Major Pest Of Rice Research Articles

Expression of lima bean terpene synthases in rice enhances recruitment of a beneficial enemy of a major rice pest.

Volatile terpenoids play a key role in plant defence against herbivory by attracting parasitic wasps. We identified seven terpene synthase genes from lima bean, Phaseolus lunatus L. following treatment with either the elicitor alamethicin or spider mites, Tetranychus cinnabarinus. Four of the genes (Pltps2, Pltps3, Pltps4 and Pltps5) were up-regulated with their derived proteins phylogenetically clustered in the TPS-g subfamily and PlTPS3 positioned at the base of this cluster. Recombinant PlTPS3 was able to convert geranyl diphosphate and farnesyl diphosphate to linalool and (E)-nerolidol, the latter being precursor of the homoterpene (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT). Recombinant PlTPS4 showed a different substrate specificity and produced linalool and (E)-nerolidol, as well as (E,E)-geranyllinalool from geranylgeranyl diphosphate. Transgenic rice expressing Pltps3 emitted significantly more (S)-linalool and DMNT than wild-type plants, whereas transgenic rice expressing Pltps4 produced (S)-linalool, DMNT and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT). In laboratory bioassays, female Cotesia chilonis, the natural enemy of the striped rice stemborer, Chilo suppressalis, were significantly attracted to the transgenic plants and their volatiles. We further confirmed this with synthetic blends mimicking natural rice volatile composition. Our study demonstrates that the transformation of rice to produce volatile terpenoids has the potential to enhance plant indirect defence through natural enemy recruitment.

Higher Fertilizer Inputs Increase Fitness Traits of Brown Planthopper in Rice

Rice (Oryza sativa L.) is the primary staple food source for more than half of the world’s population. In many developing countries, increased use of fertilizers is a response to increase demand for rice. In this study, we investigated the effects of three principal fertilizer components (nitrogen, phosphorus and potassium) on the development of potted rice plants and their effects on fitness traits of the brown planthopper (BPH) [Nilaparvata lugens (Stål) (Homoptera: Delphacidae)], which is a major pest of rice in Bangladesh and elsewhere. Compared to low fertilizer inputs, high fertilizer treatments induced plant growth but also favored BPH development. The BPH had higher survival, developed faster, and the intrinsic rate of natural increase (rm) was higher on well-fertilized than under-fertilized plants. Among the fertilizer inputs, nitrogen had the strongest effect on the fitness traits of BPH. Furthermore, both the “Plant vigor hypothesis” and the “Plant stress hypothesis” were supported by the results, the former hypothesis more so than the latter. These hypotheses suggest that the most suitable/attractive hosts for insect herbivores are the most vigorous plants. Our findings emphasized that an exclusive focus on yield increases through only enhanced crop fertilization may have unforeseen, indirect, effects on crop susceptibility to pests, such as BPH.

Development of a Sri Lankan rice variety Bg 94-1 harbouring cry2A gene of Bacillus thuringiensis resistant to rice leaffolder [Cnaphalocrocis medinalis (Guenée)

The rice leaffolder (RLF) [ Cnaphalocrocis medinalis (Guenee)] is a major lepidopteran insect pest of rice in Sri Lanka and the larvae cause significant yield losses annually. Insecticidal crystal protein gene, cry2A driven by the 35S cauliflower mosaic virus (CaMV) promoter with a double enhancer sequence was transformed into scutellum derived embryogenic calli of Bg 94-1 via Agrobacterium tumefaciens mediated transformation procedure. Transformation vector pCAMBIA 1305.1 containing the transgene construct CaMV 35S d-cry2A-NOS, hygromycin phosphotransferase and β-glucuronidase (GUS)-Plus was employed in this study. Transformed calli were subjected to 4 ‒ 5 rounds of hygromycin selection. Molecular analysis of the generated plants together with an insect bioassay using RLF larvae confirmed successful transformation and expression of this transgene in T0 generation of rice plants. A total of 19 putative transgenic plants could be confirmed from a total of 60 T0 generation plants examined. Insect feeding bioassay demonstrated that T0 transgenic rice plants are effective against RLF larvae, and showed approximately 89 % larval mortality after 3 days and 100 % mortality after 5 days of feeding. Further molecular analysis of T1 generation of the transgenic lines confirmed the stable integration of cry2A transgene into the Bg 94-1 genome. Findings of this study demonstrated that the cry2A gene of Bacillus thuringiensis ( Bt ) was successfully transformed into Bg 94-1 via Agrobacterium mediated transformation and have developed resistance against the RLF larvae. Thus, this study highlights the importance of developing transgenic rice, which can provide insect resistance against a major lepidopteran insect pest of rice in Sri Lanka.

The effect of gamma radiation on sterility and mating ability of brown planthopper, Nilaparvata lugens(Stål) in field cage

The brown planthopper, Nilaparvata lugens(Stål) is the major rice pest in Thailand. Adults and nymphs suck the sap from the rice plant causing it to wilt and transmitting the grassy stunt and the ragged stunt diseases. The population suppression by the sterile insect technique is overwhelmingly a function of mating between sterile males and wild females. The objectives of these experiments were to determine the suitable dose which induces partially sterile in N. lugens and their effect on wild population in the field cages. One-day-old 4th and 5th instar nymphs and adults were irradiated in a 60Co irradiator at the doses of 30, 60, 90 and 120 Gy. It was found that irradiation at the dose of 90 Gy induced complete sterility in female and 78.47 % sterility in males. The inherited sterility were transferred to their progenies and induced 51.46 and 77.00 % sterility in F-1 males and females. The irradiation as the mention dose did not affect mating ability. The competitiveness index was increased when the ratio of irradiated males per normal male was increased. The releasing irradiated males at 10 fold of normal males in field cages could suppress F-1 population 80.11 % and suppress F-2 population 80.32 % when compare with the control. This technique may be applied to delay and/or reduce seasonal increase of brown planthopper.

Populasi Hama Wereng Batang Coklat (Nilaparvata lugens Stal.), Keragaman Musuh Alami Predator Serta Parasitoidnya Pada Lahan Sawah Di Dataran Rendah Kabupaten Indramayu

Population of brown plant hopper (Nilaparvata lugens Stal) is one of the major rice pest that is threatening rice production in Indramayu. Integrated pest management is needed to control the population of brown plant hopper (BPH). To construct effective strategy of Integrated Pest Management, a survey to obtain information about the population of BPH and the diversity of its natural enemies predator and parasitoid is required. The result of the survey showed that fluctuation of BPH population was evidence. BPH occurs from the 1st week of observation and the population was rising until the 5th week of observation and hence the population declined until the 12th week of observation. This population decline was caused by BPH’s live cycle followed the growth phase of rice plant. Correlation between climate factors and fluctuation of BPH population was not significant. Based on Shanon-Wiener diversity index analysis, the diversity of natural predators of BPH was medium with the value of H’ of 1,83 due to uniform field condition

Present status on bio-ecology and management of tobacco caterpillar, Spodoptera litura (Fabricius) – An update

The tobacco caterpillar, Spodoptera litura (Fabricius) is one of the economically important and regular polyphagous pests on the field and horticultural crops and distributed in Indo-Australian tropics. The larvae feed on a wide range of plants and have been recorded from over 40 mostly dicotyledonous plant families. It is a major pest of tobacco, cotton, rice, maize, soybean and groundnut. The present article focuses on literature generated on various aspects of tobacco caterpillar viz., pest status and their distribution, biology, damage, losses, seasonal incidence, host range and ecology and different management strategies such as, cultural and mechanical, host plant resistance, role of natural enemies and need based chemical control besides integrated pest management strategies employed against this pest.

Point mutations in acetylcholinesterase 1 associated with chlorpyrifos resistance in the brown planthopper, Nilaparvata lugens Stål.

Insecticide resistance frequently results from target-site insensitivity, such as point mutations in acetylcholinesterases (AChEs) for resistance to organophosphates and carbamates. From a field-originated population of Nilaparvata lugens, a major rice pest, a resistant population (R9) was obtained by nine-generation continuous selection with chlorpyrifos. From the same field population, a relatively susceptible population (S9) was also constructed through rearing without any insecticides. Compared to thesusceptible strain, Sus [medium lethal dose (LC50 ) = 0.012 mg/l], R9 had a resistance ratio (RR) of 253.08-fold, whereas the RR of S9 was only 2.25-fold. Piperonyl butoxide and triphenyl phosphate synergized chlorpyrifos in R9 less than three-fold, indicating other important mechanisms for high resistance. The target-site insensitivity was supported by the key property differences of crude AChEs between R9 and S9. Compared to S9, three mutations (G119S, F331C and I332L) were detected in NlAChE1 from individuals of the R9 and field populations, but no mutation was detected in NlAChE2. G119S and F331C could decreased insecticide sensitivities in recombinant NlAChE1, whereas I332L took effect through increasing the influence of F331C on target insensitivity. F331C might be deleterious because of its influence on the catalytic efficiency of NlAChE1, whereas I332L would decrease these adverse effects and maintain the normal functions of AChEs.

RNA interference knockdown of aminopeptidase N genes decrease the susceptibility of Chilo suppressalis larvae to Cry1Ab/Cry1Ac and Cry1Ca-expressing transgenic rice

Transgenic rice expressing Bacillus thuringiensis (Bt) Cry toxins are resistant to lepidopteran pests, such as Chilo suppressalis, a major insect pest of rice in Asia. Understanding how these toxins interact with their hosts is crucial to understanding their insecticidal action. In this study, knockdown of two aminopeptidase N genes (APN1 and APN2) by RNA interference resulted in decreased susceptibility of C. suppressalis larvae to the Bt rice varieties TT51 (Cry1Ab and Cry1Ac fusion genes) and T1C-19 (Cry1Ca), but not T2A-1 (Cry2Aa). This suggests that APN1 and APN2 are receptors for Cry1A and Cry1C toxins in C. suppressalis.

Video monitoring of brown planthopper predation in rice shows flaws of sentinel methods

Immobilized preys are routinely used in agro-ecological exposure studies to quantify predation of pests under field conditions, but this method has not been validated. Our purpose was to determine the validity of using immobilized adults of the major rice pest Nilaparvata lugens, brown plant hopper (BPH), as sentinels. We used direct observation by video recording to determine the causal agents of removal of field exposed BPH sentinels with two experiments: 1) we recorded removal events of dead, immobilized BPH; and 2) we compared removal of (i) dead, immobilized BPH, (ii) live, immobilized BPH, and (iii) live, mobile BPH. Long-horned grasshoppers were responsible for most removals of dead, immobilized BPH, in both experiments. Predatory ground beetles removed most of the live, immobilized BPH, whereas frogs were the major predators of live, mobile BPH. Overall, we showed that removal of immobilized sentinel prey is not representative for predation of live, mobile prey, stressing the need for a critical assessment of commonly used sentinel methods. In addition, we found that frogs played the major role in predation of BPH in rice. As current strategies to enhance biocontrol of planthoppers in rice focus on arthropod natural enemies, this finding could have major implications.

Reference genes for quantitative real-time PCR analysis in symbiont Entomomyces delphacidicola of Nilaparvata lugens (St\xe5l)

Nilaparvata lugens (Stål) (Hemiptera: Delphacidae) is a major rice pest that harbors an endosymbiont ascomycete fungus, Entomomyces delphacidicola str. NLU (also known as yeast-like symbiont, YLS). Driving by demand of novel population management tactics (e.g. RNAi), the importance of YLS has been studied and revealed, which greatly boosts the interest of molecular level studies related to YLS. The current study focuses on reference genes for RT-qPCR studies related to YLS. Eight previously unreported YLS genes were cloned, and their expressions were evaluated for N. lugens samples of different developmental stages and sexes, and under different nutritional conditions and temperatures. Expression stabilities were analyzed by BestKeeper, geNorm, NormFinder, ΔCt method and RefFinder. Furthermore, the selected reference genes for RT-qPCR of YLS genes were validated using targeted YLS genes that respond to different nutritional conditions (amino acid deprivation) and RNAi. The results suggest that ylsRPS15p/ylsACT are the most suitable reference genes for temporal gene expression profiling, while ylsTUB/ylsACT and ylsRPS15e/ylsGADPH are the most suitable reference gene choices for evaluating nutrition and temperature effects. Validation studies demonstrated the advantage of using endogenous YLS reference genes for YLS studies.

A salivary EF-hand calcium-binding protein of the brown planthopper Nilaparvata lugens functions as an effector for defense responses in rice

The brown planthopper (BPH), Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), a major pest of rice in Asia, is able to successfully puncture sieve tubes in rice with its piercing stylet and then to ingest phloem sap. How BPH manages to continuously feed on rice remains unclear. Here, we cloned the gene NlSEF1, which is highly expressed in the salivary glands of BPH. The NlSEF1 protein has EF-hand Ca2+-binding activity and can be secreted into rice plants when BPH feed. Infestation of rice by BPH nymphs whose NlSEF1 was knocked down elicited higher levels of Ca2+ and H2O2 but not jasmonic acid, jasmonoyl-isoleucine (JA-Ile) and SA in rice than did infestation by control nymphs; Consistently, wounding plus the recombination protein NlSEF1 suppressed the production of H2O2 in rice. Bioassays revealed that NlSEF1-knockdown BPH nymphs had a higher mortality rate and lower feeding capacity on rice than control nymphs. These results indicate that the salivary protein in BPH, NlSEF1, functions as an effector and plays important roles in interactions between BPH and rice by mediating the plant’s defense responses.

Phylogeography of the Asian rice gall midge Orseolia oryzae (Wood Mason) (Diptera: Cecidomyiidae) in Thailand.

The Asian rice gall midge (RGM) Orseolia oryzae (Wood Mason) (Diptera: Cecidomyiidae) is a major pest of rice, leading to yield losses in Thailand and many Asian countries. Despite an increasing number of reported midge outbreaks and the presence of many susceptible rice varieties, only a few studies have focused on the genetic variation of the midges. Therefore, we analyzed the phylogeography among Thai RGM populations covering north, northeast and central Thailand. Two mitochondrial DNA genes, cytochrome C oxidase I (COI) and 12S, and a non-coding repeat region (RR) situated just before COI were amplified. Overall, the haplotype diversity for COI and 12S genes of the Thai population was high, but the nucleotide diversity was quite low. Altogether, the phylogenetic tree and pairwise F st values indicated that Thai RGM populations recently expanded and were homogeneously distributed throughout the country, except for some populations in the north, which most likely became recently isolated from the main population. Two non-coding repeat motifs, that were recently observed in the mitogenome of RGM in India, were absent in Thai populations and replaced by an 89bp non-coding sequence. Tandem nucleotide repeats of the sequence TA were also observed. The repeat copy number varied from 2 to 11 and was not correlated with geographical repartition of the midge. Finally, COI barcoding divergence between Indian and Thai populations was high (6.3% in average), giving insights into the potential existence of an RGM species complex in Asia.

A Study of the African White Rice Stem Borer (Maliarpha separatella Rag.) Population Density Fluctuations at Mwea Irrigation Scheme in Central Kenya

The African white rice stem borer (Maliarpha separatella Ragonot) is a major pest of rice in Kenya. To understand and develop appropriate management packages, its population dynamics were studied at Mwea irrigation scheme in Central Kenya. This was for two wet and two dry periods. Farmer fields located in different parts of the scheme and outside the scheme were sampled every fortnight. Farms sampled represented five water provision schedules (System of Rice intensification (SRI), rain fed, flood irrigated, sporadic irrigation, and fallow period). Five planting regimes (on season, off season double cropping, ratoon, and late planting) and three management styles (controlled by National Irrigation Board (N.I.B), not controlled by N.I.B and out-growers) were studied. During each sampling, a 1mx1m quadrant was used randomly and pest counted on all the plants within the quadrant. Results showed that the number of M. separatella varied significantly (p<0.05) in the scheme. Pest densities were highest in off season planted rice (13.1). High numbers were also found in Non N.I.B controlled fields with sporadic irrigation (8.1) and the lowest in the N.I.B, fallow (2.5) and this was significant (p<0.05). There were no significant differences in pest infestations on the normal season crop (0.3) and the ratoon crop (0.6) p<0.05 and SRI and conventional irrigated fields (p<0.05). From the results it is recommended that off season planting of rice be discouraged and that efforts are made to ensure that farmers synchronize planting dates and other cultural practices for the crop, within the scheme and in rice farms outside the scheme.

Field Efficacy of Certain New Insecticides against Major Insect Pests of Rice at Manipur

Field experiment conducted during kharif, 2012 and 2013 at the Rice Research Farm of the College of Agriculture, Central Agricultural University, Imphal evaluated the efficacy of certain new insecticides against the rice pests viz., Asian gall fly (Orseolia oryzae Wood-Mason), yellow stem borer (Scirpophaga incertulas Walker), leaf folder (Cnaphalocrocis medinalis Guenee) and whorl maggot (Hydrellia philippina Ferino). Against the gall fly, thiamethoxam 25 WG @ 25 g a.i. ha1 was found effective. This was followed by imidacloprid 70 WG @ 50 g a.i. ha−1(4.40% SS) and acephate 50 + imidacloprid 1.8% (Lancergold) 51.8 SP @ 500 g a.i. ha−1 but insignificantly. Flubendiamide 39.35 SC @ 24 g a.i. ha−1 was also found effective against the leaf folder and yellow stem borer with the least leaf damage (LD), dead heart (DH) and white ear head (WEH). It was followed by chlorantraniliprole 18.35 SC @ 30 g a.i.ha−1 and thiamethoxam 25 WG @ 25 g a.i. ha−1 which showed insignificant difference. Against the whorl maggot, thiamethoxam 25 WG @ 25 g a.i. ha−1 was found the best, closely followed by acephate 50% + imidacloprid 1.8%. Maximum grain yield (5.00 t ha−1) was obtained from the plots treated with flubendiamide 39.35 SC, and it was found insignificantly differing from thiamethoxam 25 WG (5.00 t ha−1), at par with acephate 50% + imidacloprid 1.8% 51.8SP (4.83 t ha−1), fipronil 5 SC (4.72 t ha−1) and flubendiamide 39.35 SC (4.68 t ha−1). Thiocloprid 21.7 SC gave the least grain yield. The net profit varied from Rs 2353 (thiacloprid 21.7 SC) to Rs. 17288 (thiamethoxam 25 WG) with the cost: benefit ratios ranging from 1: 0.45 to 1: 10.79, the minimum and maximum being with thiacloprid 21.7 SC and thiamethoxam 25 WG, respectively.

Genetic diversity of rice stem borer (Chilo suppressalis Walker) from Northern Iran and comparison with other countries

Rice striped stem borer, &lt;em&gt;Chilo suppressalis&lt;/em&gt; Walker (Lepidoptera: Crambidae) is considered the major pest of rice in Iran. Because of the serious damage on rice in Northern Iran, the present study was conducted to investigate genetic diversity within populations of &lt;em&gt;C. suppressalis&lt;/em&gt;, from Mazandaran using a template of cytochrome oxidase I gene, 750 bps, (&lt;em&gt;COI&lt;/em&gt;). Later the haplotypes from Iran were compared with those found in other countries. According to the results of this study, there is very low genetic diversity (two haplotypes) among different populations of this pest in populations of Northern Iran. The genetic similarity and low levels of genetic diversity of these populations suggest that the pest colonization occurred relatively recently and there is high gene flow between these populations of the province. In addition, haplotypes of Mazandaran province are different with those found in other countries. The similarity of Iranian population (Simorgh) with one population from China indicated that China might be the origin of &lt;em&gt;C. suppresalis&lt;/em&gt;.

Effects of Nitrogen, Phosphorous and Potassium on Host-Choice Behavior of Brown Planthopper, Nilaparvata lugens (Stål) on Rice Cultivar

The brown planthopper (BPH), Nilaparvata lugens (Stal) (Homoptera: Delphacidae) is a major pest of many rice growing countries worldwide. It has been observed that one rice field is severely infested by BPH while an adjacent field left untouched. We hypothesized that differences in nutrient content in rice plants may explain this behavior. BPH feeding and oviposition behavior was evaluated on rice plants that had been grown under a range of fertilizer treatments. Tissue samples from experimental rice plants were analyzed for percent N, P, K, Si, free sugars and soluble proteins which were regressed with BPH host choice parameters. A completely randomized design with four replications in a factorial scheme was used in experiments where levels of soil N, P and K were taken as factors. Nymph feeding preference did not differ significantly among different nutrient treated rice plants. Adult females preferred to feed and oviposit on rice plants fertilized with N but it showed negative preference with K supplementation, while P had no marked effect. The position of feeding and ovipositing shifted gradually from lower to upper of leaf sheath and then to leaf blade with decrease of N fertilization to the rice plant. Host choice of BPH for feeding and ovipositing were positively associated with plant tissue concentrations of N, total free sugars and soluble proteins, negatively with Si but not with P and K. Plant tissue biochemical those are associated with BPH host preference may regulate how fast and where they settle on a rice plant.

Electrophysiological and behavioral responses of female African rice gall midge, Orseolia oryzivora Harris and Gagné, to host plant volatiles.

African rice gall midge, Orseolia oryzivora Harris and Gagné, is a major pest of rice in Africa. Depsite its economic importance, its chemical ecology is not well understood. Here, we assessed behavioral and electrophysiological responses of O. oryzivora to host plant volatiles. In olfactometer bioassays, mated female O. oryzivora were attracted to volatiles emitted from intact rice plants but were repelled by volatiles collected from plants infested by conspecifics. In a choice test, there was a preference for volatiles from uninfested plants over those from infested plants. Coupled gas chromatography-electroantennography analyses of panicle volatiles isolated four electrophysiologically active components: (S)-linalool, 4,8-dimethyl-1,3,7-nonatriene, (E)-caryophyllene, and (R/S)-(E)-nerolidol. A synthetic blend of volatiles at the same concentration and ratio as that from an intact plant was attractive to mated females, whereas a blend based on the ratio of volatiles from an infested plant was repellent. This suggests that O. oryzivora uses olfaction for host plant recognition. The identification of blends of volatiles emitted by plants that can both attract and repel O. oryzivora may aid the development of sustainable control measures.

RNAi in the striped stem borer, Chilo suppressalis, establishes a functional role for aminopeptidase N in Cry1Ab intoxication

The striped stem borer, Chilo suppressalis, is a major target pest of transgenic rice expressing the Cry1Ab protein from the bacterium Bacillus thuringiensis (Bt) in China. Evolution of resistance in this pest is a major threat to the durability of Bt rice. Since Bt exerts its activity through binding to specific receptors in the midgut of target insects, identification of functional Cry1Ab receptors in the midgut of C. suppressalis larvae is crucial to evaluate potential resistance mechanisms and develop effective strategies for delaying insect resistance. In this work, we identified the putative Cry1Ab toxin-binding protein, aminopeptidase-N (APN), in the midgut of C. suppressalis by ligand blot and mass spectrometry. After cloning the full-length cDNAs encoding APN isoforms from the C. suppressalis larval midgut, we studied their spatiotemporal expression in different gut tissues and developmental stages. Furthermore, RNA interference (RNAi) against C. suppressalis aminopeptidases (CsAPNs) was employed to illustrate a functional role for CsAPNs in Cry1Ab toxicity to C. suppressalis larvae using injection and oral delivery of Stealth™ siRNA. Down-regulating the expression of CsAPNs by RNAi was closely associated with reduced susceptibility of C. suppressalis to Cry1Ab. These data provide the first direct evidence that CsAPNs participate in the mode of Cry1Ab action and may act as the functional receptor of Cry1A in C. suppressalis larvae.

Evaluation of thiamethoxam 25 per cent WG against major insect pests of rice (Oryza sativa L.)

An experiment was conducted at Regional Agriculture Research Station, College of Agriculture, Waraseoni, Bagalaght, Madhya Pradesh during the 2014-15 to study on the evaluation of Thiamethoxam 25 per cent WG for the management of stem borer (Scirpophaga incertulasWalker), leaf folder (Cnaphalocrocis medinalis Guenee), gall midge (Orseolia oryzaeWood Mason), leaf hoppers viz., green leaf hopper (Nephotettix virescens Distant), brown plant hopper (Nilaparvata lugens Stal), in rice crop. Thiamethoxam 25 per cent WG used in the experiment was different doses i.e. @ 20 g a.i. /ha, 25 g a.i. /ha, 30 g a.i. /ha, 50 g a.i. /ha, and 100 g a.i. /ha, with insecticidal check Imidacloprid 17.8 SL @ 30 ml a.i./ha. Two sprays of insecticides were applied at fifteen days interval. The most effective dose of thiomethoxam 25 per cent WG in controlling the rice insect pests was 50 g. a.i./ha followed by 30 g a.i. /ha and 25 g a.i. /ha. Per cent reduction of insect pests over untreated plot after final sprays was followed this order of efficacy: Thiamethoxam 25 per cent WG @ 20 g a.i. /ha> 100 g a.i. /ha, > Imidacloprid 17.8 SL @ 30 ml a.i./ha.. Highest cost benefit ratio (1:21.69) was observed in thiamethoxam 50 per cent WG @ 20 g a.i. /ha. How to view point the article : Panse, Raju Kumar, Bhandarkar, A.P. and Rajak, S.K. (2016). Evaluation of thiamethoxam 25 per cent WG against major insect pests of rice (Oryza sativa L.). Internat. J. Plant Protec., 9(2) : 551-555, DOI : 10.15740/HAS/IJPP/9.2/551-555.

Insect diversity and extent of infestation of major rice pests in Burdwan district, West Bengal, India

Insects collected from different rice fields of Burdwan District of West Bengal from February 2012 to November 2014 by light trapping, netting, sweeping or hand picking method recorded 32 species of arthropods under eight orders. The population of rice leaf folder, yellow stem borer, striped stem borer, army worm, hispa, brown plant hopper, green leaf hopper, gandhi bug and grasshoppers were found to be 7.95/hill and 7.86/hill; 2.36/hill and 1.62/hill; 0.19/hill and 0.27/hill; 0.98/hill and 0.73/hill; 0.87/hill and 1.04/hil; 4.89/hill and 3.47/hill; 4.24/hill and 3.76/hill; 2.15/hill and 2.68/hill; 4.17/hill and 3.82/hill in Galsi and Memari, respectively. Infestation of the crop and population of C. medinalis and S. incertulas in the rice fields at different locations of Galsi and Memari during dry and wet season in 2012, 2013 and 2014 were studied. Leaffolders were more prevalent in wet season than dry season. During the dry season of 2012, 2013 and 2014 the infestation of S. incertulas and the population of larvae in the rice fields were 90.24 - 90.47; 90.12 - 92.50; 89.56 - 91.98 percent and 7.00 - 7.33; 7.00; 6.33 - 7.00 per hill respectively. During the wet season of 2012, 2013 and 2014, the infestation and population of S. incertulas in the rice fields were 73.01 - 75.90; 68.44 - 70.1; 74.56 - 77.3 percent and 3.00 - 3.33; 2.67 - 3.67; 3.33 - 3.67 larvae per hill, respectively.