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Infestation Reactions and Management of Helopeltis theivora(Waterhouse) (Miridae:Hemiptera) in Cocoa Clones
Investigations were carried out at the College of Horticulture, Vellanikkara to identity sources of resistance to the cocoa mirid bug He/ope/lis theivora (Waterhouse) among the various high yielding cocoa clones and also to develop an effective and safer management strategy against the pest using...
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| Formato: | Ph.D Thesis |
| Idioma: | Undetermined |
| Publicado em: |
Vellanikkara
Department of Entomology, College of Horticulture
1998
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| 245 | |a Infestation Reactions and Management of Helopeltis theivora(Waterhouse) (Miridae:Hemiptera) in Cocoa Clones | ||
| 260 | |a Vellanikkara |b Department of Entomology, College of Horticulture |c 1998 | ||
| 502 | |b MSc | ||
| 520 | 3 | |a Investigations were carried out at the College of Horticulture, Vellanikkara to identity sources of resistance to the cocoa mirid bug He/ope/lis theivora (Waterhouse) among the various high yielding cocoa clones and also to develop an effective and safer management strategy against the pest using insecticides. In the field trial, seven hybrids and eight parental clones were evaluated for their tolerance to the mirids at different developmental stages of the pods and on flushes. The pod damage intensity was moderate to low, the range being 0.25 to 5.84 per cent and in this situation the resistance traits could not be properly quantified. However, the parental trees 01-5.9 and GYl-68 and the hybrids involving these trees showed a moderate level of resistance. The clones M-l3.12 and GI-15.5 were found to be relatively more susceptible to the pest. The correlation studies have established the positive correlation between the yield of pods on the one hand and the intensity of damage to the pods and the vegetative flushes on the other. The various pod characters such as length, width, weight, pericarp thickness, wet bean weight and number of beans per pod did not show any influence on the intensity of pod infestation. 'The performance of the various clones in respect of the yield of pods and beans have been discussed in the light of variations in the intensity of damage to the pods and vegetative flushes. The susceptibility of clones with higher number of pods was detected in the correlation studies. The hybrid GI-S.9 x GVI-68 which produced 23 pods per tree on an average showed lower levels of damage by the mirid bug on the pods and also on flushes indicating a moderate level of resistance coupled with high pod number in this clone. The pod number was also found correlated with total wet bean yield per tree, height and spread of the tree. With respect to higher wet bean yield the parental clone GYI-68 ranked first with 1937.47 g followed by M-13.12, GVI-64, GVI-6I, M-13.J2 x GJ-S.9 and GI-S.9 x GVI-68. The crosses GJ-IO.3 x GVI-61 and 01-5.9 x GVl-54 recorded very low bean yields. However, the high yielding and low yielding clones showed varied reactions to the infestation by H. theivora. With regard to the management of H. theivora using insecticides the spray application of carbaryl at 1.25 kg ai/ha and monocrotophos at 0.5 kg ai/ha was most effective. However, considering the higher persistent toxicity of monocrotophos, carbaryl is recommended for field applications. | |
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