Alanine metabolism mediates energy allocation of the brown planthopper to adapt to resistant rice.

INTRODUCTION: During the adaptation to host plant resistance, herbivorous insects faced the challenge of overcoming plant defenses while ensuring their own development and reproductive success. To achieve this, a strategic allocation of energy resources for detoxification and ecological fitness maintenance became essential. OBJECTIVE: This study aimed to elucidate the intricate energy allocation mechanisms involved in herbivore adaptation that are currently poorly understood. METHODS: The rice Oryza sativa and its monophagous pest, the brown planthopper (BPH), Nilaparvata lugens were used as a model system. An integrated analysis of metabolomes and transcriptomes from different BPH populations were conducted to identify the biomarkers. RNA interference of key genes and exogenous injection of key metabolites were performed to validate the function of biomarkers. RESULTS: We found that alanine was one of the key biomarkers of BPH adaptation to resistant rice variety IR36. We also found that alanine flow determined the adaptation of BPH to IR36 rice. The alanine aminotransferase (ALT)-mediated alanine transfer to pyruvate was necessary and sufficient for the adaptation. This pathway may be conserved, at least to some extent, in BPH adaptation to multiple rice cultivars with different resistance genes. More importantly, ALT-mediated alanine metabolism is the foundation of downstream energy resource allocation for the adaptation. The adapted BPH population exhibited a significantly higher level of energy reserves in the fat body and ovary when fed with IR36 rice, compared to the unadapted population. This rendered the elevated detoxification in the adapted BPH and their ecological fitness recovery. CONCLUSION: Overall, our findings demonstrated the crucial role of ALT-mediated alanine metabolism in energy allocation during the adaptation to resistant rice in BPH. This will provide novel knowledge regarding the co-evolutionary mechanisms between herbivores and their host plants.

Insecticide resistance reduces the profitability of insect-resistant rice cultivars.

INTRODUCTION: Preventing crop yield loss caused by pests is critical for global agricultural production. Agricultural pest control has largely relied on chemical pesticides. The interaction between insecticide resistance and the adaptation of herbivorous pests to host plants may represent an emerging threat to future food security. OBJECTIVES: This study aims to unveil genetic evidence for the reduction in the profitability of resistant cultivars derived from insecticide resistance in target pest insects. METHODS: An experimental evolution system encompassing resistant rice and its major monophagous pest, the brown planthopper Nilaparvata lugens, was constructed. Whole genome resequencing and selective sweep analysis were utilized to identify the candidate gene loci related to the adaptation. RNA interference and induced expression assay were conducted to validate the function of the candidate loci. RESULTS: We found that the imidacloprid-resistant population of N. lugens rapidly adapted to resistant rice IR36. Gene loci related to imidacloprid resistance may contribute to this phenomenon. Multiple alleles in the nicotinic acetylcholine receptor (nAChR)-7-like and P450 CYP4C61 were significantly correlated with changes in virulence to IR36 rice and insecticide resistance of N. lugens. One avirulent/susceptible genotype and two virulent/resistant genotypes could be inferred from the corresponding alleles. Importantly, we found that the virulent/resistant genotypes already exist in the wild in China, exhibiting increasing frequencies along with insecticide usage. We validated the relevance of these genotypes and the virulence to three more resistant rice cultivars. Knockdown of the above two genes in N. lugens significantly decreased both the resistance to imidacloprid and the virulence towards resistant rice. CONCLUSION: Our findings provide direct genetic evidence to the eco-evolutionary consequence of insecticide resistance, and suggest an urgent need for the implementation of predictably sustainable pest management.

Osa-miR162a Enhances the Resistance to the Brown Planthopper via α-Linolenic Acid Metabolism in Rice (Oryza sativa).

The brown planthopper (BPH) is the most serious pest causing yield losses in rice. MicroRNAs (miRNAs) are emerging as key modulators of plant-pest interactions. In the study, we found that osa-miR162a is induced in response to BPH attack in the seedling stage and tunes rice resistance to the BPH via the α-linolenic acid metabolism pathway as indicated by gas chromatography/liquid chromatography-mass spectrometry analysis. Overexpression of osa-miR162a inhibited the development and growth of the BPH and simultaneously reduced the release of 3-hexenal and 3-hexen-1-ol to block host recognition in the BPH. Moreover, knockdown of OsDCL1, which is targeted by osa-miR162a, inhibited α-linolenic acid metabolism to enhance the resistance to the BPH, which was similar to that in miR162a-overexpressing plants. Our study revealed a novel defense mechanism mediated by plant miRNAs developed during the long-term evolution of plant-host interaction, provided new ideas for the identification of rice resistance resources, and promoted a better understanding of pest control.

Poaceae-specific ß-1,3;1,4-d-glucans link jasmonate signalling to OsLecRK1-mediated defence response during rice-brown planthopper interactions.

Brown planthopper (BPH, Nilaparvata lugens), a highly destructive insect pest, poses a serious threat to rice (Oryza sativa) production worldwide. Jasmonates are key phytohormones that regulate plant defences against BPH; however, the molecular link between jasmonates and BPH responses in rice remains largely unknown. Here, we discovered a Poaceae-specific metabolite, mixed-linkage ß-1,3;1,4-d-glucan (MLG), which contributes to jasmonate-mediated BPH resistance. MLG levels in rice significantly increased upon BPH attack. Overexpressing OsCslF6, which encodes a glucan synthase that catalyses MLG biosynthesis, significantly enhanced BPH resistance and cell wall thickness in vascular bundles, whereas knockout of OsCslF6 reduced BPH resistance and vascular wall thickness. OsMYC2, a master transcription factor of jasmonate signalling, directly controlled the upregulation of OsCslF6 in response to BPH feeding. The AT-rich domain of the OsCslF6 promoter varies in rice varieties from different locations and natural variants in this domain were associated with BPH resistance. MLG-derived oligosaccharides bound to the plasma membrane-anchored LECTIN RECEPTOR KINASE1 OsLecRK1 and modulated its activity. Thus, our findings suggest that the OsMYC2-OsCslF6 module regulates pest resistance by modulating MLG production to enhance vascular wall thickness and OsLecRK1-mediated defence signalling during rice-BPH interactions.

Nicotine-mediated dopamine regulates short neuropeptide F to inhibit brown planthopper feeding behavior in tobacco-rice rotation cropping.

BACKGROUND: The tobacco-rice rotation cropping (TRRC) is an ecologically friendly system that can both alleviate soil nicotine pollution and decrease the brown planthopper (BPH, Nilaparvata lugens Stål) fitness on rice. However, few studies on this green and effective rotational cropping system have been reported. In particular, the underlying mechanisms of TRRC on the significant reduction of field pest population at the molecular level is still unknown. RESULTS: Field investigation showed that BPH population decreased significantly in TRRC than in rice-rice successive cropping (RRSC) field. In addition, the short neuropeptide F (NlsNPF) and its receptor NlA7 of BPH had half-times lower levels in the TRRC field. Behavioral bioassay indicated a 1.93-fold increase in the number of salivary flanges of the dsNlsNPF group, while BPH fitness parameters, such as honeydew, weight gain, and mortality decreased significantly. Dopamine (DA) content in BPH decreased by ~11.1% under the influence of nicotine, and its presence increased the expression levels of NlsNPF and NlA7. Exogenous DA application eliminated the inhibitory effects of nicotine on BPH feeding and restored the fitness levels of its parameters. Independent application of either a mixture of dsNlsNPF with a nanocarrier or nicotine to the normal rice field revealed that the latter could produce better effects in combination with dsRNA. CONCLUSION: These findings confirmed that DA regulated NlsNPF to inhibit the BPH feeding behavior in TRRC. The results not only provided novel findings on the mechanism of pest-host interactions, but also presented new method for integrated pest management. © 2023 Society of Chemical Industry.

Population density modulates insect progenitive plasticity through the regulation of dopamine biosynthesis.

Insect fecundity is a quantitative phenotype strongly affected by genotypes and the environment. However, interactions between genotypes and environmental factors in modulating insect fecundity remain largely unknown. This study investigated the impact of population density on the fecundity of Nilaparvata lugens (brown planthopper; BPH) carrying homozygous high- (HFG) or low- (LFG) fecundity homozygous genotypes. Under low population densities, the fecundity and population growth rate of both genotypes showed similar increasing trends across generations, while the trends between HFG and LFG under high population densities were opposite. Through a combination of temporal analysis and weighted gene co-expression network analyses on RNA-seq data of HFG and LFG under low and high population densities in the 1st, 3rd, and 5th generations, we identified 2 gene modules that were associated with these density-dependent progenitive phenotypes. Four pathways related to the neural system were simultaneously enriched by the 2 gene modules. Furthermore, Nlpale, which encodes a tyrosine hydroxylase, was identified as a key gene. The RNA interference of this gene and manipulation of its downstream product dopamine significantly affected the basic and density-dependent progenitive phenotypes of BPH. These findings indicated that dopamine biosynthesis is the key regulatory factor that determines fecundity in response to density changes in different BPH genotypes. Thus, this study provides insights into the interaction of a typical environmental factor and insect genotype during the process of population regulation.

Salivary protein 7 of the brown planthopper functions as an effector for mediating tricin metabolism in rice plants.

The brown planthopper (BPH), Nilaparvata lugens, is an important pest that affects rice (Oryza sativa) production in Asia. The flavone tricin (5,7,4'-trihydroxy-3',5'-dimethoxy flavone) is a valuable secondary metabolite commonly found in rice plants that can defend rice plants against infestation by BPH. BPH damage can reduce the metabolic level of tricin in rice. Our preliminary transcriptome research results showed that BPH salivary protein 7 (NlSP7), is highly responsive to tricin stimuli. However, the function of NlSP7 in mediating the interaction between the rice plant and the BPH is unknown. In this study, we cloned the NlSP7 gene in N. lugens and found that its mRNA level was greater in the presence of high tricin content than low tricin content, regardless of whether the BPHs were fed a rice plant diet or an artificial diet containing 100 mg/L tricin. Knocking down NlSP7 resulted in BPH individuals spending more time in the non-penetration and pathway phase, and less time feeding on the phloem of rice plants. These changes decreased BPH food intake, feeding behavior, and fitness, as well as the tricin content of the rice plants. These findings demonstrate that the salivary protein 7 of BPH functions as an effector for tricin metabolism in rice.

Peroxiredoxin alleviates the fitness costs of imidacloprid resistance in an insect pest of rice.

Chemical insecticides have been heavily employed as the most effective measure for control of agricultural and medical pests, but evolution of resistance by pests threatens the sustainability of this approach. Resistance-conferring mutations sometimes impose fitness costs, which may drive subsequent evolution of compensatory modifier mutations alleviating the costs of resistance. However, how modifier mutations evolve and function to overcome the fitness cost of resistance still remains unknown. Here we show that overexpression of P450s not only confers imidacloprid resistance in the brown planthopper, Nilaparvata lugens, the most voracious pest of rice, but also leads to elevated production of reactive oxygen species (ROS) through metabolism of imidacloprid and host plant compounds. The inevitable production of ROS incurs a fitness cost to the pest, which drives the increase or fixation of the compensatory modifier allele T65549 within the promoter region of N. lugens peroxiredoxin (NlPrx) in the pest populations. T65549 allele in turn upregulates the expression of NlPrx and thus increases resistant individuals' ability to clear the cost-incurring ROS of any source. The frequent involvement of P450s in insecticide resistance and their capacity to produce ROS while metabolizing their substrates suggest that peroxiredoxin or other ROS-scavenging genes may be among the common modifier genes for alleviating the fitness cost of insecticide resistance.

A distinct strain of Arsenophonus symbiont decreases insecticide resistance in its insect host.

Symbiotic bacteria are important drivers of phenotypic diversity in insects. One of the widespread symbionts to have emerged belongs to the genus Arsenophonus, however, its biological functions in most host insects remain entirely unknown. Here we report two distinct Arsenophonus strains in the brown planthopper (BPH), Nilaparvata lugens, a major pest insect in Asian countries that causes significant economic damage through rice crop destruction. Genomic resequencing data suggested that one Arsenophonus strain (S-type) negatively affected the insecticide resistance of the host. Indeed, replacement of the resident Arsenophonus with the S-type Arsenophonus significantly decreased host insecticide resistance. Transcriptome and metabolome analysis revealed down-regulation of xenobiotic metabolism and increased amino acid accumulation in the S-type Arsenophonus infected host. This study demonstrates how a symbiont-mediated phenotypic change can occur. The results of this study will aid in developing strategies that work through imposing an ecological disadvantage on insect pests, which will be of great value for pest control in agricultural industry.

Molecular identification of spiders preying on Empoasca vitis in a tea plantation.

Biological control using predators of key pest species is an attractive option in integrated pest management (IPM). Molecular gut analysis can provide an estimation of predator efficiency on a given prey. Here we use a combination of various experimental approaches, both in field and lab, to identify a potential biological control species of the common pest of commercially grown tea, Empoasca vitis (Göthe) (Hemiptera), in a Chinese plantation. We collected 2655 spiders from plantations and established relative abundances of spider species and their temporal overlap with the pest species in tea canopy. We analyzed DNA from 1363 individuals of the most common spider species using targeted RQ-PCR to quantify the potential efficiency of spiders as a predator on E. vitis. The results showed that, in the field, the jumping spider Evarcha albaria was the most abundant, had the closest temporal overlap with the pest, and frequently fed on it. Therefore, this spider may play a key role in pest suppression. The present study demonstrates the potential of our experimental approach to study predator-prey relationships in taxa that do not lend themselves to morphological identification of gut contents, such as spiders.

Main predators of insect pests: screening and evaluation through comprehensive indices.

BACKGROUND: Predatory natural enemies play key functional roles in integrated pest management. However, the screening and evaluation of the main predators of insect pests has seldom been reported in the field. Here, we employed comprehensive indices for evaluating the predation of a common pest (Ectropis obliqua) by nine common spider species in Chinese tea plantations. RESULTS: We established the relative dominance of the spider species and their phenological overlap with the pest species, and analyzed DNA from the nine spider species using targeted real-time quantitative polymerase chain reaction to identify the residual DNA of E. obliqua. The predation rates and predation numbers per predator were estimated by the positive rates of target fragments and the residual minimum number of E. obliqua in predators' guts, respectively. The results showed that only four spider species preyed on E. obliqua, and the order of potential of the spiders to control E. obliqua from greatest to smallest was Neoscona mellotteei, Xysticus ephippiatus, Evarcha albaria and Coleosoma octomaculatum by the Z-score method. CONCLUSION: The orb-weaving spider N. mellotteei has the maximum potential as a biological control agent of E. obliqua in an integrated pest management strategy. An approach of screening and evaluating main predators of insect pests through comprehensive indices was preliminarily established. © 2017 Society of Chemical Industry.