Sogatella Furcifera Research Articles

Threonyl-tRNA synthetase gene, a potential target for RNAi-based control of three rice planthoppers.

RNA interference (RNAi) has potential as a new strategy for pest control. However, the current overemphasis on the control of a single pest increased control costs. The aim of this study was to find a green method of controlling several pests without affecting the natural enemies with a single target gene. One possible RNAi target is the threonyl-tRNA synthetase (ThrRS), which is conserved and plays a significant role in protein biosynthesis. In this study, one threonyl-tRNA synthetase gene (NlthrS) was identified from the brown planthopper (Nilaparvata lugens). Spatio-temporal expression pattern analysis showed that NlthrS was highly expressed in the ovary, late embryogenesis, nymphs and female adults. In addition, RNAi-mediated knockdown of NlthrS caused 85.6% nymph mortality, 100% female infertility, molting disorder, extended nymph duration and shortened adult longevity. Target-specific results were obtained when dsNlthrS was used to interfere with the whiteback planthopper (Sogatella furcifera), small brown planthopper (Laodelphax striatellus), zig-zag winged leafhopper (Inazuma dorsalis) and their natural enemy (green mirid bug, Cyrtorhinus lividipennis). In addition, dsNlthrS could cause high mortalities of three species of planthoppers (85.6-100%), while only dsNlthrS-1 led to the death (97.3%) of I. dorsalis that was not affected by dsNlthrS-2. Furthermore, neither dsNlthrS-1 nor dsNlthrS-2 could influence the survival of C. lividipennis. The results reveal the biological functions of ThrRS in N. lugens in addtion toits protein synthesis, deepening our understanding of tRNA synthase in insects and providing a new method for the control of several rice pests via one dsRNA design. © 2022 Society of Chemical Industry.

Species Composition and DNA Barcoding of Hemipteran Assemblages Throughout Paddy Growing Seasons

Hemipterans are the diverse, abundant, and important pests in the paddy ecosystem due to their piercing and sucking mouthparts that feed on the crop causing significant losses in rice yields. Despite their important roles in the paddy ecosystem, the information on DNA barcode, diversity, and species richness has been occasionally discussed. This study aimed to measure its abundance, species richness, and barcode hemipteran species from the paddy ecosystem. Active sampling was used with two different sampling arrangements in the paddy ecosystem in Sabak Bernam, Selangor, for two different seasons. Hemipterans were collected and identified up to species level morphologically prior to DNA barcoding. The richness and the abundance of species were measured along with the paddy growth phases (vegetative, reproductive, and mature). A total of 2,167 individuals of seven hemipteran species (Cyrtorhinus lividipennis, Leptocorisa oratorius, Nephotettix virescens, Cofana spectra, Sogatella furcifera, Scotinophara coarctata, and Graptostethus sp.) were successfully collected with Shannon-Diversity Index (H’ = 0.4572), Margalef richness index (D = 0.7811), and Evenness Index (E = 0.2257). There was no significant difference (p > 0.05) for species diversity in both seasons. The highest abundance of hemipteran was during the maturity stage (1,543 individuals), followed by the reproductive (591 individuals) and vegetative stages (33 individuals). This study observed a significant difference between the paddy growth for both seasons (p < 0.05). Five hemipteran species namely C. lividipennis, L. oratorius, N. virescens, C. spectra, and S. furcifera, were successfully barcoded with Leptocorisa, the dominant genus. Outcomes from this study suggested that different hemipteran management approaches must be developed to cater to different hemipteran species at different paddy growth stages for a successful and sustainable paddy growing practice in Malaysia.

Molecular Characterization of UDP-N-Acetylglucosamine Pyrophosphorylase and Its Role in the Growth and Development of the White-Backed Planthopper Sogatella furcifera (Hemiptera: Delphacidae).

UDP-N-acetylglucosamine pyrophosphorylase (UAP) is a key enzyme in the chitin biosynthesis pathway of insects. Here, we described the gene SfUAP in the white-backed planthopper Sogatella furcifera (Horváth) with an open reading frame of 1470 bp. Quantitative real-time polymerase chain reaction (qPCR) suggested that SfUAP exhibits a different developmental expression pattern and a higher expression after molting. The highest expression of SfUAP was observed in the integument tissues of adults, whereas head tissues showed negligible expression. RNAi-based gene silencing decreased the mRNA transcript levels in S. furcifera nymphs injected with double-stranded RNA of SfUAP. Finally, SfUAP silencing led to 84% mortality and malformed phenotypes in nymphs. Thus, our results can help better understand the role of SfUAP in S. furcifera.

Sogatella furcifera Saliva Mucin-like Protein Is Required for Feeding and Induces Rice Defences.

The white-backed planthopper (WBPH), Sogatella furcifera, is one of the most important piercing-sucking pests of rice (Oryza sativa) in Asia. Mucin-like salivary protein (SFMLP) is highly expressed in the salivary glands of WBPH, which plays an important role in WBPH feeding. In this study, WBPH injected with dsSFMLP had difficulty in sucking phloem sap from rice plants, which significantly reduced their food intake, weight, and survival. In contrast, the knockdown of the SFMLP gene had only a marginal effect on the survival of WBPH fed an artificial diet. Further studies showed that silencing SFMLP resulted in the short and single-branched salivary sheaths secretion and less formation of salivary flanges in rice. These data suggest that SFMLP is involved in the formation of the salivary sheath and is essential for feeding in WBPH. Overexpression of the SFMLP gene in rice plants promoted the feeding of WBPH, whereas silencing the gene in rice plants significantly decreased WBPH performance. Additionally, it was found that overexpression of SFMLP in rice plants elicited the signalling pathway of SA (salicylic acid) while suppressing JA (jasmonic acid); in contrast, silencing of the SFMLP gene in rice plants showed the opposite results. This study clarified the function of SFMLP in WBPH feeding as well as mediating rice defences.

Discovery of Pyrido[1,2-a]pyrimidine Mesoionic Compounds Containing Benzo[b]thiophene Moiety as Potential Pesticide Candidates.

The increasing evolution of insect resistance has made it challenging for traditional insecticides to control the bean aphid (Aphis craccivora Koch). To address this pending issue, a range of pyrido[1,2-a]pyrimidine mesoionic compounds containing benzo[b]thiophene were designed and synthesized. The biological activity test results of the target compounds indicated that they had moderate to outstanding insecticidal activity against the bean aphid (Aphis craccivora) and moderate insecticidal activity against the white-backed planthopper (Sogatella furcifera). Compound L14 exhibited significant insecticidal activity against A. craccivora, with an LC50 value of 1.82 μg/mL, which was superior to triflumezopyrim (LC50 = 4.76 μg/mL). The results of enzyme activity assay showed that compound L14 had a definite inhibitory effect on ATPase. Moreover, the proteomics and docking findings of compound L14 suggested that it may act on the central nervous system of aphids and interact with nicotinic acetylcholine receptors. Therefore, compound L14 is a potentially novel insecticide candidate for further utilization.

Combined Effects of Soil Silicon and Host Plant Resistance on Planthoppers, Blast and Bacterial Blight in Tropical Rice.

Simple SummaryRice is often attacked by several herbivores and plant pathogens at the same time. Public research has mainly focused on enhancing rice resistance against these biotic stresses by selecting rice lines with resistance genes during breeding programs. However, rice resistance to biotic stresses is also affected by soil nutrients, including available nitrogen and silicon. Nitrogen tends to reduce resistance, but silicon can increase resistance. We assessed the effects of combining soil silicon with host plant resistance against rice planthoppers, blast disease, and bacterial blight disease. We used pure silicon (SiO2) to avoid the confounding effects of nutrients associated with silicates. We also assessed the effects of nitrogenous fertilizer on silicon-augmented resistance to planthoppers. We found that high nitrogen diminishes the capacity of soil silicon and host resistance to reduce planthopper fitness (i.e., nitrogen was antagonistic); but that silicon counters nitrogen-related reductions in rice antixenosis defenses (e.g., repellency) against gravid female planthoppers (i.e., an additive effect of silicon and resistance). Silicon augmented resistance against blast and bacterial blight, but the effects were most apparent on susceptible varieties. Plants infected with bacterial blight generally grew larger in silicon amended soils. We discuss how silicon improves seedling quality by augmenting broad-spectrum resistance.Soil silicon enhances rice defenses against a range of biotic stresses. However, the magnitude of these effects can depend on the nature of the rice variety. We conducted a series of greenhouse experiments to examine the effects of silicon on planthoppers (Nilaparvata lugens [BPH] and Sogatella furcifera [WBPH]), a leafhopper (Nephotettix virescens [GLH]), blast disease (Magnaporthe grisea) and bacterial blight (Xanthomonas oryzae) in susceptible and resistant rice. We added powdered silica gel (SiO2) to paddy soil at equivalent to 0.25, 1.0, and 4.0 t ha−1. Added silicon reduced BPH nymph settling, but the effect was negligible under high nitrogen. In a choice experiment, BPH egg-laying was lower than untreated controls under all silicon treatments regardless of nitrogen or variety, whereas, in a no-choice experiment, silicon reduced egg-laying on the susceptible but not the resistant (BPH32 gene) variety. Stronger effects in choice experiments suggest that silicon mainly enhanced antixenosis defenses. We found no effects of silicon on WBPH or GLH. Silicon reduced blast damage to susceptible and resistant (Piz, Piz-5 and Pi9 genes) rice. Silicon reduced damage from a virulent strain of bacterial blight but had little effect on a less virulent strain in susceptible and resistant (Xa4, Xa7 and Xa4 + Xa7 genes) varieties. When combined with resistance, silicon had an additive effect in reducing biomass losses to plants infested with bacterial blight (resistance up to 50%; silicon 20%). We discuss how silicon-containing soil amendments can be combined with host resistance to reduce biotic stresses in rice.

Intelligent Monitoring System of Migratory Pests Based on Searchlight Trap and Machine Vision.

Three species of rice migratory pests (Cnaphalocrocis medinalis, Sogatella furcifera, and Nilaparvata lugens) cause severe yield and economic losses to rice food every year. It is important that these pests are timely and accurately monitored for controlling them and ensuring food security. Insect radar is effective monitoring equipment for migratory pests flying at high altitude. But insect radar is costly and has not been widely used in fields. Searchlight trap is an economical device, which uses light to trap migratory pests at high altitude. But the trapped pests need to be manually identified and counted from a large number of non-target insects, which is inefficient and labor-intensive. In order to replace manual identification of migratory pests, we develop an intelligent monitoring system of migratory pests based on searchlight trap and machine vision. This system includes a searchlight trap based on machine vision, an automatic identification model of migratory pests, a Web client, and a cloud server. The searchlight trap attracts the high-altitude migratory insects through lights at night and kills them with the infrared heater. All trapped insects are dispersed through a multiple layers of insect conveyor belts and a revolving brush. The machine vision module collects the dispersed insect images and sends them to the cloud server through 4G network. The improved model YOLO-MPNet based on YOLOv4 and SENet channel attention mechanism is proposed to detect three species of migratory pests in the images. The results show that the model effectively improves the detection effect of three migratory pests. The precision is 94.14% for C. medinalis, 85.82% for S. furcifera, and 88.79% for N. lugens. The recall is 91.99% for C. medinalis, 82.47% for S. furcifera, and 85.00% for N. lugens. Compared with some state-of-the-art models (Faster R-CNN, YOLOv3, and YOLOv5), our model shows a low false detection and missing detection rates. The intelligent monitoring system can real-timely and automatically monitor three migratory pests instead of manually pest identification and count, which can reduce the technician workload. The trapped pest images and historical data can be visualized and traced, which provides reliable evidence for forecasting and controlling migratory pests.

Non-Preference Mechanism of Resistance in Rice Germplasm Accessions to Whitebacked Planthopper Sogatella furcifera (Horvath)

Non-Preference Mechanism of Resistance in Rice Germplasm Accessions to Whitebacked Planthopper Sogatella furcifera (Horvath)

Immigration Pathways of White-Backed Planthopper in the Confluence Area of the Two Monsoon Systems.

The white-backed planthopper, WBPH, Sogatella furcifera (Horváth) is a plant pest that migrates long-distances. The migration pathway of WBPH in eastern China coincides with the north-south round trip of the East Asian monsoon. However, in Yunnan China, which is affected by two monsoon systems, the migration pathway is unclear. Light-trap data and analysis of female ovarian development showed that the peak period of immigration of WBPH into western Yunnan was earlier than in eastern Yunnan. Using meteorological reanalysis data and flight parameters of WBPH, trajectory modeling showed that there are two immigration pathways to Yunnan. One is from Myanmar to western Yunnan, and the other is from Vietnam and Laos to eastern Yunnan. The reason for the differences in source areas and immigration pathways between eastern and western Yunnan is that the west wind prevails in western Yunnan and is controlled by South Asian monsoon, while southwesterly winds prevail in eastern Yunnan due to the combined influence of South Asian monsoon and East Asian monsoon. The results indicate that WBPH invades Yunnan via two pathways under a two-monsoon system. These data will allow earlier prediction and population management of WBPH.

CeO2 nanohybrid as a synergist for insecticide resistance management

Agricultural applications of nanomaterials, such as nanofertilizers, nanopreservation technologies, nanopesticides, and plant nanosensors, have recently attracted much attention. Herein, the CeO2-based nanohybrid MON@CeO2 was designed as a reactive oxygen species (ROS) inhibitor to effectively improve the susceptibility of insect pests to insecticides. MON@CeO2 was fabricated by intercalating CeO2 into mesoporous organosilica nanoparticles (MONs). The obtained MON@CeO2 showed a regular spherical shape with an average particle size of 45.4 nm, good monodispersity, and a negative surface charge (-14.6 mV). Bioassay results showed that MON@CeO2 significantly enhanced the toxicity (more than 2-fold) of nitenpyram, sulfoxaflor, and clothianidin against laboratory insecticide-resistant and field strains of Nilaparvata lugens. In particular, MON@CeO2 orchestrated host detoxification metabolism via downregulating ROS-dependent P450 gene expression, thus reducing host detoxification enzyme activities to overcome insecticide resistance. Furthermore, MON@CeO2 restrained host insecticide resistance in the notorious agricultural pests Aphis gossypii, Spodoptera frugiperda, and Sogatella furcifera. Therefore, MON@CeO2 could be used as a broad-spectrum nanosynergist against insecticide resistance, which would be a novel strategy for sustainable pest management.

The Entomopathogenic Fungus Metarhizium anisopliae Affects Feeding Preference of Sogatella furcifera and Its Potential Targets' Identification.

The rice planthopper Sogatella furcifera is a unique vector of the southern rice black-streaked dwarf virus (SRBSDV). The feeding behavior of S. furcifera should directly affect the diffusion of this virus. In this study, we noted that the infection of Metarhizium anisopliae CQMa421 on S. furcifera disturbed the feeding behavior of this pest to SRBSDV-infected rice, from preference to non-preference. Then, we further investigated the potential targets of M. anisopliae CQMa421 on the feeding behavior of S. furcifera after 0 h, 24 h and 48 h of infection by transcriptomic analysis via Illumina deep sequencing. A total of 93.27 GB of data was collected after sequencing, from which 91,125 unigenes were annotated, including 75 newly annotated genes. There were 1380 vs. 2187 and 137 vs. 106 upregulated and downregulated differentially expressed genes (DEGs) detected at 24 h and 48 h, respectively. The biological functions and associated metabolic processes of these genes were determined with the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. The results suggested that major of DEGs are involved in energy metabolism, biosynthesis, immune response, the FoxO signaling pathway, the MAPK signaling pathway and apoptosis in response to the fungal infection. Noteworthily, several olfactory-related genes, including odorant receptors and odorant binding proteins, were screened from these differentially expressed genes, which played critical roles in regulating the olfactory behavior of insects. Taken together, these results provide new insights for understanding the molecular mechanisms underlying fungus and host insect interaction, especially for olfactory behavior regulated by fungus.

Identification of Alien Introgression Lines Resistant to White Backed Planthopper, Sogatella furcifera (Horvath) in Rice

Introgression lines of wide cross derivatives were screened to identify resistant/tolerant entries for WBPH biotypes under artificial condition. The main objective of this study is to provide breeders with more ‘attractive’ plant genetic resources that are easier to use, i.e. resistance sources in acceptable genetic background; or inbreeding tolerant forms disomic lines for inbred or hybrid rice breeding programme. Forty six pre-breeding lines were evaluated against White Backed Plant Hopper (WBPH) under glasshouse condition over a period of two years (2019 and 2020). Out of these, seven pre-breeding lines are moderately resistant to WBPH having score 5. Three pre-breeding lines are moderately susceptible to WBPH having score 7 and rest thirty four pre-breeding lines are highly susceptible to WBPH with a score of 9.

Resistance of Sogatella furcifera to triflumezopyrim mediated with the overexpression of CYPSF01 which was regulated by nuclear receptor USP

Sogatella furcifera is one of the main agricultural pests in many Asian countries, bringing about enormous injury. A triflumezopyrim-resistant (Tri) strain of S. furcifera was established through continuous screening in laboratory. The determination of synergist and enzyme activity indicated that P450s, especially for the upregulation expression of CYPSF01, played a key role in the increased resistance, confirmed by RNAi, and the recombinant protein of CYPSF01 and NADPH-P450 reductase was able to degrade triflumezopyrim. CYPSF01 had an obviously co-expression relationship with nuclear receptor ultraspiracle (USP), which were all significantly up-regulated when exposed to triflumezopyrim. Further, a USP-binding motif MA0534.1 was enriched from the upregulated peaks by Assay for Transposase Accessible Chromatin (ATAC-seq) analysis, which exited in the peaks located on the promoter of CYPSF01; the yeast one-hybrid experiments confirmed that USP could bind to the CYPSF01 promoter. And the USP interference significantly down-regulated CYPSF01 expression, and resulted in the significantly increasing sensitivity to triflumezopyrim, its mortality rate increased 28.37%. Therefore, the overexpression of USP could cause to the overexpression of CYPSF01, ultimately resulting in the resistance to triflumezopyrim in S. furcifera.

Design, Synthesis, and Insecticidal Activity of Novel Pyrido[1, 2-a]pyrimidinone Mesoionic Compounds Containing an Indole Moiety as Potential Acetylcholine Receptor Insecticides.

In this study, a series of novel mesoionic pyrido[1,2-a]pyrimidinone compounds containing a natural skeleton indole were designed and synthesized, and the insecticidal activities of the target compounds were tested. The results showed that the target compounds had good to excellent insecticidal activities against white-backed planthoppers (Sogatella furcifera) and bean aphids (Aphis craccivora). Among them, compound 7 showed outstanding insecticidal activities against both S. furcifera and A. craccivora, with LC50 values of 0.86 and 0.85 μg/mL, respectively. The insecticidal activity against bean aphids (A. craccivora) was superior to that of triflumezopyrim (LC50 = 3.67 μg/mL). Proteomics and quantitative real-time polymerase chain reaction (qRT-PCR) results revealed that compound 7 may interact with α1 and α7 nAChR subunits of S. furcifera. The results of enzyme activities indicated that compound 7 was an inhibitor of AChE in S. furcifera. This study provides new ideas for the discovery of new mesoionic pyrido[1,2-a]pyrimidinone insecticides.

Silencing the Autophagy-Related Genes ATG3 and ATG9 Promotes SRBSDV Propagation and Transmission in Sogatella furcifera.

Simple SummaryPlant viruses are mostly transmitted by insects and cause severe damage to crops. The southern rice black-streaked dwarf virus is a rice virus exclusively transmitted by a planthopper, Sogatella furcifera. Autophagy is usually initiated as an adaptive response for cell survival in unfavorable conditions, such as pathogen invasion. The invasion of the virus in the vector may elicit autophagy and may subsequently function to suppress or promote virus propagation and transmission in the insect vector. Here, we annotated two key autophagy-related genes, SfATG3 and SfATG9, in the planthopper vector and found that the genes are conserved among various insects. Interestingly, exposure of the vector to the virus activated the expression of SfATG3 and SfATG9, and silencing SfATG3 or SfATG9 promoted propagation and transmission rates of the virus. These results indicate that the expression of autophagy-related genes is initiated in the vector following exposure to the virus and that autophagy-related genes functions to suppress SRBSDV propagation and transmission.Autophagy plays diverse roles in the interaction among pathogen, vector, and host. In the plant virus and insect vector system, autophagy can be an antiviral/pro-viral factor to suppress/promote virus propagation and transmission. Here, we report the antiviral role of autophagy-related genes ATG3 and ATG9 in the white-backed planthopper (Sogatella furcifera) during the process of transmitting the southern rice black-streaked dwarf virus (SRBSDV). In this study, we annotated two autophagy-related genes, SfATG3 and SfATG9, from the female S. furcifera transcriptome. The cDNA of SfATG3 and SfATG9 comprised an open reading frame (ORF) of 999 bp and 2295 bp that encodes a protein of 332 and 764 amino acid residues, respectively. SfATG3 has two conserved domains and SfATG9 has one conserved domain. In S. furcifera females exposed to SRBSDV, expression of autophagy-related genes was significantly activated and shared similar temporal patterns to those of SRBSDV S9-1 and S10, all peaking at 4 d post viral exposure. Silencing the expression of SfATG3 and SfATG9 promoted SRBSDV propagation and transmission. This study provides evidence for the first time that S. furcifera autophagy-related genes ATG3 and ATG9 play an antiviral role to suppress SRBSDV propagation and transmission.

Main and Ratooned Rice Pest Populations in Lowland Rice Fields, South Sumatra Applied Bioinsecticide from Entomopathogens

The pests that attack each plant phase also varies. The aimed of this study was to compare the main population of rice insect pests and ratooned in lowland rice field in the vegetative, flowering and milk ripening phase. The main bioinsecticide rice sprayed on rice canopy were comes from the entomopathogenic fungal conidia Metarhizium anisopliae, the entomopathogenic bacterium Bacillus thuringiensis, and as a control area without the application of bioinsecticide or synthetic insecticide. The results showed that population of fake white pests (Cnaphalocrosis medinalis) and white leafhoppers pest (Covana spectra) were more prevalent in vegetative phase rice compared to other types of pests such as green leafhoppers (Nephotettix spp.), Brown leafhoppers (Nilaparvata lugens), zig zag leafhoppers. (Recillia dorsalis), white-back leafhoppers (Sogatella furcifera), grasshoppers, mole cricket (Gryllotalpa gryllotalpa), and yellow rice stem borer (Scirpophaga incertulas). The Leptocorisa acuta and green ladybugs (Nezara viridula) began to attack the flowering and milk ripening phase, which was when the rice was aged about 54-68 days after transplanting (dat). Whereas in ratooned rice, the pest population of L. acuta has appeared on the first observation on rice aged 9 days after harvest (dah) until the ratooned rice was aged 58 days after harvesting. The population of pests was higher in land without bioinsecticide application compared to land applied of bioinsecticides. In ratooned rice, the pest population between the land applied with bioinsecticide M. anisopliae and B. thuringiensis was not significantly different from the land applied by B. thuringiensis which was sold in the market.

Bioefficacy of ethiprole + pymetrozine against the white-backed planthopper Sogatella furcifera (Howard), in rice (ADT – 46)

The nymphs and adults of white-backed planthoppers (Sogatella furcifera, Howard) remove plant sap resulting in yield loss. Indiscriminate use of insecticides, results in the development of resistance by insects and ill effects on the environment opening the new era of chemicals with novel modes of action with good bioefficacy, higher selectivity, low mammalian toxicity and safety to the environment. Therefore, the introduction of newer insecticide molecules with alternate modes of action will play a serious role in pest management programs. Hence, an experiment was conducted to evaluate the bioefficacy of ethiprole + pymetrozine against white-backed planthopper of rice (ADT – 46) under laboratory and field conditions at Annamalai University, Chidambaram during 2018-20. Ethiprole + pymetrozine @ (T1 - 36.91 + 138), (T2 - 40.13 + 150) and (T3 - 45.47 + 170) g a.i ha-1 with standard checks T4 - pymetrozine @ (150) g a.i ha-1, T5 - buprofezin @ (200) g a.i ha-1 and T6 - ethiprole + imidacloprid @ (50 + 50) g a.i ha-1 were evaluated against white-backed planthopper. The standard checks were of positive control i.e., reference insecticides which is in common use The results revealed that T3 recorded the lowest population of white-backed planthopper/hill at 15 day after spraying (1.13 hoppers/hill in August – December 2018 and 1.79 hoppers/hill in August – December 2019 respectively) giving better yield. The population of natural enemies was comparatively lower in all insecticidal treatments than in the control.

Interactions between Rice Resistance to Planthoppers and Honeydew-Related Egg Parasitism under Varying Levels of Nitrogenous Fertilizer.

Simple SummaryPlanthopper outbreaks in rice are associated with excessive fertilizer applications. Public research has focused on developing resistant rice to combat these outbreaks. However, to preserve ecosystem resilience, natural enemy efficacy should be maintained on resistant and susceptible rice. We examined the impact of egg parasitoids on planthoppers (Nilaparvata lugens (Stål) [BPH] and Sogatella furcifera (Horváth) [WBPH]) and a leafhopper (Nephotettix virescens (Distant) [GLH]) in field plots of resistant (IR62) and susceptible (IR64) rice under low and high nitrogen. GLH and WBPH were more abundant in low-nitrogen plots during dry (GLH) and wet (GLH, WBPH) season sampling at an early crop stage. GLH were also more abundant on IR64. Parasitoids killed between 24 and 52% of planthopper eggs during exposures in trap plants. Parasitism by Oligosita and Anagrus wasps was higher on IR64 (BPH eggs) and in high-nitrogen plots (Oligosita spp. on BPH and WBPH eggs; Anagrus spp. on BPH eggs). Parasitism by Anagrus spp. was associated with the presence of honeydew and was highest where honeydew was derived from BPH feeding on IR62; these effects were only observed under high nitrogen. Results suggest that honeydew from IR62 favors parasitoids when plants are most vulnerable (i.e., under high nitrogen), thereby countering nitrogen-induced declines in host resistance.Host plant resistance is the most researched method for the management of planthoppers and leafhoppers in tropical rice. For optimal effects, resistance should be resilient to fertilizer inputs and work in synergy with natural enemies. In field plot experiments, we examined how rice resistance and fertilizer inputs affect mortality of planthopper and leafhopper eggs by hymenopteran parasitoids. We used IR62 as a variety with resistance to Nilaparvata lugens (Stål) [BPH], Sogatella furcifera (Horváth) [WBPH] and Nephotettix virescens (Distant) [GLH], and IR64 as a susceptible control. The herbivores were more abundant during wet season sampling in low-nitrogen plots. During this study, parasitoids killed between 31 and 38% of BPH eggs and 24 and 52% of WBPH eggs during four days of field exposure. Parasitism, mainly due to Oligosita spp., was generally higher in high-nitrogen and IR64 plots. Similar densities of eggs in exposed plants suggest that these trends were mediated by semiochemicals and therefore support the Optimal Defense Hypothesis. Honeydew from BPH on IR62 had more xylem-derived wastes than honeydew on IR64. We applied honeydew from both varieties to sentinel plants. Parasitism by Anagrus spp. was higher on plants of either variety treated with honeydew derived from IR62; however, the effect was only apparent in high-nitrogen plots. Results suggest that Anagrus spp., by responding to honeydew, will counter the nitrogen-induced enhancement of planthopper fitness on resistant rice.

Toxicity of Thiamethoxam 25WG and Sulfoxaflor 21.8SC tTo Rice White Backed Planthopper sogatella furcifera (Horvath)

Baseline toxicity of neonicotinoid insecticides viz., thiamethoxam 25WG and sulfoxaflor 21.8SC was assessed in the field collected populations of the rice white backed planthopper Sogatella furcifera (Horvath). The major rice growing regions of Tamil Nadu when studied revealed that the field populations vary in their susceptibility. Coimbatore and Bhavani populations were more susceptible compared to the Nagapattinam one. Baseline toxicity of thiamethoxam 25WG was relatively high with narrow variation (LC50 - 0.3130 to 1.7882 ppm; LC95 - 1.0993 to 6.3840 ppm); LC50 of sulfoxaflor 21.8SC ranged from 1.3121 to 3.8392 ppm, while the LC95 values were 3.1507 to 5.2754 ppm. The resistance ratios varied among the populations viz., thiamethoxam 25WG (2.5 to 5.6 folds) and sulfoxaflor 21.8SC (1.8 to 2.9 folds). Thus, the population from Nagapattinam exhibited maximum resistance.

Efficacy of Benzpyrimoxan 10SC Against Rice Planthoppers

The efficacy of foliar application of benzpyrimoxan 10SC @ 50, 75, 100, 125 and 150 g a.i./ ha besides the insecticidal checks imidacloprid 17.8SL @ 25 g a.i./ha and buprofezin 25SC @ 187.5 g a.i./ha was evaluated against the brown planthopper (BPH) Nilaparvata lugens (Stal.) and the white backed planthopper (WBPH) Sogatella furcifera (Horvath) on rice during kharif 2017 and 2018 at the Punjab Agricultural University, Ludhiana. Experimental design consisted of random blocks in three replications. Two years data revealed that benzpyrimoxan 10SC @ 100 g a.i./ha is significantly superior against the N. lugens and S. furcifera complex. Benzpyrimoxan 10SC @ 100 g a.i./ha gave significantly higher yield (34.17 q/ ha) than its lower doses but was statistically at par with its higher doses. Non-significant differences in number of spiders/hill among treated plots and untreated check at 10- and 15-DAS indicated the safety of benzpyrimoxan.