Rice Planthoppers Research Articles

Oxidative stress and DNA damage in earthworm (Eisenia fetida) induced by triflumezopyrim exposure

Triflumezopyrim is an excellent pesticide for preventing and controlling rice planthoppers. It is widely used in the production of field rice and mainly through spraying with some inadvertent loss of pesticide to the soil. The future may bring development and utilization of seeds containing triflumezopyrim which will certainly impact earthworms. To evaluate the toxic effects of triflumezopyrim on earthworms, reactive oxygen species (ROS), superoxide dismutase (SOD) and catalase (CAT) activities, malondialdehyde content (MDA), glutathione S-transferase (GST), and DNA oxidative damage (8-hydroxy-2′-deoxyguanosine, 8-OHdG) were measured after 7, 14, 21, and 28 d analyzing the effects of 6 concentrations (0, 0.5, 1, 2.5, 5 and 10 mg/kg) of triflumezopyrim, respectively. ROS content did not change significantly in the early stages but showed a significant dose-effect relationship in the late stages. Antioxidant enzymes were activated in most treatment groups, and catalase activity was the same as that in the control group at 28 d. GST activity showed a trend of increasing first and then decreasing whereas MDA content had no obvious change in trend. 8-OHdG showed significant positive correlation with the concentration of triflumezopyrim at 28 d, indicating that the degree of DNA oxidative damage increased accordingly. The results showed that chronic exposure of triflumezopyrim may cause both oxidative stress and DNA damage in earthworms and alter the activity of antioxidant enzymes.

NADPH Oxidase 5 Is Essential for Molting and Oviposition in a Rice Planthopper Nilaparvata lugens.

Simple SummaryThe brown planthopper, Nilaparvata lugens, a plant phloem-sucking Hemipteran insect, has become the most destructive pest for rice—the major food source for half of the world’s population. Nilaparvata lugens possess robust fecundity, enabling population densities to increase quickly in a favorable environment. Nilaparvata lugens has also been used as a model system for ecological studies and for developing effective pest management. To better understand the regulation mechanisms of insect reproduction and to provide insights to improve pest control, we searched N. lugens genome and transcriptome databases and identified an NADPH oxidase 5 gene, which was specifically expressed in ovaries of female adults and freshly laid eggs in rice leaf sheaths. Although homologous NADPH oxidase 5 genes have been identified in many insect species, their reproductive functions remain unknown. In this work, our findings initially reveal a functional role of the NADPH oxidase 5 gene in molting and oviposition in N. lugens. This novel finding improves our understanding of the reproductive strategies in insects and provides a potential molecular target for effective pest control of the rice planthopper.The brown planthopper Nilaparvata lugens is a typical monophagous insect herbivore that feeds exclusively on rice sap. This insect pest causes serious damage to rice crops throughout East Asian countries. Chemical control remains the first choice for managing N. lugens populations; however, the use of insecticides has given rise to planthopper resurgence and additional environmental risks. Nilaparvata lugens is a model insect of Hemiptera because its whole genome sequence has been elucidated and is susceptible to RNA interference. In this study, our findings revealed that a superoxide-generating gene, NADPH oxidase 5 (Nox5), is essential for molting and oviposition in a Hemipteran insect Nilaparvata lugens. Knockdown of Nox5 transcript levels by RNA interference in 2nd–5th-instar nymphs results in significantly lethal deficits in the molting transitions from nymph–nymph and nymph–adult. Nox5 knockdown leads to a reduction of hydrogen peroxide in female ovaries and failure of oviposition from the insect ovipositor into the rice leaf sheath. Here, we provide in vivo evidence demonstrating that Nox5 is a key enzyme for regulating molting and oviposition in this insect species.

Frizzled 2 Functions in the Regulation of TOR-Mediated Embryonic Development and Fecundity in Cyrtorhinus lividipennis Reuter.

The mirid bug, Cyrtorhinus lividipennis Reuter, is an important predator of rice planthoppers in Asia. In a previous study, C. lividipennis fed on gramineous weeds with brown planthopper (BPH) eggs had reduced development compared to those fed on rice with BPH eggs. In the current study, the concentrations of selected amino acids (AAs) were higher in rice than five gramineous species, which might explain the enhanced growth of C. lividipennis on rice. When C. lividipennis was fed on AA-deprived artificial diets, the Wnt/β-catenin pathway was inhibited. Furthermore, C. lividipennis females silenced for expression of Frizzled 2 (Fz2) showed a significant reduction in the Wnt/β-catenin and target of rapamycin (TOR) pathways. Silencing Fz2 led to decreased expression of the vitellogenin gene (Vg), lower Vg accumulation in oocytes, reduced soluble protein in ovaries and fat bodies, reduced titers of juvenile hormone, prolonged preoviposition periods, and lower predation capacity, body weight, and egg numbers as controlled to controls. Fz2 silencing resulted in undeveloped ovaries and the inhibition of oocyte growth in the ovarioles, resulting in decreased numbers of offspring and reduced hatching rates. The silencing of Fz2 also resulted in aberrant embryos with undeveloped eyespots and organs, suggesting that Fz2 is an essential gene for embryonic development, oogenesis, and egg maturation. In summary, this study established a potential link between Wnt and TOR pathways, which interact synergistically to regulate C. lividipennis reproduction in response to AA signals. These results provide valuable new information that can be applied to large-scale rearing of C. lividipennis predators, which is important for reducing planthopper damage in rice fields.

Effects of a novel mesoionic insecticide, triflumezopyrim, on the feeding behavior of rice planthoppers, Nilaparvata lugens and Sogatella furcifera (Hemiptera: Delphacidae)

The rice planthoppers, Nilaparvata lugens and Sogatella furcifera, are important sap-sucking pests of rice in Asia. The mesoionic insecticide triflumezopyrim was previously shown to be highly effective in controlling both N. lugens and S. furcifera. In this study, electropenetrography (EPG) was used to evaluate the effect of three triflumezopyrim concentrations (LC10, LC50 and LC90) on the feeding behavior of N. lugens and S. furcifera. EPG signals of planthoppes indicated that there were six different waveforms NP, N1, N2, N3, N4, and N5, which corresponded to non-penetration, stylet penetration into epidermis, salivation, extracellular movement of stylet, sap ingestion in phloem, and water ingestion in xylem during feeding. Compared to untreated controls, triflumezopyrim at LC50 and LC90 prolonged the duration of the non-penetration period by 105.3 to 333.7%. The probing frequencies of N. lugens exposed to triflumezopyrim at LC10 and LC50 were significantly increased; however, the probing frequencies of S. furcifera showed a significant decrease when exposed to triflumezopyrim at all concentrations. Triflumezopyrim exposure prolonged the duration of salivation and shortened the duration of extracellular movement. The duration of phloem sap ingestion decreased from 37.2 to 77.7% in the LC50 and LC90 treatments, respectively. Differences in feeding behavior in response to triflumezopyrim and pymetrozine were minimal. In summary, the results show that the LC50 and LC90 concentrations of triflumezopyrim inhibit the feeding activities of N. lugens and S. furcifera mainly by prolonging the duration of non-penetration and by shortening the duration of phloem sap ingestion, which may foster more efficient use of triflumezopyrim in Asia.

Recognition of Common Insect in Field Based on Deep Learning

Traditional insect taxonomy methods have high technical requirements, and the ability of artificial identification of insects is insufficient. In order to solve the problem, this paper proposes a method of common insects recognition in field based on transfer learning. A total of 9 kinds of insects, such as mythimna separata, rice borer, rice plant hopper, mole cricket, mantis, locust, grass fly, ladybug, and ditch beetle are collected for classification and identification, those include the main insect pests and some natural enemies of the main food crops in the field, such as wheat, rice, corn, etc. Then we use the digital image processing technology and the confrontation generation network to expend the insect dataset, and build a model based on transfer learning to transfer the knowledge learned by VGG16, VGG19, InceptionV3, and InceptionV4 on the ImageNet dataset to the insect classification and recognition. Experimental results show that the transfer learning training model has better classification performance and higher convergence speed, and data expansion can help extend sample and avoid overfitting. The highest recognition accuracy is up to 97.39% among models, which adopt the VGG19 convolutional neural network to pretrain the model for transfer learning. This method has the high recognition accuracy, less time consumption, simple and convenient, robustness in particular for the translation and rotation, which provides a reference for the identification and classification method of field insects.

Suppression of Rice Planthopper Populations by the Entomopathogenic Fungus Metarhizium anisopliae without Affecting the Rice Microbiota.

Entomopathogenic fungi can regulate insect populations and function as crucial biological control agents against insect pests, but their impacts on nontarget microorganisms are poorly understood. In this study, we investigated the potential of the fungal strain Metarhizium anisopliae CQMa421 to control rice planthoppers under field conditions and its effects on rice microbiota. This fungus suppressed rice planthoppers during this period, and its control efficiency was more than 60% 7 days after application and did not significantly differ from that of the chemical treatment except in 2019. Both treatments showed a smaller population of rice planthoppers than the controls. After application, M. anisopliae was maintained on rice plants for approximately 14 days, showing a decreasing trend over time. Furthermore, the results showed that the bacterial and fungal richness (operational taxonomic units) and diversity (Shannon index) did not significantly differ between the fungal treatment and the controls after application. The major bacterial taxa of Proteobacteria (including Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Deltaproteobacteria), Actinobacteria, Bacteroidetes, and Cyanobacteria accounted for more than 80% of the bacterial community after fungal application, and the major fungal taxa Ascomycota (including Eurotiomycetes, Dothideomycetes, and Sordariomycetes) and Basidiomycota (including Ustilaginomycetes) represented more than 90% of the fungal community. However, the microbial communities of the rice phyllosphere did not significantly change after entomopathogenic-agent application, indicating that the indigenous microbial communities may adapt to fungal insecticide application. Taken together, the results suggest that this fungal agent has good potential for rice planthopper control with no substantial effects on rice microbial communities.IMPORTANCE Entomopathogenic fungi may be used as crucial biocontrol agents for the control of insect pests, but few effective fungal strains have been reported for the control of the rice planthopper, a major pest of rice. More importantly, the impacts of fungal insecticide application on nontarget microorganisms have not been well evaluated, especially under field conditions. Therefore, in this study, we investigated the effects of the fungal strain M. anisopliae CQMa421 on rice planthopper populations from 2017 to 2019 and evaluated its potential impacts on the microbiota of rice plants after application. The results suggested that this fungal agent has good potential for use in the control of rice planthoppers with no significant effects on rice microbial communities, representing an alternative strategy for the control of rice pests.

Effect of plant spacing on incidence of rice planthoppers in transplanted rice crop

The rice planthoppers (RPHs) are considered as important rice pests in Asia including Pakistan. As phloem-feeders, they can cause severe losses to rice. Besides climate their population abundance is also affected by plant spacing. The optimum plant spacing is among the key agronomic parameters that influence crop growth, performance and yield. The present study to examine the effect of rice plant spacing on incidence of RPHs was conducted during Kharif season of 2018 and 2019 at farmer’s field in the Kallar tract. The study composed of four treatments of rice plant spacing viz. 18 × 18 cm, 23 × 23 cm, 28 × 28 cm and 33 × 33 cm. The experiment was set in a Randomized Complete Block Design (RCBD) with three repeats. The nursery of rice cultivar Super Basmati was transplanted with uniform age of 35 days in all treatments. The data regarding RPHs was recorded 60 DAT till harvesting of crop. Results revealed that plant spacing had significant effect on number of tillers per plant, panicle length, sterility %age, plant height, straw and grain yield. The highest grain yield 6.75 tonns per ha was obtained from 23 × 23 cm plant spacing followed by 6.59, 5.83 and 5.46 tonns per ha from 28 × 28 cm, 33 × 33 cm and 18 × 18 cm plant spacing, respectively. Whereas, on an average RPHs population per plant was maximum (48.81) at minimum plant spacing (18 × 18 cm) and was minimum (3.57) at maximum (33 × 33 cm) plant spacing. The incidence of RPHs started 70 DAT and was very low in the beginning of the cropping season. It increased with the age of the crop and reached to a maximum level of 60 per plant at 110 DAT. On the basis of results 28 × 28 cm rice plant spacing could be recommended in RPHs vulnerable areas having good yield, low resource intensive and compatible with green plant protection measures. In turn this little yield reduction will highly pay in lieu of sustainable rice production and environment protection by reducing excessive and irrational use of pesticides and their cost of application and thus enhancing the biodiversity conservation potential of rice crop agroecosystem.

Identification of egg parasitoids of rice leafhoppers and planthoppers (Hemiptera: Cicadellidae and Delphacidae) of economic importance in Taiwan, part 2: Trichogrammatidae (Hymenoptera)

Lectotype female of Japania andoi (= Paracentrobia ( Brachistella ) bicolor ) (left); lectotype slide of Japania andoi (middle); and Pseudoligosita nephotetticum male (right). Photos by Serguei Vladimirovich Triapitsyn and Junsuke Yamasako. • Trichogrammatidae egg parasitoids of five rice leafhopper and planthopper pests were identified in Taiwan. • Sentinel egg method was used to establish reliable host associations of the egg parasitoids. • Pseudoligosita nephotetticum is shown to be the predominant egg parasitoid of rice leafhoppers and planthoppers. • Pseudoligosita nephotetticum is newly recorded from eggs of zig-zag leafhopper Maiestas dorsalis . Trichogrammatid egg parasitoids (Hymenoptera: Trichogrammatidae) of rice leafhoppers and planthoppers (Hemiptera: Cicadellidae and Delphacidae) known from Taiwan are identified taxonomically and illustrated, and their host associations are determined by rearings using sentinel eggs of the key pest species. The previously published records of such egg parasitoids in Taiwan are critically analyzed in the unfortunate absence of almost any voucher specimens. Pseudoligosita nephotetticum (Mani) is shown to be the most common egg parasitoid of the two leafhopper and three planthopper pests of rice in Taiwan: the zig-zag leafhopper Maiestas dorsalis (Motschulsky) (a new host record), the green rice leafhopper Nephotettix cincticeps (Uhler), and the delphacids Laodelphax striatella (Fallén) (small brown planthopper), Nilaparvata lugens (Stål) (brown planthopper), and Sogatella furcifera (Horváth) (whitebacked planthopper). Paracentrobia ( Brachistella ) andoi (Ishii) syn. nov., originally described from Japan as Japania andoi Ishii, and Paracentrobia ( Brachistella ) garuda Subba Rao syn. nov. from Thailand are synonymized under Paracentrobia ( Brachistella ) bicolor (Girault) from northern Queensland, Australia; Pseudoligosita tachikawai (Yashiro) syn. nov., originally described as Oligosita tachikawai Yashiro from Japan, is synonymized under Pseudoligosita nephotetticum . Lectotypes are designated for Japania andoi and Oligosita shibuyae Ishii.

Comparative analysis of diet-associated responses in two rice planthopper species

BackgroundHost adaptation is the primary determinant of insect diversification. However, knowledge of different host ranges in closely related species remains scarce. The brown planthopper (Nilaparvata lugens, BPH) and the small brown planthopper (Laodelphax striatellus, SBPH) are the most destructive insect pests within the family Delphacidae. These two species differ in their host range (SBPH can well colonize rice and wheat plants, whereas BPH survives on only rice plants), but the underlying mechanism of this difference remains unknown. High-throughput sequencing provides a powerful approach for analyzing the association between changes in gene expression and the physiological responses of insects. Therefore, gut transcriptomes were performed to elucidate the genes associated with host adaptation in planthoppers. The comparative analysis of planthopper responses to different diets will improve our knowledge of host adaptation regarding herbivorous insects.ResultsIn the present study, we analyzed the change in gene expression of SBPHs that were transferred from rice plants to wheat plants over the short term (rSBPH vs tSBPH) or were colonized on wheat plants over the long term (rSBPH vs wSBPH). The results showed that the majority of differentially expressed genes in SBPH showed similar changes in expression for short-term transfer and long-term colonization. Based on a comparative analysis of BPH and SBPH after transfer, the genes associated with sugar transporters and heat-shock proteins showed similar variation. However, most of the genes were differentially regulated between the two species. The detoxification-related genes were upregulated in SBPH after transfer from the rice plants to the wheat plants, but these genes were downregulated in BPH under the same conditions. In contrast, ribosomal-related genes were downregulated in SBPH after transfer, but these genes were upregulated in BPH under the same conditions.ConclusionsThe results of this study provide evidence that host plants played a dominant role in shaping gene expression and that the low fitness of BPH on wheat plants might be determined within 24 h after transfer. This study deepens our understanding of different host ranges for the two planthopper species, which may provide a potential strategy for pest management.

Characterization of protein-protein interactions between rice viruses and vector insects.

Planthoppers are the most notorious rice pests, because they transmit various rice viruses in a persistent-propagative manner. Protein-protein interactions (PPIs) between virus and vector are crucial for virus transmission by vector insects. However, the number of known PPIs for pairs of rice viruses and planthoppers is restricted by low throughput research methods. In this study, we applied DeNovo, a virus-host sequence-based PPI predictor, to predict potential PPIs at a genome-wide scale between three planthoppers and five rice viruses. PPIs were identified at two different confidence thresholds, referred to as low and high modes. The number of PPIs for the five planthopper-virus pairs ranged from 506 to 1985 in the low mode and from 1254 to 4286 in the high mode. After eliminating the "one-too-many" redundant interacting information, the PPIs with unique planthopper proteins were reduced to 343-724 in the low mode and 758-1671 in the high mode. Homologous analysis showed that 11 sets and 31 sets of homologous planthopper proteins were shared by all planthopper-virus interactions in the two modes, indicating that they are potential conserved vector factors essential for transmission of rice viruses. Ten PPIs between small brown planthopper and rice stripe virus (RSV) were verified using glutathione-S-transferase (GST)/His-pull down or co-immunoprecipitation assay. Five of the ten PPIs were proven positive, and three of the five SBPH proteins were confirmed to interact with RSV. The predicted PPIs provide new clues for further studies of the complicated relationship between rice viruses and their vector insects.

Similarities and spatial variations of bacterial and fungal communities in field rice planthopper (Hemiptera: Delphacidae) populations.

Rice planthoppers are notorious plant sap-feeding pests which cause serious damage. While several microbes in rice planthoppers have been broadly characterized, the abundance and diversity of bacteria and fungi in field planthoppers are largely unknown. This study investigated the bacterial and fungal community compositions of Chinese wild rice planthoppers Laodelphax striatellus and Sogatella furcifera using parallel 16S rRNA gene amplicon and internal transcribed space region sequencing. The bacteria varied significantly between the species and were partitioned significantly by sex, tissues and host environments in each species. The majority of bacteria were affiliated with the genera Wolbachia, Cardinium, Rickettsia and Pantoea. The abundance of Wolbachia was negatively correlated with that of Cardinium in both planthopper species. Compared with bacteria, the abundance and diversity of fungi did not differ between sexes but both were enriched in the gut. The bacterial community as a whole showed no significant correlation with the fungal community. The majority of fungi were related to Sarocladium, Alternaria, Malassezia, Aspergillus and Curvularia. A phylogenetic analysis revealed that these fungi were closely related to botanic symbionts or pathogens. Our results provide novel insights into the bacteria and fungi of rice planthoppers.

Functional analysis of ecdysteroid biosynthetic enzymes of the rice planthopper, Nilaparvata lugens

Ecdysteroids, insect steroid hormones, play key roles in regulating insect development and reproduction. Hemipteran insects require ecdysteroids for egg production; however, ecdysteroid synthesis (ecdysteroidogenesis) details have not been elucidated. We identified all known genes encoding ecdysteroidogenic enzymes in Nilaparvata lugens and clarified their necessity during nymphal and ovarian development. We confirmed that N. lugens utilized 20-hydroxyecdysone as an active hormone. Assays using heterologous expression of enzymes in Drosophila S2 cells showed conserved functions of enzymes Neverland, CYP306A2, CYP314A1 and CYP315A1, but not CYP302A1. RNA interference and rescue analysis using 20-hydroxyecdysone demonstrated that most of the genes were necessary for nymphal development. The identified N. lugens enzymes showed conserved functions and pathways for ecdysteroidogenesis. Knockdown of ecdysteroidogenic enzyme genes in newly molted females caused failure of egg production: less vitellogenic and mature eggs in ovaries, fewer laid eggs and embryonic development deficiency of laid eggs. Considering the high expressions of ecdysteroidogenic enzyme genes in adults and ovaries, ecdysteroidogenesis in ovaries was critical for N. lugens ovarian development. Our study presents initial evidence that hemipteran insects require ecdysteroidogenesis for ovarian development.

Uptake and Translocation of Triflumezopyrim in Rice Plants.

A new type of mesoionic insecticide triflumezopyrim is mainly used to control rice planthoppers, leafhoppers, etc. In order to study the uptake and translocation characteristics of this new insecticide in rice (Oryza sativa), a method for the detection of triflumezopyrim in rice, soil, and water was established using liquid-liquid extraction and QuEChERS sample pretreatment combined with liquid chromatography-triple quadrupole tandem mass spectrometry. The distribution of triflumezopyrim in rice was investigated after hydroponic treatment and foliar treatment at the concentrations of 2.5 and 5 mg·L-1 within the ranges of 24, 48, and 72 h. The results showed that triflumezopyrim could be absorbed by roots and form a systematic distribution in rice by hydroponic treatment; meanwhile, it could also be absorbed by leaves and transported to the bottom leaves under foliar treatment, but no triflumezopyrim was detected in the roots. Thus, triflumezopyrim exhibited high acropetal translocation within the rice plant. This study provides an important scientific basis for the development of an application strategy of triflumezopyrim to control planthoppers and leafhoppers as well as for the residue detection method and safety evaluation.

Identification of a novel planthopper resistance gene from wild rice (Oryza rufipogon Griff.)

Rice planthoppers, including brown planthopper (BPH) and white-backed planthopper (WBPH), are the most destructive pests in Asian rice cultivation regions. Planthopper resistance genes that have been mapped and characterized advance our understanding of underlying resistance mechanisms and facilitate the breeding of resistant varieties, thereby contributing to an efficient pest management strategy. In this study, a novel resistance gene Bph38 derived from the wild rice species Oryza rufipogon Griff. was found to confer high resistance to BPH and WBPH. Conventional mapping was performed to identify regions associated with BPH and WBPH resistance, and two mapping efforts led to the same region on chromosome 4 flanked by markers RM16563 and RM16763. Bulked-segregant analysis and next-generation sequencing were performed using the same population to detect the resistance gene. Conventional mapping narrowed the region to a 12.3-Mb segment, and fine mapping using BC1F2 recombinants identified a 79-kb segment flanked by markers YM112 and YM190. Near-isogenic lines (NILs) carrying Bph38 in the 9311 (indica) and BR54 (japonica) genetic backgrounds were developed by crossing and backcrossing with marker-assisted selection. The agronomic traits and BPH and WBPH resistance of the NILs were similar to those of the recurrent parents. Mandatory feeding and host-choice tests revealed that Bph38 showed both antibiotic and antixenotic effects in both insects, with stronger effects in indica-background lines. Further fine mapping and characterization of the major gene may result in map-based cloning of the gene and allow its application in breeding insect-resistant rice varieties.

The control of the brown planthopper by the rice Bph14 gene is affected by nitrogen.

Brown rice planthopper (BPH) is a devastating rice pest in Asia. Bph14 is the first cloned BPH-resistance gene in rice, inducing callose deposition while impeding BPH feeding. Nitrogen application affects plant growth and resistance. However, there is little evidence on the influence of nitrogen on the callose content or regulation of rice BPH resistance. In this study, Luoyou9348 (containing Bph14 and highly resistant to BPH) and Yangliangyou6 (without Bph14 and susceptible to BPH) were planted under varying nitrogen regimes (0 , 90, 180 kg ha-1 ) to determine their effects on the resistance levels of rice to BPH feeding. The experiments involved BPH performance, plant volatile profiling and BPH preferences in laboratory and field experiments. We found that BPH egg hatching rate, total number of eggs laid and BPH preference increased with increasing nitrogen application in both rice varieties. However, the expression of Bph14, callose content and BPH feeding significantly declined with an increase in nitrogen fertilization in Luoyou9348, compared with Yangliangyou6. Also, the emission of volatile terpene compounds increased with increasing nitrogen application, which resulted in an increase in BPH numbers on both varieties. Two-way analysis of variance indicated a significant interaction between rice variety and nitrogen in BPH feeding behavior. Our findings provide an insight for addressing problems involved in the incorporation of insecticidal genes into crop plants. The effects of nitrogen on insecticidal gene expression in rice plant defense are discussed. © 2020 Society of Chemical Industry.

Brown rice planthopper (Nilaparvata lugens Stal) detection based on deep learning

The brown rice planthopper (Nilaparvata lugens Stal) is one of the main pests of rice. The rapid and accurate detection of brown rice planthoppers (BRPH) can help treat rice in time. Due to the small size, large number and complex background of BRPHs, image detection of them is challenging. In this paper, a two-layer detection algorithm based on deep learning technology is proposed to detect them. The algorithm for both layers is the Faster RCNN (regions with CNN features). To effectively utilize the computing resources, different feature extraction networks have been selected for each layer. In addition, the second layer detection network was optimized to improve the final detection performance. The detection results of the two-layer detection algorithm were compared with the detection results of the single-layer detection algorithm. The detection results of the two-layer detection algorithm for detecting different populations and numbers of BRPHs were tested, and the test results were compared with YOLO v3, a deep learning target detection network. The test results show that the detection results of the two-layer detection algorithm were significantly better than those of the single-layer detection algorithm. In the tests for different numbers of BRPHs, the average recall rate of this algorithm was 81.92%, and the average accuracy was 94.64%; meanwhile, the average recall rate of YOLO v3 was 57.12%, and the average accuracy rate was 97.36%. In the experiment with different ages of BRPHs, the average recall rate of the algorithm was 87.67%, and the average accuracy rate was 92.92%. In comparison, for the YOLO v3, the average recall rate was 49.60%, and the average accuracy rate was 96.48%.

Baseline determination, susceptibility monitoring and risk assessment to triflumezopyrim in Nilaparvata lugens (Stål)

Triflumezopyrim, a novel mesoionic chemical insecticide, is promoted as a powerful tool for control of susceptible and resistant hopper species in rice throughout Asia. For a newly commercialized insecticide it is important to establish susceptibility baseline, conduct susceptibility monitoring, and assess the risk of resistance via artificial selection to provide foundational information on designing resistance management strategy. The susceptibility baseline of triflumezopyrim was established for three rice planthopper species, Nilarpavata lugens (Stål), Sogatella furcifera (Horváth) and Laodelphax striatellus (Fallén). The LD50 of triflumezopyrim was 0.026, 0.032 and 0.094 ng/individual for the adults of the susceptible strains of S. furcifera, L. striatellus and N. lugens, respectively, determined by a topical application method. Using a rice stem (seedling) dipping method, the LC50 was determined as 0.042, 0.024 and 0.150 mg/L for the nymphs (3rd instar) of the three hopper species, respectively. In the meanwhile, the LC50 of Pyraxalt™ (triflumezopyrim 10% SC) was 0.064 mg/L for the N. lugens susceptible strain. Furthermore, the susceptibility of triflumezopyrim and other five neonicotinoid insecticides were monitored for N. lugens field populations collected from major rice production areas in China in 2015–2019. All monitored populations were susceptible to triflumezopyrim (0.5 to 3.9-fold resistance ratio), and showed no cross-resistance to the other five neonicotinoids. These results suggested that triflumezopyrim is a good option to control resistant N. lugens. In addition, a field-collected population of N. lugens was artificially selected with triflumezopyrim for 20 generations and resulted in 3.5-fold increase in LC50 from F0 and 6.0-fold increase from that of the susceptible strain. The realized heritability (h2) of resistance was estimated as 0.0451 by using threshold trait analysis. With this h2 value, the projected triflumezopyrim resistance development (a 10-fold increase in LC50) would be expected after 30.3 or 24.0 generations if 80% or 90% of the population was killed at each generation.

Identification of Major Locus Bph35 Resistance to Brown Planthopper in Rice

An introgression line RBPH660, derived from wild rice Oryza rufipogon, showed stable resistance to brown planthopper (BPH). Segregation analysis indicated BPH resistance of RBPH660 was controlled by multiple genes/QTLs. By using the bulked segregant analysis (BSA)-seq method, two genomic regions harboring QTLs resistance to BPH were identified from 1.20 to 16.70 Mb on chromosome 4 and from 10.20 to 12.60 Mb on chromosome 9 in RBPH660, respectively. A major resistance locus, designated as Bph35 accounting for 51.27% of the phenotypic variation with a LOD score of 42.51, was mapped to the candidate region of chromosome 4 between InDel (insertion-deletion) markers PSM16 and R4M13. For fine mapping of Bph35, one simple sequence repeat and three newly developed InDel markers were used to screen the recombinants. Finally, the Bph35 locus was delimited in the region from 6.28 to 6.93 Mb and there were 18 predicted protein-encoding genes with a total of 114 non-synonymous single nucleotide polymorphism (SNP) variant sites between the resistant and susceptible parents. Out of these genes, Os04g0193950, encoding a putative NB-ARC (nucleotide- binding adaptor shared by APAF-1, R proteins and CED-4) and LRR (leucine-rich repeat) domain protein with nine non-synonymous SNP substitutions in its coding sequence regions, might be the candidate gene for Bph35. These findings would facilitate the map-based cloning of the Bph35 gene and development of resistant varieties against BPH in rice.

A novel negative thermotaxis behavior in rice planthoppers is regulated by TRPA1 channel.

In the field, we observed that many white-backed planthoppers (Sogatella furcifera, WBPHs) stayed in the top region of rice plants exposed to direct sunshine. It was known that WBPHs frequently took flight when the ground temperature was about 25 °C, then climbed to and flew in a dense layer corresponding to an air temperature of about 16 °C in the sky. Its migration height was higher than the top of the surface temperature inversion. It is still unclear whether WBPHs prefer warm or cold regions, and therefore we studied the thermal responses of WBPHs and other insects using a simulated system. We found that WBPHs preferred a cold region to a warm one, unexpectedly below their comfort temperature zone. After comparative analysis with other insect species, such as small brown planthoppers, brown planthoppers, Trialeurodes vaporariorum (stinkbugs, a predator of planthoppers) and Bemisia tabaci (whitefly), only three planthoppers showed cold preference behavior. RNA interference experiments revealed that this behavior of WBPHs can be regulated by the transient receptor potential (TRP) channels TRPA1 channel. Furthermore, podocarpic acid, an agonist of TRPA1, weakened the cold preference, whereas A-967079, an antagonist of TRPA1, had the opposite effect. We reported a novel cold preference (negative thermotaxis) in rice planthoppers that was regulated in WBPHs by the TRPA1 channel. Cold preference of rice planthoppers is probably related to its choice behavior of the special migratory temperature layer. Our results expanded a new perspective to develop novel strategies for behavioral manipulation and management of rice planthoppers. © 2020 Society of Chemical Industry.

Ultrabithorax is a key regulator for the dimorphism of wings, a main cause for the outbreak of planthoppers in rice.

Rice planthoppers, the most devastating rice pests, occur in two wing forms: the short-wing form for rapid population growth and long-wing form for long-distance migration, which together create the mechanism for outbreak. Here we show that Ultrabithorax (Ubx) is a key regulator for switching between the long- and short-wing forms of rice planthoppers. Ubx is expressed in both forewing and hindwing pads, which is different from the canonical model of Ubx expression. In brown planthoppers, expression of Ubx (NlUbx) is regulated by nutritional status of the rice host. High-quality young plants induce NlUbx expression leading to the short-wing form; low-quality ripe plants reduce NlUbx expression resulting in long-wing form. We also showed that NlUbx is regulated by the insulin receptors NlInR1 and NlInR2. The default expression of NlInR1 inhibits NlUbx resulting in long-wings, while high-quality hosts induce NlInR2 expression, which represses NlInR1 thus promoting NlUbx expression to produce short-wings.