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Articles by T. Ramasubramanian
Total Records ( 6 ) for T. Ramasubramanian
  Rang Lal Meena , T. Ramasubramanian , S. Venkatesan and S. Mohankumar
  The presence of Tospovirus in thrips vector, Scirtothrips dorsalis has been detected for the first time in India using RT- PCR analysis. Similarly RT-PCR analysis with GBNV infected tomato leaves also resulted in the amplification of cDNA corresponding to the N gene (approximately 830 bp) of Coimbatore isolate. Dendrogram constructed on the basis of RAPD similarity matrix revealed that S. dorsalis population from tomato, groundnut and chillies had atleast 75% similarity while; only 50 % similarity existed between the Frankliniella schultzei populations from cowpea and sunnhemp. Thrips tabaci from cotton was distantly related with S. dorsalis and Frankliniella schultzei with lowest similarity indices (less than 0.464). This was also confirmed by the ISSR analysis with the same six thrips populations. It is evident from the present study that RAPD markers were more informative than ISSR in differentiating host-associated populations of thrips.
  T. Ramasubramanian and A. Regupathy
  Resistance to thiodicarb was diagnosed in the field population of Helicoverpa armigera from Tamil Nadu, India. Bouquet bioassay results in the laboratory indicated the level of resistance was 30.0 - 45.0% at recommended dose (1000g.a.i ha-1) of thiodicarb. The suppression of larval population and reduction of damage to bolls, squares, locules and kapas in the field also in agreement with the laboratory results.
  T. Ramasubramanian and A. Regupathy
  The relative fitness of pyrethroid selected populations of Helicoverpa armigera was studied by construction of age specific fecundity tables for F2,F7 and F14 generations of unselected, fenvalerate and cypermethrin selected populations. The net reproductive rate computed from the life table statistics indicated that the fitness of the pyrethroid selected populations decreased drastically as the population advanced to fourteenth generation. In F2 the net reproductive rate was 237.437, 231.359 and 228.24 for the unselected, fenvalerate and cypermethrin selected populations respectively. It came down to 123.677 and 121.432 for fenvalerate and cypermethrin selections respectively and only a marginal decline to 197.962 in unselected population. The decrease in fitness was greatly manifested through reproductive behaviour but not by the developmental traits. The variation in generation time was insignificant between the selected and unselected populations irrespective of the generations.
  T. Ramasubramanian
  The magnitude of pyrethroid resistance was very high throughout India irrespective of the Helicoverpa armigera strains. The mechanism of pyrethroid resistance in H. armigera varies across the different regions of India, but PBO suppressible resistance (MFO mediated) appeared to be the major mechanism and the role played by carboxyl esterase was only marginal. Nerve insensitivity mechanism was observed in strains from areas where, the selection pressure from pyrethroids was intense over the past one decade. Since the pyrethroid resistance is more aggressive in India, several resistant management strategies were discussed in this review.
  T. Ramasubramanian and A. Regupathy
  The bouquet bioassay experiments under laboratory condition revealed that the percentage mortality of Helicoverpa armigera was more than 70% even at the lowest rate of 10 g a.i ha-1 (1/10th recommended dose) and the percentage survival was in the range of just 7.5-20.0% at the recommended dose of indoxacarb. Good biological efficacy of this new molecule was also reflected in the suppression of larval population and reduction of damage to bolls, squares, locules and kapas in the field. The increased susceptibility of pyrethroid resistant populations of H. armigera to indoxacarb in Tamil Nadu could be due to the activation by carboxyl esterases in to its more toxic metabolite.
  T. Ramasubramanian , K. Ramaraju and A. Regupathy
  Tetranychus urticae is known to have a high tendency to develop resistance to acaricides among the mite species. It has been heavily exposed to acaricides among the acari and had developed resistance to dicofol, amitraz, organotins, propargite, pyrethroids, fenbutatin oxide, hexythiazox, clofentezine, abamectin and METI (Mitochondrial Electron Transport Inhibitors) acaricides fenazaquin, fenpyroximate, pyridaben and tebufenpyrad around the globe. The compilation and subsequent comparison of resistance data reported for different strains world wide is a complicated task because of the difference in bioassay methodology adopted, variation in the susceptibility of reference strains used to calculate the resistance ratio and stage of the mite (adult female/larvae) assayed for by the toxicologists. The establishment of baseline LC50 to new acaricides before widespread use may allow better monitoring of changes in susceptibility over time and can provide opportunity to detect resistance before the occurrence of field failure. Discriminating concentrations need to be determined for quick and reliable monitoring of resistance in the future. Genetically established resistance mechanisms in spider mites were similar to those found in insects (reduced penetration, target site insensitivity and enhanced metabolism). An ARM (Acaricide Resistance Management) package for T. urticae need to be developed that may guide for the mitigation of resistance. The magnitude of resistance and the mechanisms responsible for the acaricide resistance in T. urticae around the globe have been reviewed.
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