Brown Planthopper Research Articles

Interaction of Predatory Ladybird Beetle, Micraspis discolor with Nilaparvata lugens throughout Paddy Growing Seasons

Coccinellidae is a high-interest family that has performed well and is widely distributed. It is valuable in economic service because it acts as an agricultural biological control agent. The Micraspis discolor (Syn=Verania) (Coleoptera: Coccinellidae) is a successful omnivorous predator in rice ecosystem and functions well as a general biological control for maintaining the population of brown planthopper (BPH) (Nilaparvata lugens), the major rice pest worldwide. Studies of natural enemies’ abundance are necessary to increase the practical use of biological control in agriculture. This study investigated the abundance correlation of M. discolor (prey) and rice pest N. lugens (prey) from two different geographical areas of rice fields in west and south Peninsular Malaysia. The cyclone lightrap and sweep net method succeeded in collecting 185 individuals of M. discolor and N. lugens. The study indicated that M. discolor, and the N. lugens collected from Selangor were more numerous than Johor in the ripening phase than in the reproductive and vegetative phases. M. discolor can be found in all stages of rice growth. There are positive correlations between M. discolor and N. lugens in both localities throughout the rice growing season. The positive correlation highlighted that the number of pests has increased parallel to the number of predators and vice versa. The use of M. discolor as a predator is essential in agriculture, along with the treatment of a healthy ecosystem landscape of diverse vegetation combinations, which helps to reduce the use of pesticides.

The Increase of Insect Pest Population in Paddy Field Managed with an Ecological Approach using Refugia Plants and Biopesticides

Insect pests can damage plants and act as vectors of diseases such as brown planthoppers which can transmit dwarf virus disease. The presence of insect pests is influenced by the type of variety, planting patterns, and excessive use of chemical pesticides so that insect pests increase and are difficult to control. This research wanted to provide insights into the effectiveness of combining insectary plants and biopesticides as ecological strategies to manage paddy (Oryza sativa Linnaeus) insect pests. The study was conducted in February-April 2024 in Sukodadi Village, Sukodadi District, Lamongan Regency. Method of study was conducted using a combination of direct observation, insect traps, and quantitative analysis to evaluate the impact of refugia plants and biopesticides on insect pest populations in paddy fields. The analysis includes the species diversity index (Shannon-Winner), species evenness index, species richness index (Margalef), dominance index (Simpson) and similarity index (Bray-Curtis). The study obtained 2,687 individual insect pests in paddy fields with refugia and fobio and 1,761 individuals in paddy fields without refugia and fobio. Insect pests were more abundant in paddy fields with refugia and fobio compared to fields without refugia and fobio. Refugia provides alternative habitats and additional resources for insect pests, and the use of biopesticides can create temporary ecosystem imbalances, and increase the population of insect pest.

A key ABA biosynthetic gene OsNCED3 is a positive regulator in resistance to Nilaparvata lugens in Oryza sativa.

The gene encoding 9-cis-epoxycarotenoid dioxygenase 3 (NCED3) functions in abscisic acid (ABA) biosynthesis, plant growth and development, and tolerance to adverse temperatures, drought and saline conditions. In this study, three rice lines were used to explore the function of OsNCED3, these included an OsNCED3-overexpressing line (OsNCED3-OE), a knockdown line (osnced3-RNAi) and wild-type rice (WT). These rice lines were infested with the brown plant hopper (BPH; Nilaparvata lugens) and examined for physiological and biochemical changes, hormone content, and defense gene expression. The results showed that OsNCED3 activated rice defense mechanisms, which led to an increased defense enzyme activity of superoxide dismutase, peroxidase, and polyphenol oxidase. The overexpression of OsNCED3 decreased the number of planthoppers and reduced oviposition and BPH hatching rates. Furthermore, the overexpression of OsNCED3 increased the concentrations of jasmonic acid, jasmonyl-isoleucine and ABA relative to WT rice and the osnced3-RNAi line. These results indicate that OsNCED3 improved the stress tolerance in rice and support a role for both jasmonates and ABA as defense compounds in the rice-BPH interaction.

Variations in the relative abundance of hemipteran species in different seasons and stages of rice growth depending on weather variations

Rompin has played an active role in Malaysia's rice production for several decades. However, it also faces a threat, particularly from the hemipteran insect pests. There is limited documentation on the abundance of these insects and their relationship with climatic factors. Therefore, this study aimed to determine the abundance of hemipterans in different growth stages and to understand the effects of climatic factors on their population in rice fields. The study was conducted in farmers' rice fields in Rompin, Pahang, Malaysia, during the main and off-season rice planting. Sweep nets, yellow sticky traps, and yellow pan traps were utilized in each plot. Trapped insects were identified based on the rice planting seasons and growth stages. The trends of climatic factors such as rainfall, temperature, light intensity, and wind speed were analysed and correlated with insect abundance. A total of 23,023 individuals belonging to eight families and eleven species of the hemipteran order were recorded. Nine of these species were pests, namely Leptocorisa oratorius, Recilia dorsalis, Nephotettix virescens, N. nigropictus, Amaurochrous dubius, Nilaparvata lugens, Sogatella furcifera, Nezara viridula, and Scotinophara coarctata. The remaining two species were predators, Cyrtorhinus lividipennis and Polytoxus fuscoviftatus. R. dorsalis, N. lugens, S. furcifera, and A. dubius were found in significantly higher numbers and exceptionally high during rice's late vegetative and early reproductive stages. The maximum temperature significantly increased during the main season, while wind speed increased dramatically during the off-season. Wind speed significantly correlated with N. virescens, S. furcifera, L. oratorius, and A. dubius. On the other hand, rainfall exhibited a significant correlation with L. oratorius. Various pest species and their high populations in this study pose a significant threat to plants due to their preferences for different plant parts and strata.

Transcriptome-wide N6-methyladenosine profiling reveals growth-defense trade-offs in the response of rice to brown planthopper (Nilaparvata lugens) infestation.

N6-Methyladenosine (m6A) is a common messenger RNA (mRNA) modification that affects various physiological processes in stress responses. However, the role of m6A modifications in plants responses to herbivore stress remains unclear. Here, we found that an infestation of brown planthopper (Nilaparvata lugens) female adults enhanced the resistance of rice to N. lugens. The m6A methylome analysis of N. lugens-infested and uninfested rice samples was performed to explore the interaction between rice and N. lugens. The m6A methylation mainly occurred in genes that were actively expressed in rice following N. lugens infestation, while an analysis of the whole-genomic mRNA distribution of m6A showed that N. lugens infestation caused an overall decrease in the number of m6A methylation sites across the chromosomes. The m6A methylation of genes involved in the m6A modification machinery and several defense-related phytohormones (jasmonic acid and salicylic acid) pathways was increased in N. lugens-infested rice compared to that in uninfested rice. In contrast, m6A modification levels of growth-related phytohormone (auxin and gibberellin) biosynthesis-related genes were significantly attenuated during N. lugens infestation, accompanied by the down-regulated expression of these transcripts, indicating that rice growth was restricted during N. lugens attack to rapidly optimize resource allocation for plant defense. Integrative analysis of the differential patterns of m6A methylation and the corresponding transcripts showed a positive correlation between m6A methylation and transcriptional regulation. The m6A modification is an important strategy for regulating the expression of genes involved in rice defense and growth during rice-N. lugens interactions. These findings provide new ideas for formulating strategies to control herbivorous pests. © 2024 Society of Chemical Industry.

Evaluating the MDCK cell permeability of greenly synthesize bimetallic Ag/Zn Nanoparticles using leaf extract of Vallaris solanacea as a potential antipesticide-resistant agent.

Bimetallic nanoparticles, particularly Ag/Zn bimetallic nanoparticles, have gained increasing attention due to their unique properties, making them suitable for a variety of applications such as catalysis, water treatment, and environmental remediation. This study aimed to elucidate the use of bimetallic nanoparticles of Ag/Zn as an alternative to resistant pesticides for pest control. Furthermore, this research demonstrates that BNPs can target specific pollutants and degrade them through various mechanisms. BNP docking with the Nilaparvata lugens cytochrome P450 (CYP6ER1) protein exhibited the lowest binding energy of-7.5 kcal/mol. The cell permeability analysis of BNP in plant cells reveals that the BNP has 0 % permeability towards any cell at-10 kcal/mol energy, which is the lowest free energy translocation pathway. The harmful leftover residues of the pesticides have a higher chance of degradability in case of interaction with BNP validated by chemical-chemical interaction analysis. Additionally, MDCK permeability coefficient of small molecules based on the regression model was calculated for BNP which authenticated the efficiency of BNP. Moreover, Swiss ADMET simulated absorption using a boiled egg model with no blood-brain barrier and gastrointestinal crossing for the expected BNP molecule has been observed. Significantly, the findings indicate that employing bimetallic nanoparticles like Ag/Zn is a crucial strategy for bioremediation because they proficiently decompose pesticides while posing no risk to humans. Our results will facilitate the design of novel BNPs materials for environmental remediation and pest control ensuring human health safety that are predicated on bimetallic nanoparticles.

Field bio-efficacy of some selected combination insecticides against brown plant hopper and gundhi bug in rice

Field bio-efficacy of some selected combination insecticides against brown plant hopper and gundhi bug in rice

Transfection of entomopathogenic Metarhizium species with a mycovirus confers hypervirulence against two lepidopteran pests

Although most known viruses infecting fungi pathogenic to higher eukaryotes are asymptomatic or reduce the virulence of their host fungi, those that confer hypervirulence to entomopathogenic fungus still need to be explored. Here, we identified and studied a novel mycovirus in Metarhizium flavoviride, isolated from small brown planthopper (Laodelphax striatellus). Based on molecular analysis, we tentatively designated the mycovirus as Metarhizium flavoviride partitivirus 1 (MfPV1), a species in genus Gammapartitivirus, family Partitiviridae. MfPV1 has two double-stranded RNAs as its genome, 1,775 and 1,575 bp in size respectively, encapsidated in isometric particles. When we transfected commercial strains of Metarhizium anisopliae and Metarhizium pingshaense with MfPV1, conidiation was significantly enhanced (t test; P-value < 0. 01), and the significantly higher mortality rates of the larvae of diamondback moth (Plutella xylostella) and fall armyworm (Spodoptera frugiperda), two important lepidopteran pests were found in virus-transfected strains (ANOVA; P-value < 0.05). Transcriptomic analysis showed that transcript levels of pathogenesis-related genes in MfPV1-infected M. anisopliae were obviously altered, suggesting increased production of metarhizium adhesin-like protein, hydrolyzed protein, and destruxin synthetase. Further studies are required to elucidate the mechanism whereby MfPV1 enhances the expression of pathogenesis-related genes and virulence of Metarhizium to lepidopteran pests. This study presents experimental evidence that the transfection of other entomopathogenic fungal species with a mycovirus can confer significant hypervirulence and provides a good example that mycoviruses could be used as a synergistic agent to enhance the biocontrol activity of entomopathogenic fungi.

Brown planthoppers manipulate rice sugar transporters to benefit their own feeding

The feeding of piercing-sucking insect herbivores often elicits changes in their host plants that benefit the insect.1 In addition to thwarting a host's defense responses, these phloem-feeding insects may manipulate source-sink signaling so as to increase resources consumed.2,3 To date, the molecular mechanisms underlying herbivore-induced resource reallocation remain less investigated. Brown planthopper (BPH), an important rice pest, feeds on the phloem and oviposits into leaf sheaths. BPH herbivory increases sugar accumulations 5-fold in the phloem sap of leaf sheaths and concurrently induces the expression of two clade III SWEET genes, SWEET13 and SWEET14, in leaf tissues, but not in leaf sheaths of attacked rice plants. Mutations of both genes by genome editing attenuate resistance to BPH without alterations of known chemical and physical defense responses. Moreover, BPH-elicited sugar levels in the phloem sap were significantly reduced in sweet13/14 mutants, which is likely to attenuate BPH feeding behavior on sweet13/14 mutants. In one of the two field seasons tested, the sweet13/14 mutants showed comparable yield to wild types, and in the other season, the mutants demonstrated stronger BPH resistance. These preliminary results suggested that the mutations in these SWEET transporters could enhance BPH resistance without yield penalties. Given that sweet13/14 mutants also exhibit resistance to bacterial blight pathogen, Xanthomonas oryzae pv. oryzae, these SWEET genes could serve as excellent molecular targets for the breeding of resistant rice cultivars.

Design, Synthesis and Bioactivities of Novel Pyridyl Containing Pyrazole Oxime Ether Derivatives.

In this research, with an aim to develop novel pyrazole oxime ether derivatives possessing potential biological activity, thirty-two pyrazole oxime ethers, including a substituted pyridine ring, have been synthesized and structurally identified through 1H NMR, 13C NMR, and HRMS. Bioassay data indicated that most of these compounds owned strong insecticidal properties against Mythimna separata, Tetranychus cinnabarinus, Plutella xylostella, and Aphis medicaginis at a dosage of 500 μg/mL, and some title compounds were active towards Nilaparvata lugens at 500 μg/mL. Furthermore, some of the designed compounds had potent insecticidal effects against M. separata, T. cinnabarinus, or A. medicaginis at 100 μg/mL, with the mortalities of compounds 8a, 8c, 8d, 8e, 8f, 8g, 8o, 8s, 8v, 8x, and 8z against A. medicaginis, in particular, all reaching 100%. Even when the dosage was lowered to 20 μg/mL, compound 8s also expressed 50% insecticidal activity against M. separata, and compounds 8a, 8e, 8f, 8o, 8v, and 8x displayed more than 60% inhibition rates against A. medicaginis. The current results provided a significant basis for the rational design of biologically active pyrazole oxime ethers in future.

Effects of azoxystrobin and difenoconazole on the development, fecundity, and predatory capacity of Cyrtorhinus lividipennis

AbstractThe predatory bug Cyrtorhinus lividipennis Reuter (Hemiptera: Miridae) is an important biological control agent for planthoppers, such as Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), and leafhoppers in rice fields (Oryza sativa L., Poaceae). In this study, the sublethal effects of azoxystrobin and difenoconazole, two fungicides extensively used in rice production, on this predatory bug were investigated. The results indicated that exposure to the two fungicides at the third instar had no influence on developmental duration, but difenoconazole resulted in a 25.2% decrease in the lifespan of adult males. When exposed as newly emerged adults, azoxystrobin caused a 33.5% decrease in female longevity. The pre‐oviposition period of azoxystrobin‐treated females mating with azoxystrobin‐treated males was shortened by 44.9%, compared with the control, whereas the pre‐oviposition period of difenoconazole‐treated females mating with control males was lengthened by 32.2% compared with the control group. However, the two fungicides had no effect on fecundity and egg hatchability. Furthermore, the two fungicides did not impact the average consumption of C. lividipennis of N. lugens individuals. They did stimulate the response of C. lividipennis males to rice plants infested by N. lugens in a two‐choice H‐shaped olfactometer test. Also, the predatory capacity of C. lividipennis males was increased after exposure to difenoconazole, whereas the predatory capacity of females was decreased after exposure to the two fungicides. Overall, our results indicated that azoxystrobin and difenoconazole pose no notable risk to C. lividipennis. These findings establish a foundation for the rational and coordinated utilization of fungicides and biological control agents in rice ecosystems.

Complete genome sequence and genetic characterization of a novel segmented RNA virus infecting Nilaparvata lugens.

The brown planthopper (BPH), Nilaparvata lugens, is a significant agricultural pest capable of long-distance migration and transmission of viruses that cause severe disease in rice. In this study, we identified a novel segmented RNA virus in a BPH, and this virus exhibited a close relationship to members of a recently discovered virus lineage known as "quenyaviruses" within the viral kingdom Orthornavirae. This newly identified virus was named "Nilaparvata lugens quenyavirus 1" (NLQV1). NLQV1 consists of five positive-sense, single-stranded RNAs, with each segment containing a single open reading frame (ORF). The genomic characteristics and phylogenetic analysis support the classification of NLQV1 as a novel quenyavirus. Notably, all of the genome segments of NLRV contained the 5'-terminal sequence AUCUG. The characteristic virus-derived small interfering RNA (vsiRNA) profile of NLQV1 suggests that the antiviral RNAi pathway of the host BPH was activated in response to virus infection. These findings represent the first documented report of quenyaviruses in planthoppers, contributing to our understanding of quenyaviruses and expanding our knowledge of insect-specific viruses in planthoppers.

Integration of molecular breeding and multi-resistance screening for developing a promising restorer line Guihui5501 with heavy grain, good grain quality, and endurance to biotic and abiotic stresses.

Rice, a critical staple on a global scale, faces escalating challenges in yield preservation due to the rising prevalence of abiotic and biotic stressors, exacerbated by frequent climatic fluctuations in recent years. Moreover, the scorching climate prevalent in the rice-growing regions of South China poses obstacles to the cultivation of good-quality, heavy-grain varieties. Addressing this dilemma requires the development of resilient varieties capable of withstanding multiple stress factors. To achieve this objective, our study employed the broad-spectrum blast-resistant line Digu, the brown planthopper (BPH)-resistant line ASD7, and the heavy-grain backbone restorer lines Fuhui838 (FH838) and Shuhui527 (SH527) as parental materials for hybridization and multiple crossings. The incorporation of molecular markers facilitated the rapid pyramiding of six target genes (Pi5, Pita, Pid2, Pid3, Bph2, and Wxb ). Through a comprehensive evaluation encompassing blast resistance, BPH resistance, cold tolerance, grain appearance, and quality, alongside agronomic trait selection, a promising restorer line, Guihui5501 (GH5501), was successfully developed. It demonstrated broad-spectrum resistance to blast, exhibiting a resistance frequency of 77.33% against 75 artificially inoculated isolates, moderate resistance to BPH (3.78 grade), strong cold tolerance during the seedling stage (1.80 grade), and characteristics of heavy grains (1,000-grain weight reaching 35.64 g) with good grain quality. The primary rice quality parameters for GH5501, with the exception of alkali spreading value, either met or exceeded the second-grade national standard for premium edible rice varieties, signifying a significant advancement in the production of good-quality heavy-grain varieties in the southern rice-growing regions. Utilizing GH5501, a hybrid combination named Nayou5501, characterized by high yield, good quality, and resistance to multiple stresses, was bred and received approval as a rice variety in Guangxi in 2021. Furthermore, genomic analysis with gene chips revealed that GH5501 possessed an additional 20 exceptional alleles, such as NRT1.1B for efficient nitrogen utilization, SKC1 for salt tolerance, and STV11 for resistance to rice stripe virus. Consequently, the restorer line GH5501 could serve as a valuable resource for the subsequent breeding of high-yielding, good-quality, and stress-tolerant hybrid rice varieties.

RNAi-mediated knockdown of papilin gene affects the egg hatching in Nilaparvata lugens.

The brown planthopper (BPH), Nilaparvata lugens, is one of the most destructive pests of rice. Owing to the rapid adaptation of BPH to many pesticides and resistant varieties, identifying putative gene targets for developing RNA interference (RNAi)-based pest management strategies has received much attention for this pest. The glucoprotein papilin is the most abundant component in the basement membranes of many organisms, and its function is closely linked to development. In this study, we identified a papilin homologous gene in BPH (NlPpn). Quantitative Real-time PCR analysis showed that the transcript of NlPpn was highly accumulated in the egg stage. RNAi of NlPpn in newly emerged BPH females caused nonhatching phenotypes of their eggs, which may be a consequence of the maldevelopment of their embryos. Moreover, the transcriptomic analysis identified 583 differentially expressed genes between eggs from the dsGFP- and dsNlPpn-treated insects. Among them, the 'structural constituent of cuticle' cluster ranked first among the top 15 enriched GO terms. Consistently, ultrastructural analysis unveiled that dsNlPpn-treated eggs displayed a discrete and distorted serosal endocuticle lamellar structure. Furthermore, the hatchability of BPH eggs was also successfully reduced by the topical application of NlPpn-dsRNA-layered double hydroxide nanosheets onto the adults. Our findings demonstrate that NlPpn is essential to maintaining the regular structure of the serosal cuticle and the embryonic development in BPH, indicating NlPpn could be a potential target for pest control during the egg stage. © 2024 Society of Chemical Industry.

Cross-Resistance to Imidacloprid in Brown Planthopper &lt;i&gt;Nilaparvata lugens&lt;/i&gt; (Stal)

Cross-resistance pattern of imidacloprid resistance in brown planthopper, Nilaparvata lugens (Stål) to three insecticides viz., dinotefuran, pymetrozine and triflumezopyrim was evaluated with laboratory developed imidacloprid resistant (IMI-R) and susceptible populations (IMI-S). IMI-R population had a 6-fold resistance compared to IMI-S population. The LC50 values for dinotefuran in IMI-R and IMI-S populations were 466.6 and 129.2 mg/ L with a resistance ratio of 3.6-fold. Whereas, LC50 values for triflumezopyrim and pymetrozine in IMI-R and IMI-S populations were 0.27 and 0.17 mg/L; 49.07 and 31.5 mg/L with resistant ratios of 1.58 and 1.55, respectively. These findings clearly demonstrated cross-resistance between imidacloprid and dinotefuran but no obvious cross-resistance to triflumezopyrim and pymetrozine.

Heterosis for Interactions between Insect Herbivores and 3-Line Hybrid Rice under Low and High Soil Nitrogen Conditions.

Hybrid rice results from crossing a male-sterile line (the A line) with a pollen doner (the restorer or R line). In 3-line hybrid breeding systems, a fertile B line is also required to maintain A line populations. Heterosis is defined as a condition of traits whereby the hybrid exceeds the average of the parental lines. Heterobeltiosis is where the hybrid exceeds both parents. Hybrid rice may display heterosis/heterobeltiosis for growth, yield and resistance to herbivores, among other traits. In a greenhouse experiment, we assessed the frequency of heterosis for resistance to the brown planthopper (Nilaparvata lugans (BPH)), whitebacked planthopper (Sogatella furcifera (WBPH)) and yellow stemborer (Scirpophaga incertulas (YSB)) in eight hybrids under varying soil nitrogen conditions. We also assessed plant biomass losses due to herbivore feeding as an approximation of tolerance (the plant's capacity to compensate for damage). Nitrogen reduced resistance to all three herbivores but was also associated with tolerance to WBPH and YSB based on improved plant survival, growth and/or yields. Plant biomass losses per unit weight of WBPH also declined under high nitrogen conditions for a number of hybrids, and there were several cases of overcompensation in rice for attacks by this herbivore. There was one case of nitrogen-related tolerance to BPH (increased grain yield) for a hybrid line with relatively high resistance, likely due to quantitative traits. Heterosis and heterobeltiosis were not essential to produce relatively high herbivore resistance or tolerance across hybrids.

Exploring the Resistance of Pigmented Rice to Brown Planthopper (Nilaparvata lugens Stål) by Phenotypic and Genotypic Analyses

Developing new pigmented rice varieties that meet consumers' preferences requires addressing resistance to brown planthopper (BPH), a highly destructive insect pest of rice. To effectively manage this pest, it is essential to explore BPH resistance genes from rice germplasms and incorporate them into elite varieties. The objective of this study was to identify the source of resistance among local and improved pigmented rice varieties in Indonesia against field BPH. Furthermore, the study aimed to characterize their genetic diversity using molecular markers associated with Bph genes and functional markers for these genes. Eighty-eight local varieties from the Indonesian Agricultural Gene Bank, collected across 18 provinces between 1971 and 2019, and four improved varieties, were evaluated using the standard seed box screening test method. Among these entries, 6 local accessions and 1 improved variety exhibited moderate resistance. Genetic analysis of these entries and three randomly selected susceptible entries using 12 SSR and InDel markers associated with Bph gene loci showed that the moderately resistant entries had higher allele numbers (11 to 13) compared to the susceptible entries (4 to 7). These markers could distinguish the resistant group from the susceptible ones in cluster analysis. Genotyping using functional markers further showed that the moderately resistant entries had 2 to 4 combinations of Bph genes. In contrast, the susceptible entries contained neither Bph genes nor only one gene. Local accessions with a 2 to 4 Bph gene combination can be donors of BPH resistance in improving pigmented rice varieties.

Gamma irradiation induced thermotolerance in Metarhizium spp. enhancing biocontrol of Nilapavarta lugens (Stål)

The Brown Planthopper (BPH), Nilaparvata lugens (Stål), is a devastating pest to rice crops in Southeast Asia, primarily due to its resistance to insecticides. As a result, the fungus Metarhizium spp. is used as an alternative control for BPH. However, their efficiency is limited due to delayed infectivity and sensitivity to environmental variables. In this study, two isolates of Metarhizium spp. MLUBN038 and MNMHN031, were induced for thermotolerance and biocontrol potential against Nilapavarta lugens (Stål). A multilocus phylogeny of four protein-coding genes including Beta-tubulin, rpb1, rpb2, and tef has identified the two isolates to be Metarhizium koreanum. Seventy-nine potential thermotolerant mutants were screened from the two isolates. These mutant isolates demonstrated significant tolerance to vegetative heat at 39 °C and enhanced resistance to wet heat stress at 45 °C after exposure for 60 h, outperforming the wild-type (WT) isolates. The mutant isolates also showed increased mycelial growth, conidial germination, and spore production compared to the WT isolates. Two mutant isolates, ML038_Mt 71 and MN031_Mt 46, exhibited the highest efficacy against BPH nymphs (4th-5th instars), resulting in a maximum mortality of 88.82 % and 83.55 %, respectively, compared to the WT (54.07 % and 47.54 %) after 14 days of inoculation in the greenhouse. These two highly virulent mutant isolates presented the lowest LT50 values of 2.88 and 3.72 days at a concentration of 1 × 109 conidia/mL. RAPD analysis revealed genetic diversity between the mutant and WT isolates, indicating distinct diversity profiles and supporting the successful generation of mutant variants. These findings suggest that the use of gamma irradiation and heat stress to induce mutations is crucial for the successful production of thermotolerant mutant isolates. Our results suggest that ML031_Mt 71 and MN031_Mt 46 have potential as effective biocontrol agents.

Effects of imidacloprid combined with validamycin on the population fitness and symbiotic of Nilaparvata lugens (Hemiptera: Delphacidae)

Using a high-efficiency insecticide in combination with fungicides that have different mechanisms of action is a conventional method in the current management of brown planthopper (BPH) resistance. In this study, we investigate the separate and combined effects of the low-toxicity fungicide validamycin and the non-cross-resistant insecticide imidacloprid on the fitness and symbiosis of BPH. These research results indicate that when the proportion of active ingredients in validamycin is combined with imidacloprid at a ratio of 1:30, the toxicity ratio and co-toxicity coefficient are 1.34 and 691.73, respectively, suggesting that the combination has a synergistic effect on the control of BPH. The number of yeast-like symbiotic (YLS) and dominant symbiotic (Noda) in the imidacloprid + validamycin groups were significantly lower than the other three treatment groups (validamycin, imidacloprid, and water). The results of the study on population fitness show that the lifespan of the BPH population in validamycin, imidacloprid, and imidacloprid + validamycin was shortened. Notably, the BPH populations in the imidacloprid + validamycin groups were significantly lower than other groups in terms of average generation cycle, intrinsic growth rate, net reproduction rate, finite rate of increase, and fitness. The Real-time quantitative PCR showed that validamycin and imidacloprid + validamycin can significantly inhibit the expression of the farnesyl diphosphate farnesyl transferase gene (EC2.5.1.21) and uricase gene (EC1.7.3.3), with imidacloprid + validamycin demonstrating the most pronounced inhibitory effect. Our research results can provide insights and approaches for delaying resistance and integrated management of BPH.

Potency and Target Surface Interaction of Diazinoyl Nicotinic Insecticides.

Structure-activity relationships of diazinoyl nicotinic insecticides (diazinoyl isomers and 5- or 6-substituted pyrazin-2-oyl analogues) are considered in terms of affinity to the insect nicotinic acetylcholine receptor (nAChR) and insecticidal activity against the imidacloprid-resistant brown planthopper. Among the test compounds, 3-(6-chloropyridin-3-ylmethyl)-2-(pyrazinoyl)iminothiazoline shows the highest potency in nAChR affinity and insecticidal activity. Aplysia californica acetylcholine binding protein (AChBP) mutants (Y55W + Q57R and Y55W + Q57T) are utilized to compare molecular recognition of nicotinic insecticides with diverse pharmacophores. N-nitro- or N-cyanoimine imidacloprid or acetamiprid, respectively, exhibits a high affinity to these AChBP mutants at a similar potency level. Intriguingly, the pyrazin-2-oyl analogue has a higher affinity to AChBP Y55W + Q57R than that to Y55W + Q57T, thereby indicating that pyrazine nitrogen atoms contact Arg57 guanidinium and Trp55 indole NH. Furthermore, nicotine prefers AChBP Y55W + Q57T over Y55W + Q57R, conceivably suggesting that the protonated nicotine is repulsed by Arg57 guanidinium, consistent with its inferior potency to insect nAChR.