Browsing by Author "Baby P Skaria"

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Contact toxicity of different insecticides to third and fifth instar nymphs of brown plant hopper Nilaparvata lugens stal (Delphacidae : Homoptera)
(Kerala Agricultural University, 1981) Baby P Skaria; Das, N M
The relative efficacy of 1 2 contact insecticides to the third and fifth instar nymphs of the brown plant-hopper Nilaparvata lugens was assessed in the laboratory by assessing their LC 50 values. These chemicals were found to be equally effective against both the stages of the pest. Insecticides found most effective were carbaryl, monocrotophos, quinalphos, fenthion, phosalone, fenitrothion and dichlorvos. On relative cost basis these may be ranked ascarbaryl, monocrotophos dichlorvos, phosolone, fenthion, fenitrothion and quinalphos, against third instar nymphs and carbaryl, monocrotophos, quinalphos, fenitrothton, fenthion, phosalone and dichlorvos against fifth instar nymphs.
Infestation reactions and management of Helopeltis theivora (Waterhouse) (Miridae:Hemiptera) in cocoa clones
(Department of Entomology, College of Horticulture, Vellanikkara, 1998) Beena Nair; Baby P Skaria
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.
Resurgence potential of the rice leaf folder. Cnaphalocrocis.medinalis Guen. as influenced by the soil application of carbofuran granules
(Department of Agricultural Entomology , College of Horticulture, Vellanikkara, 1991) Baby P Skaria; Abraham, C C
In investigations on the changes taking place in the extent of feeding, growth and development of the rice leaf folder, Cnaphalocrocis medinalis Guen. on rice plants receiving soil application of carbofuran granules at 0.50, 0.75 and 1.00 kg ai/ha/application at 20, 50 and 20 and 50 days after transplanting, the extent of larval feeding on leaves did not show any variations as a result of carbofuran treatments. In the third, fourth and fifth larval instars and pupae, carbofuran treatments led to their weight gain due to possible enhancement of the digestibility and more effective conversion of ingested food into body matter, under .influence of factors mediated by the metabolites of carbofuran in leaf tissues. In respect of mean larval and pupal mortality, the insecticidal treatments did not show any impact, but the metabolites showed a negative correlation with the mortality levels thereby indicating the favourable influence of the metabolites on the development of C. medinalis. There was improvement in female emergence as a result of treatment with 1.00 kg ai/ha of carbofuran applied at 20 as well as 50 DAT as compared to untreated control, but the sex-ratio variations as a result of treatments were not pronounced. The first instar larval emergence (F1 generation) showed a positive influence by different metabolites of carbofuran. Carbofuran treated plants showed distinctly positive orientational stimulus to C. medinalis adults due to positive olfactory stimuli probably due to emission of vapour-phase admixture of carbofuran metabolites, but there was no improvement in fecundity under such treatments. There was distinct improvement in progeny production from females developing from carbofuran treated rice plants. This is mainly due to the ingress of more female moths and the resultant increase in overall ovipositional output rather than increase in fecundity'. Carbofuran treatments caused increase in the density of leaf hairs in a dose-dependent manner, but such variations were not significant as compared to untreated control. The positive relationship between ovipositional preference on the one hand and leaf hair density of treated plants .on the other brings to focus the role of tactile stimuli provided by leaf hairs in the acceptance of host plants for oviposition. The residues and metabolites of carbofuran in leaves favourably influenced most of the growth and developmental attributes of the rice leaf folder. None of the plant biochemicals showed any changes under influence of carbofuran treatments.