Brown Planthopper Management Research Articles

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.

Effect of silicon application on rice plant defence against brown planthopper feeding under climate change conditions

Abstract Silicon (Si) is known to enhance plant resistance in rice and other Poaceae plants by priming chemical defence, physiological, and mechanical barriers. However, the effects of application of Si to the soil on plant defence through antioxidative enzymes and changes in the nutrient composition of soil and rice straw under climate change conditions remain unclear. Thus this study was aimed at investigating the effects of Si on plant defence and other biochemical changes in the brown planthopper (BPH), Nilaparvata lugens (Stål, 1854), soil and rice plants under elevated CO2 levels (570 ± 25 ppm) and elevated temperature (≃3°C higher than ambient) in open-top chambers (OTCs) during the rainy season of 2019 and 2020. The results revealed that under elevated CO2, Si amendment significantly enhanced the activity of defensive antioxidative enzymes, namely catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) upon BPH feeding in both plants and BPH, besides enhancing available forms of major nutrients, namely nitrogen (N), phosphorus (P), potassium (K), and minor nutrients, namely calcium (Ca), magnesium (Mg) and sulphur (S), and Si in soil and rice plants. The antioxidative enzymes’ mediated plant defence and positive alteration of the nutrient composition of soil along with other reported plant defences, namely callose deposition, silicification, and positive alteration of photosynthesis-related parameters, indicated Si amendment as a potential alternative strategy for BPH management under climate change conditions.

Molecular analysis of NlugCSP3 with behaviorally active ligands of the brown planthopper, Nilaparvata lugens (Hemiptera: Delphacidae)

The insect olfactory system is sensitive to the complicated chemical environment. Insect’s chemosensory proteins (CSPs) supposedly act as transport of plant volatiles across the sensillar lymph and competitive fluorescent binding assay was commonly used to test the binding affinities with various plant volatiles. However, extensive research to determine the physiological role of CSPs is necessary and helpful through binding interaction of a protein with the plant volatiles. In this comparative study, we employed phylogenetic analysis, fluorescence spectra, quenching mode, and thermodynamic force to characterize Nilaparvata lugens CSP3 (NlugCSP3). The phylogenetic tree revealed that amino acid sequence of NlugCSP3 showed extremely close similarities with Laodelphax striatella (LstrCSP10 & LstrCSP11) and Sogatella furcifera (SurCSP3). The Stern-Volmer (SV) curve of NlugCSP3 fluorescence quenching indicated that nonadecane and 2-tridecanone clearly quenched NlugCSP3 fluorescence as a stable static quenching mode. Meanwhile, α-terpinene and farnesene collided with NlugCSP3, instead of forming stable complexes. The thermodynamic analysis of NlugCSP3 revealed that spontaneous binding interaction occurred in nonadecane and 2-tridecanone and is driven primarily by hydrophobic interactions. This study not only provides the information about the binding interaction of protein with the volatiles, but also improves the efficient recognition of behaviorally elicited volatiles that could be used in the management of brown planthopper.

Integrated Pest Management of Brown Plant Hopper (Nilaparvata lugens (Stal)) in rice of Mancherial District, Telangana State, India

The present study on Integrated Pest Management (IPM) of brown plant hopper, Nilaparvata lugens (Stal) in rice has been conducted as a Front Line Demonstration (FLD) in the adopted villages of KVK, Bellampalli, Mancherial district of Telangana state during the kharif (June – December), season of 2018‒19, 2019‒20 and 2020‒21 respectively to create awareness among the farming community on the IPM practices to manage the pest. The adoption of IPM practices includes formation of alleyways, recommended dose of nitrogen fertilizer, alternate wetting and drying, spraying of need based insecticides like Dinotefuran 20 SG @ 0.4 g or Pymetrozine 50 WDG @ 0.6 g l-1 of water were carried out. The study reveals that the lowest hoppers incidence was witnessed in the demonstrated plot with 1.84, 12.18 and 19.0 adults hill-1 in tillering stage and 7.76, 24.95 and 52.38 adults hill-1 in panicle stage over farmers practice (3.33, 35.40 and 25.42 adults hill-1 in tillering stage and 19.84, 50.30 and 63.47 adults hill-1). The average yields of IPM module demonstrated plot was 7130, 5513 and 5065 kg ha-1 whereas in farmer practice the yield was 6733, 4851 and 4768 kg ha-1 during Kharif (June–December), 2018‒19, 2019‒20 and 2020‒21 respectively with an increased yield of 5.88%, 13.64% and 6.22% during corresponding Kharif (June–December), 2018‒19, 2019‒20 and 2020‒21. Further the Cost-Benefit ratio of 1.88, 2.68 and 1.78 in the technology demonstrated plots whereas in farmers practice the recorded Cost-Benefit ratio of 1.43, 1.94 and 1.48 during corresponding Kharif (June–December), 2018‒19, 2019‒20 and 2020‒21 respectively.

Transcriptome and metabolome analyses reveal the responses of brown planthoppers to RH resistant rice cultivar.

The brown planthopper (BPH) Nilaparvata lugens (Stål) (Hemiptera: Delphacidae) is one of the most destructive rice pests in Asia. The application of insect-resistant rice cultivars is currently one of the principal means of controlling BPH. Understanding the physiological response mechanisms of BPH feeding on insect-resistant rice is the key for maintaining rice yield. Here, we measured the ecological fitness and analyzed the whole-body transcriptome and metabolome of BPH reared on susceptible cultivar Taichung Native 1 (TN1) and resistant cultivar Rathu Heenati (RH). Our results showed that RH significantly decreased the survival rate, female adult weight, honeydew secretion, the number of eggs laid per female and fat content of BPH. We identified 333 upregulated and 486 downregulated genes in BPH feeding on RH. These genes were mainly involved in energy metabolism, amino acid metabolism, hormone synthesis and vitamin metabolism pathways. We also detected 145 differentially accumulated metabolites in BPH reared on RH plants compared to BPH reared on TN1 plants, including multiple carbohydrates, amino acids, lipids, and some nucleosides. Combined analyses of transcriptome and metabolome showed that five pathways, including starch, sucrose, and galactose metabolism, were altered. The network for these pathways was subsequently visualized. Our results provide insights into the mechanisms of metabolite accumulation in BPH feeding on the RH rice variety. The results could help us better understand how insect-resistant rice cultivars combat BPH infestation, which is important for the comprehensive management of BPH.

Evaluation of pesticide combinations against brown planthopper and sheath blight in rice

Field experiment was conducted at Regional Agricultural Research Station, Maruteru, West Godavari (A.P.) during two kharif seasons of 2019 and 2020 to evaluate the compatibility of combinations of insecticides and fungicides against brown planthopper and sheath blight in rice. The results revealed that pymetrozine and triflumezopyrim as sole treatments are highly effective against brown planthopper (BPH), Nilaparvata lugens (Stal) by registering over 90% reduction in BPH population. While, pymetrozine and triflumezopyrim in combination with azoxystrobin and azoxystrobin + tebuconazole are highly effective against BPH and sheath blight, Rhizoctonia soloni Kuhn in by registering over 90% and >50% reduction in BPH population and sheath blight severity, respectively and registered 64.23% to 73.03% higher grain yields than untreated control. It was also found that there was no adverse effect of fungicides on the efficacy of insecticides or vice versa. The insecticides tested were physically compatible with fungicides and no phytotoxic symptoms observed on rice crop when pesticides were applied in combination. Thus, pymetrozine and triflumezopyrim are compatible with test fungicides and can be safely used as tank mix for the simultaneous management of BPH and sheath blightin rice.

Efficacy of a New Combination Insecticide Against Rice Brown Planthopper <i>Nilaparvata Lugens</i> (Stal)

Efficacy of a new combination insecticide against rice brown plant hopper (BPH) Nilaparvata lugens Stal revealed that among all the treatments, significant reduction in the incidence (76.91% reduction over control) and higher grain yield (5.37 ton/ ha) was obtained with buprofezin 24%+ fipronil 40%SC (MAIRM-10) @ 875 ml/ ha. It was at par with buprofezin 24%+ fipronil 40%SC (MAIRM-10) @ 750 ml/ ha followed by buprofezin 25%SC @ 800 ml/ ha. Although maximum grain yield was obtained from buprofezin 24%+ fipronil 40%SC (MAIRM-10) @ 875 ml/ ha, maximum cost benefit in term of ICBR was observed with buprofezin 24%+ fipronil 40%SC (MAIRM-10) @ 750 ml/ ha (1:6.11) besides considering the environmental effect. Buprofezin 24%+ fipronil 40%SC (MAIRM-10) @ 750 ml/ ha was found to be most optimum one for BPH management.

EVALUATION OF THE EFFECT OF ELEVATED CO2 ON BIOEFFICACY OF BUPROFEZIN INSECTICIDE AGAINST BROWN PLANT HOPPER, Nilaparvata lugens (STÅL)

The effect of elevated CO2 (570±25ppm) on the brown plant hopper (BPH) population, rice yield parameters, and efficacy of buprofezin (0.05%) in terms of spray volume was studied in an open top chamber (OTCs) during rainy season 2017 and 2018. The pest population was observed to be higher during 2017 compared to the rainy season of 2018. Under elevated CO2, rice plants had more vegetative tillers (18%) and reproductive tillers (22.1%), but there was a decrease in 1000-seed weight (11.2%), seed number per panicle (3.91%), and grain yield (18.8%) in comparison to ambient CO2 grown rice plants. The spray volumes of 700, 600, 500, and 400 l/ha each caused higher BPH mortality under ambient CO2 compared to elevated CO2. A spray volume of 500 l/ha did not prove as effective under elevated CO2 as under ambient CO2. Lower efficacy of spray volume of 500 l/ha under elevated CO2 could be ascribed to higher canopy size under elevated CO2 due to higher tillering. Increased crop canopy size under elevated CO2 may thus require higher spray volume to ensure proper coverage. Results of the study suggested a need to revise spray volume recommendations to facilitate effective management of BPH under climate change.

Studies on the influence of insecticides and bio-pesticides for the management of Brown plant hopper, Nilaparvata lugens (Stal) in the condition of western U.P. (India)

The experiment was based on the management of Brown plant hopper, important pest of rice. All the given treatment was applied on this pest. The data observed after 3, 7 and days after spray. The observations revealed that all the treatments were found significantly superior over untreated control, Imidacloprid 17.8 SC @ 200 ml/ha were found most effective in comparison to all other treatments. The next effective treatment was Fipronil 5 SC @ 1000 ml/ha followed by Thiamethoxam 25 WG @ 100 g/ha. and in bio-pesticides Metarhizium anisopliae 4.7 × 108 c.f.u./gm @ 2.5 kg/ha.gave the best result among all bio-pesticides. The plot treated by Imidacloprid provide the best Cost benefit ratio (1:7.83) followed by Thiamethoxam 25 WG @ 100 g/ha (1:7.59) Fipronil (1:6.66), Cartap hydrochloride (1:5.59), Beauveria bassiana 2 × 109 c.f.u./gm (1:4.65), Lambda cyhalothrin 5 EC @ 500 ml/ha (1:4.39), Metarhizium anisopliae 4.7 × 108 c.f.u./gm (1:3.83) and Verticellium lacani 2 × 108 c.f.u./ml (1:2.55).

Efficacy of different insecticides against brown planthopper, Nilaparvata lugens (Stål) in rice

The on farm trials were conducted to determine the efficacy of conventional and novel insecticides against brown planthopper (BPH), Nilaparvata lugens (Stål), in rice during kharif 2017 and 2018. All the treatments were effective for BPH management than control. The results of the first year study revealed that the application of Imidacloprid 17.8 SL @ 100 ml ha-1 was found superior by registering lower population of BPH (4.70/ hill) followed by Flonicamid 50 WG @ 150 g ha-1 with 5.67 BPH/hill after 7 days after spray. However, during the second year trial conducted on different insecticides revealed that BPH population was recorded lowest i.e., 3.60 per hill with the application of Buprofezin 25 SC @ 1000 ml ha-1 after 10 days after spray. The effect of this insecticide application was also resulted in the highest grain yield (74.51 q/ha) and maximum benefit cost ratio (6.09).

PENGARUH INSEKTISIDA TERHADAP KEMAMPUAN ADAPTASI WERENG BATANG COKELAT (Nilaparvata lugens Stal) PADA PADI VARIETAS TAHAN

<p><strong><em>Effect of Insecticide</em></strong><strong><em>s</em></strong><strong><em> to Brown Planthopper (</em></strong><strong>Nilaparvata lugens<em> Stal) Adaptation on Resistant Rice Varieties</em></strong><em>.</em> Brown planthopper (BPH) (Hemiptera: Delpachidae) is one of major pests on rice cultivation in Indonesia. Resistant rice varieties and insecticides are commonly used by farmers in BPH management. But, BPH can rapidly adapt on long-term planted varieties and insecticide. The aim of research was to study the ability of insecticide resistance BPH in adaptation on resistant rice varieties. This study was conducted at Indonesian Center for Rice Research from October 2018 to June 2019. BPH<sup>’</sup>s were collected from farmer field and reared for 6th generation. BPH’s were divided into four insecticide population. BPH population sprayed each generation by BPMC (BPMC-BPH), imidacloprid (imidacloprid-BPH), pymetrozine (pymetrozine-BPH), and unsprayed (Control-BPH). In first generation, insecticide resistance conducted to obtain baseline data of BPH resistance to imidacloprid, BPMC and pymetrozine. On 6<sup>th</sup> generation, insecticide resistance test repeated to each population. Four BPH population were tested for the survival rate, fecundity, amount of honeydew, and rice varieties reaction. Result showed that Field population 1st generation were resistance to BPMC and imidacloprid with Resistance Factor (RF) 4.1 and 13.5-fold, respectively, while to pymetrozine was indicate resistance (RF 3.7-fold). In 6th generation, LC<sub>50</sub> all insecticide population were increased, while in Control-BPH were decreased. Inpari 13 still effective againts BPH in all test results. Insecticide resistance-BPH tend to lower adaptation on resistant variety than insecticide susceptible-BPH.</p>

Evaluation of fipronil nanoformulations for effective management of brown plant hopper (Nilaparvata lugens) in rice

ABSTRACTIn this paper, we report the development, characterization and bioefficacy evaluation of fipronil nanoformulations against brown plant hopper (BPH); Nilaparvata lugens in rice. Nanoformulations were characterized for nanosizing and stability under variable conditions. Bioefficacy of nanoformulations were evaluated under field condition at farms of Indian Agricultural Research Institute, New Delhi during Kharif 2015. At milking stage BPH populations were above economic threshold level; followed by foliar application of fipronil nanoformulations at four doses (viz., 30, 45, 60 and 90 g a.i./ha) along with commercial formulation of fipronil. The mean mortality clearly indicated that all the insecticidal treatments were significantly superior over untreated control where, highest mortalities were observed in nanodispersions followed by monolithic dispersion and commercial formulation of fipronil. Treated plots 7 days after application @ 60 g a.i./ha has shown 93.47%, 86.89% and 80.47% reduction BPH population in nanodispersion, encapsulated monolithic dispersion and commercial formulation treated plots respectively. In comparison to commercial formulation @ 60 g a.i./ha yield has increased by 0.56 t ha−1 (28.76%) and 0.26 t ha−1 (14.04%) in nanodispersion and monolithic dispersion.

Insights into the structure–function relationship of brown plant hopper resistance protein, Bph14 of rice plant: a computational structural biology approach

Brown plant hopper (BPH) is one of the major destructive insect pests of rice, causing severe yield loss. Thirty-two BPH resistance genes have been identified in cultivated and wild species of rice Although, molecular mechanism of rice plant resistance against BPH studied through map-based cloning, due to non-existence of NMR/crystal structures of Bph14 protein, recognition of leucine-rich repeat (LRR) domain and its interaction with different ligands are poorly understood. Thus, in the present study, in silico approach was adopted to predict three-dimensional structure of LRR domain of Bph14 using comparative modelling approach followed by interaction study with jasmonic and salicylic acids. LRR domain along with LRR-jasmonic and salicylic acid complexes were subjected to dynamic simulation using GROMACS, individually, for energy minimisation and refinement of the structure. Final binding energy of jasmonic and salicylic acid with LRR domain was calculated using MM/PBSA. Free-energy landscape analysis revealed that overall stability of LRR domain of Bph14 is not much affected after forming complex with jasmonic and salicylic acid. MM/PBSA analysis revealed that binding affinities of LRR domain towards salicylic acid is higher as compared to jasmonic acid. Interaction study of LRR domain with salicylic acid and jasmonic acid reveals that THR987 of LRR form hydrogen bond with both complexes. Thus, THR987 plays active role in the Bph14 and phytochemical interaction for inducing resistance in rice plant against BPH. In future, Bph14 gene and phytochemicals could be used in BPH management and development of novel resistant varieties for increasing rice yield.

Silicon amendment to rice plants impairs sucking behaviors and population growth in the phloem feeder Nilaparvata lugens (Hemiptera: Delphacidae)

The brown planthopper (BPH), Nilaparvata lugens (Stål), is a migratory and destructive sucking insect pest of rice. Silicon (Si) amendment to plants can confer enhanced resistance to herbivores and is emerging as a novel approach for pest management. In the present study, we tested the effects of Si addition at 0.16 (low) and 0.32 (high) g Si/kg soil on sucking behaviors and population growth in BPH. Si amendment increased Si content in rice stems and extended non-probing event and phloem puncture followed by sustained phloem ingestion over that in the no-Si-addition control. High Si addition rate prolonged the stylet pathway and the time needed to reach the first phloem puncture, shortened durations of phloem puncture and phloem ingestion, and decreased the proportion of individuals that produced sustained phloem ingestion. BPH female feeding on and preference for plants with the high Si addition rate were also reduced. As a result, Si application significantly decreased BPH population growth rates while increased population doubling time. These results indicate that Si amendment, especially at the high rate, confers enhanced rice plant resistance to BPH through impairment of BPH feeding. Our results highlight the potential of Si amendment as an alternative for BPH management.

Ready-mix formulation of buprofezin 23.1%+fipronil 3.85% SC for eco-friendly and economic management of brown plant hopper in rice

The present study was undertaken to evaluate the field effectiveness vis.-a-vis. non-target toxicity of ready mix formulation of an insect growth regulator buprofezin and one phenylpyrazole fipronil against brown plant hopper, Nilaparvata lugens (Stal.) of rice during rabi 2014–15 and kharif 2015. The results revealed that buprofezin 23.1% + fipronil 3.85% SC at higher dosages effectively reduced the brown plant hopper population during the first and second season (0.00–21.33 and 0.00–24.33 number of nymphs and adults per 3 hills) as compared to standard check molecules (9.00–26.26 and 10.00–34.08 number of nymphs and adults per 3 hills), respectively. Highest mean per cent reduction of brown plant hopper population was encountered in buprofezin 23.1%+fipronil 3.85% SC @ 875 (75.4 and 81.38% during first and second season) and 750 (72.5 and 76.34% during first and second season) ml/ha, respectively, during both the seasons. The test chemistry at lower to medium dosages found very soft against the predatory fauna viz., Cyrtorhinus lividipennis, Oxyopes spp. and Lycosa spp. with mean per cent mortality of less than 5% during both the seasons. Highest yield was obtained from the higher dosages of buprofezin 23.1%+fipronil 3.85% SC (48.85 and 50.88 q/ha) as compared to standard checks (36.04 39.61 q/ha), whereas highest benefit was registered by the test chemistry at 750 ml/ha (1: 5.79) which was considered as the recommended dose for the farming community from pest management, eco-toxicology and economic point of view.

Recent progress on the genetics and molecular breeding of brown planthopper resistance in rice.

Brown planthopper (BPH) is the most devastating pest of rice. Host-plant resistance is the most desirable and economic strategy in the management of BPH. To date, 29 major BPH resistance genes have been identified from indica cultivars and wild rice species, and more than ten genes have been fine mapped to chromosome regions of less than 200 kb. Four genes (Bph14, Bph26, Bph17 and bph29) have been cloned. The increasing number of fine-mapped and cloned genes provide a solid foundation for development of functional markers for use in breeding. Several BPH resistant introgression lines (ILs), near-isogenic lines (NILs) and pyramided lines (PLs) carrying single or multiple resistance genes were developed by marker assisted backcross breeding (MABC). Here we review recent progress on the genetics and molecular breeding of BPH resistance in rice. Prospect for developing cultivars with durable, broad-spectrum BPH resistance are discussed.

High levels of silicon provided as a nutrient in hydroponic culture enhances rice plant resistance to brown planthopper

Silicon plays a significant role in the resistance of rice plants to multiple stresses including diseases and pests. However, there has been little research on the effect of silicon application on plant resistance to brown planthopper (BPH), Nilaparvata lugens Stål, (Homoptera: Delphacidae), in rice (Oryza sativa L.). In the present work, experiments were conducted in greenhouses to study the impact of rice plants grown in hydroponic culture and fed with high concentrations of silicon (240 mg/L SiO2) as a macronutrient on the performance of the phloem-feeding insect, BPH. It appeared that a high silicon concentration had no significant effects on the phenotypic performance of two rice lines. However, the BPH survival rate and settled insect number on one of the rice lines treated with high silicon concentrations decreased significantly from 8 and 4 day points, respectively, after their release. A similar downward trend was observed on the other rice line treated with a high concentration silicon solution from the 24 h time point. Furthermore, BPH insects on both rice lines treated with high silicon concentrations were significantly less fertile and excreted less honeydew compared to controls. In conclusion, high silicon had significant antibiotic and antixenotic effects on BPH in the two rice lines when compared to controls. We conclude that silicon is one of the main factors that restrict BPH performance in rice-BPH interactions, and it is potentially of great benefit for non-pesticide BPH management.

Decrease of insecticide resistance over generations without exposure to insecticides in Nilaparvata lugens (Hemipteran: Delphacidae).

The brown planthopper, Nilaparvata lugens (Stål), is one of the most important insect pests on paddy rice in tropical and temperate Asia. Overuse and misuse of insecticides have resulted in the development of high resistance to many different insecticides in this pest. Studies were conducted to evaluate the change of resistance level to four insecticides over 15 generations without any exposure to insecticides in brown planthopper. After 15 generations' rearing without exposure to insecticide, brown planthopper could reverse the resistance to imidacloprid, chlorpyrifos, fipronil, and fenobucarb. The range and style of resistance reversal of brown planthopper differed when treated with four different insecticides. To monitor potential changes in insect physiological responses, we measured the activity of each of the three selected enzymes, including acetylcholinesterases (AChE), general esterases (EST), and glutathione S-transferases. After multiple generations' rearing without exposure to insecticide, AChE and EST activities of brown planthopper declined with the increased generations, suggesting that the brown planthopper population adjusted activities of EST and AChE to adapt to the non-insecticide environment. These findings suggest that the reducing, temporary stop, or rotation of insecticide application could be incorporated into the brown planthopper management.

Susceptibility to Insecticides and Ecological Fitness in Resistant Rice Varieties of Field Nilaparvata lugens Stål Population Free from Insecticides in Laboratory

A population of rice brown planthopper (BPH) Nilaparvata lugens collected from a paddy field in Hangzhou was successively reared on susceptible rice Taichung Native 1 (TN1) in a laboratory free from insecticides for more than 14 generations. The changes in susceptibility to insecticides and ecological fitness on different resistant rice varieties were monitored in each generation. The resistance ratio to imidacloprid sharply declined with the succession of rearing generations without insecticides from 359.94-fold at F1 to 6.50-fold at F14 compared with the susceptible strain, and the resistance ratio to chlorpyrifos was from 9.90-fold at F1 to 5.94-fold at F14. Nymphal duration and weights of newly hatched female adults were significantly affected by rice variety, generation and their interactions, but nymphal survival was significantly affected by the generation only. The ratio of brachypterous adults in males was affected by the generation and generation × variety interaction, whereas no difference was found in females. Nymphal duration extended with increasing generations, and the female nymphal duration was shorter in the susceptible variety TN1 than those in the resistant varieties IR26 and IR36. In addition, the female adult weight in TN1 was higher than those in IR26 and IR36. These results indicated that the resistance of field BPH population to insecticides was reversed after several generations of no-exposure to insecticides, and the ecological fitness in TN1 was higher than those in IR26 and IR36. These findings suggested the rational and reduced use of insecticides in combination with the manipulation of resistant rice varieties would be effective for BPH management.

Reaction of resistant and susceptible rice genotypes against brown planthopper (Nilaparvata lugens)

The study was carried out to assess the reaction of different rice genotypes in response to brown planthopper (BPH)Nilaparvata lugens (Stal.) attack and the possible use of these genotypes in BPH management. The resistant genotypes PTB 33, ADT 45 and ASD 7 and the moderately resistant genotypes CO 43 and KAU 1661 recorded the lowest nymphal preference, fecundity, feeding rate, survival, growth index, population buildup and plant dry weight loss per mg of insect dry weight produced, and more unhatched eggs, longer nymphal development period, days to wilt and higher Functional Plant Loss Index compared with the susceptible genotype TN1. In resistant and moderately resistant genotypes, a greater accumulation of defense enzymes such as peroxidase and polyphenol oxidase in response toN. lugens infestation was recorded one day after infestation, and more pathogenesis-related protein and chitinase activity was noted 3 days after infestation. The activity was sustained for more than a week after infestation compared with the susceptible genotype TN1.