, 4th instar and adult population with an average mortality of 75.50, 81.36 and 93.50%, respectively. Application of these treatments showed no adverse effects on the natural enemies’ complex associated with guava. Integration of other eco-friendly pest management strategies against the invasive spiralling whitefly is recommended for future research.

Pesticide susceptibility monitoring of fall armyworms (Spodoptera frugiperda (J.E. Smith)): a simple methodology for information-sharing among Southeast Asian countries

BackgroundThe fall armyworm, Spodoptera frugiperda, is a destructive moth pest. It is highly migratory and was first detected in Southeast Asia in 2018, rapidly becoming a major pest of corn production in this region. Monitoring the susceptibility of S. frugiperda populations is important for efficient insecticide resistance management. Because of the high mobility of this pest, information-sharing of susceptibility levels among neighboring countries is required for insecticide resistance management. To this end, we developed simple standard methods for pesticide susceptibility monitoring of S. frugiperda to contribute to information-sharing among Southeast Asian countries.MethodsThe developed methods included mass rearing of larvae using an artificial diet and bioassay by diet overlay. The lethal concentrations for 50% and 95% mortality (LC50 and LC95) and resistance coefficient values were calculated. We tested the susceptibilities of samples of S. frugiperda collected from the six major corn planting areas in Thailand to emamectin benzoate, spinetoram, chlorantraniliprole, indoxacarb, chlorfenapyr, and lufenuron using the developed methods.ResultsThe mortality of artificial diet-fed larvae was higher than those fed corn leaves, especially in the early instars. However, more than half of the specimens reared on the artificial diet became pupae. In the case of three of the six pesticides, emamectin benzoate, indoxacarb, and chlorfenapyr, the LC50 values of the samples collected in 2021 and 2022 were significantly higher than those collected in 2019, indicating increasing resistance to those three pesticides. According to the resistance coefficient values, only samples from one area exhibited low resistance to lufenuron.ConclusionsWe developed a simple standardized methodology for Southeast Asian countries to compare insecticide susceptibility. The calculated LC50 and resistance coefficient values can be used as a baseline for monitoring the development of pesticide resistance in the region. The LC50 values of several pesticides have increased significantly over the years. However, the resistance coefficient values indicated that S. frugiperda developed low resistance to only one pesticide (lufenuron). This study offers helpful information for insecticide selection and improved resistance management of fall armyworms in Thailand.

Evaluation of field resistance in field-collected mosquito Culex quinquefasciatus Say through quantification of ULV permethrin/PBO formulation in field bioassays.

Pyrethroids are among the most applied adulticides worldwide to control mosquito vectors for prevention of arboviral diseases transmission. However, pesticide resistance development in a mosquito population could lead to decreased control efficacy. While most studies investigate the resistant genotype (i.e. kdr, CYP450, etc.) as explanatory variables, few field efficacy studies have measured pesticide quantities deposited at different distances from the sprayer in association with observed mosquito mortality. The current study determined field delivered amounts of an applied ULV permethrin/PBO formulation (31% permethrin + 66% piperonyl butoxide) by GC/MS and estimated practical resistance ratios using caged mosquito females. For field samples, the extraction method recovered 78 ± 3.92-108 ± 8.97% of the permethrin/PBO formulation when utilizing the peaks of PBO from GC/MS to estimate the concentrations of adulticide deposited near the mosquito cages. The field bioassay showed that the spatial distribution of permethrin/PBO formulation was heterogeneous among three pseudo-replicates within the same distance. Within the quantifiable permethrin/PBO range of 15.7-51.4 ng/cm2 , field-collected mosquito mortalities started at 64% and linearly increased reaching 100% only in two areas, while all Sebring susceptible mosquitoes died. The field LC95 resistance ratio (RR) of F0 Cx. quinquefasciatus ranged from 2.65-3.51, falling within the 95% CI of RR95 estimated by laboratory vial assays. Tests with and without PBO indicated P450's enzymes contributed to field resistance. Results showed the suitability of the collection and quantification method to estimate the field resistance ratio at the applied pesticide rate. Pesticide quantification would also allow the association of the known frequencies of resistance mechanisms (e.g. kdr, CYP450) with field mortalities to estimate the resistance level conferred by such mechanisms. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Deciphering Plant-Insect-Microorganism Signals for Sustainable Crop Production.

Agricultural crop productivity relies on the application of chemical pesticides to reduce pest and pathogen damage. However, chemical pesticides also pose a range of ecological, environmental and economic penalties. This includes the development of pesticide resistance by insect pests and pathogens, rendering pesticides less effective. Alternative sustainable crop protection tools should therefore be considered. Semiochemicals are signalling molecules produced by organisms, including plants, microbes, and animals, which cause behavioural or developmental changes in receiving organisms. Manipulating semiochemicals could provide a more sustainable approach to the management of insect pests and pathogens across crops. Here, we review the role of semiochemicals in the interaction between plants, insects and microbes, including examples of how they have been applied to agricultural systems. We highlight future research priorities to be considered for semiochemicals to be credible alternatives to the application of chemical pesticides.

Role of ionizing radiation in the management of the Greater Wax Moth (Galleria mellonella L.): a comparative analysis of different types of ionizing radiation

Galleria mellonella L., is an insect pest of the honey bee combs and causes huge economic losses worldwide. Its management heavily relies on the use of chemical pesticides. However, chemical pesticides have drawbacks, including the incidence of colony collapse disorder and the development of pesticide resistance. Ionizing radiation has the potential to treat infested bee combs without leaving chemical footprints, thereby increasing agricultural output in general and honey production in particular. In the current study, research on how the type, energy, and dose rate of ionizing radiation affect radiation-induced damage was done on the eggs and larvae of G. mellonella. It was observed that although larval mortality increases with electron beam energy, egg hatchability depends more on dose rate and less on the energy of gamma and x-ray radiation in the MeV range of energy. Additionally, a significant association between dose rate and larval mortality was seen. Doses of 179.40 Gy and 158.60 Gy, respectively, of 0.66 MeV gamma rays and 15 MeV electrons, were required to stop pupal development completely. Gamma radiation in the MeV range of energy was found to be the most suitable modality of all ionizing radiation.

Control efficacy of azadirachtin on the fall armyworm, Spodoptera frugiperda (J. E. Smith) by soil drenching.

The fall armyworm (FAW), Spodoptera frugiperda, is an important agricultural pest species native to the Western Hemisphere and has recently invaded to Africa and Asia. Owing to the development of pesticide resistance and environmental contamination, ecofriendly pesticides are desirable for FAW control. Azadirachtin is a plant-derived natural pesticide with low toxicity to humans and the natural environment. Azadirachtin is primarily applied by foliar spraying; however, this approach lowers the efficacy of controlling target insects owing to photodegradation and might give a harmful effect on nontarget beneficial insects. Thus, we investigated whether applying azadirachtin to soil improves FAW control and its toxicity to corn plants. Soil drainage of azadirachtin exhibited no phytotoxic effects on corn plants but significantly reduced the larval body weight and delayed the developmental period of each larval instar of FAW. Applying 10, 15, and 20 ppm azadirachtin to soil inhibited larval growth by 68%, 76%, and 91%, respectively. Furthermore, the survival rate of FAW gradually decreased when larvae were fed azadirachtin-treated corn leaves. Collectively, this is the first study suggesting the systemic efficacy of azadirachtin by soil drenching against FAW.

Dynamic Roles of Insect Carboxyl/Cholinesterases in Chemical Adaptation.

Insects have evolved several intricate defense mechanisms to adapt to their chemical environment. Due to their versatile capabilities in hydrolytic biotransformation, insect carboxyl/cholinesterases (CCEs) play vital roles in the development of pesticide resistance, facilitating the adaptation of insects to their host plants, and manipulating insect behaviors through the olfaction system. CCEs confer insecticide resistance through the mechanisms of qualitative or quantitative changes of CCE-mediated enhanced metabolism or target-site insensitivity, and may contribute to the host plant adaptation. CCEs represent the first odorant-degrading enzymes (ODEs) discovered to degrade insect pheromones and plant odors and remain the most promising ODE candidates. Here, we summarize insect CCE classification, currently characterized insect CCE protein structure characteristics, and the dynamic roles of insect CCEs in chemical adaptation.

Effects of Lymantria dispar multiple nucleopolyhedrovirus and Bacillus thuringiensis var. kurstaki on different larval instars of Lymantria dispar asiatica.

Outbreaks of Lymantria dispar asiatica (the Asian spongy moth; Lepidoptera: Erebidae) occur sporadically, causing widespread damage to forest and fruit trees. Owing to the development of pesticide resistance and environmental contamination, biopesticides, including L.dispar multiple nucleopolyhedrovirus(LdMNPV) and Bacillus thuringiensis var. kurstaki (Btk), can significantly contribute to controlling overall larval stage of this species. Although both pathogens are highly effective at the larval stage, their effects on different instar stages have not been investigated. In this study, we analyzed the mortality and lethality in different L. dispar asiatica instars exposed to single or combined pathogen treatments. Treatments with low or medium LdMNPV concentrations induced lower mortality and had higher LT50 values at the 4th and 5th instars compared with other instars, whereas high LdMNPV treatments induced high mortality in all instars, with higher LT50 values at later instars. Treatment with Btk induced a rapid 100% mortality in all instars, with higher LT50 values for the later instars. The combination of LdMNPV and Btk delayed the killing time compared with the effects of single treatments, with the effect being more pronounced in the 1st and 5th instar stage than at other stages at low Btk concentrations. Our findings indicate that the pathogenic effects of LdMNPV and Btk on L. dispar asiatica differ according to larval stage, thereby providing novel insights into enhancing the biological control efficacy of these agents against L. dispar asiatica in the field.

Functional characterization of tyrosine melanin genes in the white-backed planthopper and utilization of a spray-based nanoparticle-wrapped dsRNA technique for pest control

As a significant pest of rice the white-backed planthopper (WBPH) Sogatella furcifera is a focus of pest management. However, traditional chemical-based control methods risk the development of pesticide resistance as well as severe ecological repercussions. Although nanoparticle-encapsulated dsRNAs provide a promising alternative method for sustainable pest management, gene targets specific to WBPH have yet to be optimized. Genes in the tyrosine-melanin pathway impact epidermal melanization and sclerotization, two processes essential for insect development and metabolism, have been proposed as good candidate targets for pest management. Seven genes (aaNAT, black, DDC, ebony, tan, TH, and yellow-y) in this group were identified from WBPH genome and functionally characterized by using RNAi for their impact on WBPH body color, development, and mortality. Knockdown of SfDDC, Sfblack, SfaaNAT, and Sftan caused cuticles to turn black, whereas Sfyellow-y and Sfebony knockdown resulted in yellow coloration. SfTH knockdown resulted in pale-colored bodies and high mortality. Additionally, an Escherichia coli expression system for large-scale dsRNA production was coupled with star polycation nanoparticles to develop a sprayable RNAi method targeting SfTH that induced high WBPH mortality rates on rice seedlings. These findings lay the groundwork for the development of large-scale dsRNA nanoparticle sprays as a WBPH control method.

Can Essential Oils Be a Natural Alternative for the Control of Spodoptera frugiperda? A Review of Toxicity Methods and Their Modes of Action

Spodoptera frugiperda is a major pest of maize crops. The application of synthetic insecticides and the use of Bt maize varieties are the principal strategies used for its control. However, due to the development of pesticide resistance and the negative impact of insecticides on the environment, natural alternatives are constantly being searched for. Accordingly, the objective of this review was to evaluate the use of essential oils (EOs) as natural alternatives for controlling S. frugiperda. This review article covers the composition of EOs, methods used for the evaluation of EO toxicity, EO effects, and their mode of action. Although the EOs of Ocimum basilicum, Piper marginatum, and Lippia alba are the most frequently used, Ageratum conyzoides, P. septuplinervium. O. gratissimum and Siparuna guianensis were shown to be the most effective. As the principal components of these EOs vary, then their mode of action on the pest could be different. The results of our analysis allowed us to evaluate and compare the potential of certain EOs for the control of this insect. In order to obtain comparable results when evaluating the toxicity of EOs on S. frugiperda, it is important that methodological issues are taken into account.