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19993
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Subject: Agricultural Entomology × End date: 1999 × Start date: 1999 × Thesis Type: M.Sc ×
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    ThesisItemOpen Access
    Resistance mechanisms against the pseudostem weevil odoiporus longicollis olivier (coleoptera : curculionidae) in banana
    (Department of Agricultural Entomology, College of Horticulture, Vellanikkara, 1999) Lalitha, N; KAU; Ranjith, A M
    The present investigation on resistance mechanisms against pseudostem weevil Odoiporus longicollis Olivier (Coleoptera:Curculionidae) in banana was undertaken in the Department of Entomology, College of Horticulture, Vellanikkara during 1997-99. In insect-plant interactions, it is always the survival of the fittest. There is also a constant enhancement in the physiological preparedness both by the insect and the host plant to gain the upper hand. It is felt that even though the insect conqu6¥$ the resistance of the host plant in majority of cases, there may be a threshold of insect attack, which would induce plant defenses to deter the attack. It was also possible that some of these plant defenses may be triggered off by enzymes produced in the plant system consequent to the attack. These incitory enzymes or chemicals may be transferred to the offspring, which would make them resistant to attack, by the weevil. Hence, major objectives of the study were to evaluate sucker and in vitro regenerated progenies of infested Nendran (AA B) for resistance against 0. longicollis, to evolve methods for screening resistance under artificial conditions, laboratory rearing of 0. longicollis and identification of morphological, biochemical and anatomical bases of resistance using Nendran as susceptible and Njalipoovan as the resistant source. Preliminary field screening of Musa (AAB) Nendran for resistance against pseudostem weevil was done based on the number of ovipunctures/feeding holes on the pseudostem, surface area of infestation and the size of feeding holes. All of these contributed to the intensity of the attack. The multiplication product of these factors led to the development of a new 0-4 rating scale, for scoring the damage by 0. longicollis in the field. No-choice tests conducted on sucker and in vitro regenerated progenies of such graded mother plants revealed a better performance by plants having lower history of infestation. This suggested the existence of induced resistance involving triggering off of enzymatic reactions. Besides these lower grades, the plantlets of G4 exhibited better tolerance than control by exerting greater potential to stand amidst heavy winds till complete maturity of the bunch. The in vitro regenerated plants performed much better than the sucker derived treatment plants. This offers potential for mass multiplication of such in borne resistance for commercial release. The results obtained so far opens up the possibility of induced resistance that may be genetically inherited to the plantlets from its mother as an evolutionary character. Such triggering mechanism operating in vivo offers greater potential to select resistant clones. The methodology for screening banana for resistance to 0. longicollis by artificial infestation in field situations was standardized. Four adult weevils in the sex ratio 1: 1 (2!f' and 2 r:J) was found to be optimum to create moderate levels of infestation during the most favourable season (May-August). Mass rearing of 0. longicollis in laboratory conditions using natural diet was quite successful for maintaining a large-scale population throughout the year. A continuous supply of uniformly aged test insects for exposing the experimental plants at specific pest load was made possible by this. Studies involving the duration of development of the weevil revealed acute antibiosis in Njalipoovan manifested by reduced egg laying prolonged duration of life cycle, reduced hatching of eggs (39.5%) and reduced adult emergence from eggs (29.7%) in contrast to 94.9 per cent hatching of eggs and 9l.3 per cent adult emergence in Nendran. A no-choice test was designed to study the appropriate age of Nendran from which it becomes susceptible to infestation. Results indicated a distinct preference for oviposition by the adults on pseudostem of banana from seventh month onwards. This information helps to reduce the insecticidal load in the banana ecosystem by advocating pesticides from seventh month only. The existence of oviposition deterrency when more females were confined to Nendran pseudostem pieces revealed the deposition of spacing pheromones by conspecific females after egg laying. It was seen that the acetone and ether extracts of pseudostem pieces where ten females had laid their eggs, when sprayed on fresh pseudostem, deterred the oviposition by other females. Isolation and identification of such epidectic compounds will help in their utilisation in the field to prevent egg laying on banana pseudostem. The morphological, anatomical and biochemical bases of resistance were also identified. The morphological parameters associated with resistance were smaller width and breadth of the sheath coupled with more number of sheaths in the resistant variety. These increased the number of cuticular layers and cell walls the grub had to traverse before entering the central pith. The pith formation is of prime importance to the curculionid as it becomes the target site of feeding for third and fourth in stars. There are certain cues emanating from the pseudostem subsequent to maturity, which aids the adult weevils in host selection and oviposition. The lesser moisture and higher crude fibre content of Njalipoovan pseudostem exhibited greater influence on resistance by posing a mechanical barrier to egg laying and feeding of neonate larva. The information on moisture content is of practical utility in the management of the pest in endemic areas. It may be possible to artificially create moisture stress in the plant attaining flower bud initiation stage by regulating irrigation. The level of irrigation has to be adjusted so as not to induce a yield reduction but at the same time to induce moisture stress at least in the outer sheaths to prevent oviposition. The water suckers served as more conducive hosts for the pest even before sufficient maturity and this highlighted the need for removal of water suckers from endemic fields. The anatomical sections of pseudostem sheath clearly revealed a thick cuticle on epidermal cells with four to five layers of dense collenchymatous hypodermis imposing a physical barrier against oviposition in the resistant cultivar. Further, the ground tissues which constituted of compactly arranged parenchymatous cells with several starch grains offered feeding deterrency. The closely packed bigger sized lower epidermal cells along with additional parenchymal layers below the air cavity operated as a mechanical barrier which caused the failure of the neonate larva to penetrate inner tissues. Higher content of phenolics generally showed a positive correlation with resistance. However, the role of ortho dihydric phenolic substrates in resistance is greatly dependent on the enzymatic activity of polyphenol oxidase to form toxic metabolites like quinones and tannins. Hence, the oxidation factor of OD phenols clearly indicated the dominance of the resistant variety, Njalipoovan. The accelerated activity in Njalipoovan is endowed with greater potentiality to activate polyphenol aggressively effecting more production of lignin, quinone and tannins, in the event of egg laying or feeding by the pseudostem weevil.
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    ThesisItemOpen Access
    Eco-friendly management of important sucking pests of chilli
    (Department of Agricultural Entomology, College of Agriculture, Vellayani, 1999) Santhosh Kumar, T; KAU; Reghunath, P
    The experiment was conducted in the Instructional Farm, College of Agriculture, Vellayani during 1997-98. The results of the pot culture experiment for studying the symptoms developed by Aphids CA. gossypii) , Thrips (S. dorsalis) and mites (P. latus) revealed that P. latus were the most serious sucking pest than aphids and thrips in the combined release. The population build up of each pest were high when released alone, while in combined release the maximum build up was recorded by mites The most prominent symptoms developed by aphids were yellowing of older leaves and reduction in the size of tender leaves and shoots. The symptoms developed by thrips were cupping, upward rolling of leaf margins, reduction in the size of leaves, brittled leaves and finally the plants became stunted. While the noticeable symptoms of mites were, downward curling of leaves, elongation of leaves, inverted boat shaped leaves, silvery lining on the ventral surface of leaves and in advanced stages the leaves and tender portions of stem became hard and brittle and finally the plants became stunted. The results obtained in the feeding efficiency study of natural enerrues recorded the efficient feeding of spiders and coccinellids on aphids. On thrips spiders were fed efficiently while coccinellids did not feed on thrips. Regarding the field experiment for the evaluation of insecticides, acaricides and botanicals and their combinations, the treatment plant extract of 1 101 A. paniculata with garlic (l 0 %) gave good control of aphids, thrips and mites resulted in maximum yield as compared to other treatments. The population build up of natural enemies was also maximum in this treatment. Neem seed oil emulsion at 10 per cent concentration was also foune! to give good control of sucking pests. Among the chemicals tested monocrotophos 0.05 per cent and malathion 0.2 per cent gave good control of three sucking pests. Regarding the combinations of bot anica Is with chemicals, neem seed oil emulsion with each one of the three chemicals gave promising results.
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    ThesisItemOpen Access
    Trapping of red palm weevil in coconut gardens
    (Department of Agricultural Entomology, College of Horticulture, Vellanikkara, 1999) Ramesha, B; KAU; Jim, Thomas
    Experiments were undertaken in the Department of Agricultural Entomology, College of Horticulture, Vellanik:kara during 1997-1998 to evaluate the efficacy of the male aggregation pheromone Ferrolure (4-Methyl-5 nonanol) in mass trapping the redpalm weevil of coconut Rhynchophorus ferrugineus F (Oliv.) in the coconut plantations of Thrissur district. A survey was conducted in Thrissur district in three regions representing three geographical zones viz., coconut plantations in coastal zones, midland regions and upland conditions with the respective red palm weevil damage incidence of 5.33 per cent, 7.66 per cent and five per cent with an average incidence of six per cent. A convenient and suitable bucket trap was designed and fabricated for the mass trapping of the adult weevils from the field and for further laboratory experiments. Out of the different food attractants tried pineapple waste and toddy gave increased trapping efficiency of the weevils with the pheromone sachet. The food attractants was necessarily to be renewed afresh once in three to four days interval so as to keep the trap effective. At this rate of change of the food attractant a single pheromone sachet was found to be actively performing to trap the weevils for a period of 10-12 weeks. The Ferrolure tried was found to be predominently a male aggregation pheromone but with reasonable attraction to female weevils as well. The best exposure height of the pheromone trap was at a height range of one to two meters from the ground level within the coconut plantations to offer maximum trapping efficiency.' An DV light source at night was found to supplement the weevil trapping along with the pheromone trap giving 2.85 times more catch. In conclusion the experimental observation proves the overall efficacy of the ferrolure with pineapple as a food attractant coupled with the bucket trapping device. If the traps are installed at one to two meter above the ground level in the plantation, this gives good performance in trapping the male and female adult weevils for an effective period of nine to 10 weeks. A large number of weevils could be trapped which will probably reduce the damage of this weevil below the existing six per cent of damage. Food substance should be changed periodically at an interval offour days to retain the efficiency.