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Subject: Agricultural Entomology × End date: 1991 × Start date: 1991 × Type: Thesis × Thesis Type: M.Sc ×
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    ThesisItemOpen Access
    Effect of chitin synthesis inhibitors on rice swarming caterpillar spodoptera mauritia and rice moth corcyra cephalonica and a larval parasitoid bracon brevicornis
    (Department of Agricultural Entomology, College of Agriculture, Vellayani, 1991) Prathapan, K D; KAU; Dale, D
    Effects of four chitin synthesis inhibitors viz. diflubenzuron, chlorfluazuron, PH 70-23 and BASF LAB 153 959 I were assessed on two insect pests, the rice swarming caterpillar Spodoptera mauritia ( Boisduval) and rice moth Corcyra cephalonica (Stainton) and on its larval parasitoid Bracon brevicornis (Wesmael). Ovicidal action was assessed by treating one and two-day old eggs of S. mauritia in aqueous and mathanilic media. It was low in aqueous medium. But in methanolic medium diflubenzuron and the highest doses of the other three compounds showed enhanced action. In general, high ovicidal action was observed in methanolic medium. There was no significant difference between one and two-day old eggs in their susceptibility to chitin synthesis inhibitors. Chlorfluazuron was the most toxic causing cent per cent mortality at doses as low as 2 x 10 -5% when treated on second and fifth instar larvae of S. mauritia. Diflubenzuron, PH 70-23 and BASF LAB 153 959 I were also highly effective. Second instar larvae were more susceptible than fifth instar ones. Besides stomach action, a high degree of contact action was also observed. Final instar larvae of S. mauritia when treated with the test chemicals, produced larval-pupal intermediates and caused pupal mortality and emergence of deformed adults. All the four moult inhibitors were highly active during larval – pupal transformations. Pupae were less susceptible to chitin synthesis inhibitors. Yet, some treatments caused mortality and emergence of deformed adults. Chlorfluazuron was the most toxic to pupae. Fecundity, hatchability of eggs and longevity were reduced when the male moths of S. mauritia were fed on sugar solution containing the moult inhibitors. Antifeedant action of the chitin synthesis inhibitors was found to be less pronounced. Residual effect of all the four compounds persisted on the treated rice foliage throughout a study period of 36 days. But the efficacy of residues exposed to sunlight and rain was very low. Ovicidal action of the moult inhibitors was low to moderate on one and four-day old eggs of C. cephalonica in aqueous medium. In methanolic medium diflubenzuron at 2 x 10 -1 %, 2 x 10 -2 % and 2 x 10 -3 % and PH 70-23 and BASF LAB 153 959 I at 2 x 10 -1 % caused enhanced ovicidal action. In general there was no significant difference between the susceptibility of one and four-day old eggs. Chlorfluazuron was found to be the most toxic compound against larvae of C. cephalonica followed by BASF LAB 153 959 I. Diflubenzuron and PH 70-23 were less effective. Early larval instars were more susceptible. Contact action of compounds other than chlorfluazuron was low. Larval – pupal intermediates, pupal mortality and emergence of deformed adults were resulted when the last instar larvae of C. cephalonica were treated with the chemicals. Chlorfluazuron was found to be the most toxic compound. Prepupal treatment also caused the above juvenomimetic effects. But treatments other than chlorfluazuron 2 x 10 – 2% were less effective. Treatment of pupae of C. cephalonica resulted in pupal mortality and emergence of deformed adults. But pupae were less susceptible to the moult inhibitors as compared to the larval stages. External application of Chitin synthesis inhibitors to moths of C. cephalonica had no adverse had no adverse effect on fecundity, hatchability of eggs and longevity of the treated moths. Chlorfluazuron was found to inhibit the emergence of adult parasites from treated hosts and adversely affect the progeny production of B. brevicornis. Diflubenzuron, PH 70-23 and BASF LAB 153 959 I were non-toxic or only slightly toxic to the parasite.
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    ThesisItemOpen Access
    Nematodes associated with the tuber crops In Kerala
    (Department of Agricultural Entomology, College of Agriculture, Vellayani, 1991) Remesh, Kumar V; Ravindaran, Nair K K
    A survey of plant parasitic nematodes of tuber crops, cassava, sweet potato, coleus, colocasia/xanthosoma and diascorea in twenty five panchayats representing five agroclimatic zones of Kerala was conducted during December, 1988. This was the first attempt in this line of investigation. Meloidogyne sp. and Rotylenchulus sp. were more widespread with all the five tuber crops in the five agroclimatic zones of Kerala. These two genera were seen in soil and root samples. Rotylenchulus sp. was more predominant than Meloidogyne sp. in tapioca, sweet potato and diascorea than in colocasia /xanthoma and coleus. The two genera of nematodes are potential threat to cultivation of all the five tuber crops in Kerala. Pratylenchus sp. was also observed in soil samples associated with all crops but it could be collected from the root samples of diascorea and colocasia/xanthosoma only. In high population the genera may become a potent meance to both the crops since its pathogenecity on these crops have already been established. Helicotylenchus sp. and Radopholus sp. could be seen in soil samples associated with all the crops, Helicotylenchus sp. was more predominant in distribution and intensity in the tuber crops in all the agroclimatic zones. Hoplolaimus sp. was seen associated with diascorea alone in soil samples among the five crops in most cases. Tylenchorynchus sp. could be obtained from soil samples associated with all crops except diascorea. Heterodera sp. and Tylenchus sp. were recorded from colocasia/xanthosoma and sweet potato very sparsely. The effect of varying levels of M. incognita on the growth parameters and yield of C. esculenta was assessed in a pot culture experiment. A population of 500 larvae per plant found causing 12 per cent yield reduction over control. With an increase in the initial population of the pest a progressive suppression in plant height, number of leaves, shoot weight, root weight and weight of tubers and an increase in trend in pest population, root knot and percentage of galls (weight basis) were observed. But these were not linear. Apparently healthy tubers harvested from the nematode inoculated treatments suffered spoilage in storage. Histopathological observation of M. incognita infested colocasia roots showed that the damage was similar to those reported in colocasia roots showed that the damage was similar to those reported in coleus and sweet potato. A pot culture experiment revealed that the extent of adverse effect on the tuber crops did not show wide variations at the normal and water stress conditions. In coleus the adverse effect on the growth of the plant by nematodes was more with higher levels of irrigation. Less frequent irrigation in sweet potato and coleus caused higher reduction in the population of the pests compared to that in dioscorea. Even with lesser population of nematodes more damage can occur in a crop under stress and the response was found to vary with crops.