PhD Thesis

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Bionomics of pareuchaetes pseudoinsulata rego barros (lepidoptera:arctiidae) and its interaction with the siam weed chromolaena odorata king and robinson (asteraceae)
(Department of Agricultural Entomology, College of Horticulture, Vellanikkara, 1993) Lyla, K R; Abraham, C C
Studies were undertaken on the biology, morphometrics, feeding habits, factors affecting fecundity and fertility of Pareuchaetes pseudoinsulata King and Robinson (Arctiidae : Lepidoptera) and also the plant response of the weed host Chromolaena odorata L. at the College of Horticulture, Vellanikkara during 1990 – 1993. The morphometrics and morphology of the various immature stages and adults have been described. The total life-cycle of P. pseudoinsulata took a total of 46.75 days and the various developmental stages lasted for 5.5 days in eggs, 21.30 days for larvae (seven instars) 1.5 days for pre-pupa and 10.15 days for pupae at a mean ambient temperature of 28.40 C. In feeding trials to assess the relative preference of tender, mature, semi yellow and yellow leaves of C. odorata, it was found that the I instar larvae showed district preference to tender leaves as compared to mature leaves. The I and II instar larvae did not feed on semi-yellow and yellow leaves and they died of starvation when these types of leaves were offered for feeding. Consumption indices decreased as the age of larvae advanced and thus early instars consuming all the types of leaves recorded high indices. The rate of increase in larval weight gain was higher in later instars (VI and VII). Caterpillars feeding on mature, semi-yellow and yellow leaves showed higher Relative Growth Rate during IV to V stage, but during I to II stage, a high RGR was seen on larvae which fed tender leaves. Yellow. leaf diet for late instar larvae adversely affected their development and adult emergence. Highest fecundity was recorded when the parental sex-ratio of moths was kept at 1:1 level followed by 1:2 ratio and 2:1 in that order. Egg production and viability were significantly higher at 250 C and 75 per cent RH as compared to 300 C and 60 per cent RH. Adult food did not show any influence on fecundity but in respect of improvement of egg viability the treatments were advantageous. Total nitrogen content in leaves was maximum on the sixth day of release of four larvae per cage. Leaf nitrogen showed a declining trend when the larval load per plant was increased from the eighth day of release onwards. Soluble nitrogen content in leaves showed an increasing trend with increase in larval load per plant, but this however failed to reach significant levels. Chlorophyll content in leaves got reduced significantly at increased larval population loads and with passage of time of confinement. The natural enemies of P. pseudoinsulata consisted of avian fauna, spiders and ants and parasitoids. Predatory species of ants recorded in association with the insect included Lioponera sp. Oecophylla smaragdina Fabr. Solenopsis sp.and Monomorium sp. Occasionally NPV infection occurred in the laboratory as well as in field cultures causing substantial mortality. The implications of the various findings in reorienting the biocontrol strategies involving P. pseudoinsulata against C. odorata have been discussed.
Effect of sub-lethal doses of decamethrin and carbaryl on the orientation, feeding reproductive rate and survival of key pests of brinjal, Solanum melongena L.
(Department of Agricultural Entomology, College of Horticulture, Vellanikkara, 1989) Sheila, M K; Abraham, C C
The effect of sub-lethal doses of decamethrin and carbaryl at their LD5, LD10, LD25 and LD50 levels on orientational stimuli, feeding, reproductive potential and survival of the three important pests of brinjal, namely, the epilachna beetle H.28 punctata, the aphidsA. gossypii and the leaf hopper A. b. bicuttula have been studied in the laboratory. In all the three test insects, positive orientational stimuli were not detected at all the tested sub-lethal levels of the two insecticides. A decrease feeding rate in H. 28 punctata was detected when the insects were exposed to the sub-lethal dose treatments. In A. crossypii and A. b. biguttula, the reduction in the feeding rate was more pronounced at the LD 50 level of both insecticides.
Exploration of the feasibility of developing races of trichograma Australicum girault ( trichogramatidar, hymenoptera) suitable for different environments
(Division of entomology ,Agricultural college and research institute ,Vellayani., 1970) Abraham, C C; Pradhan, S
Host resistance in brinjal varieties to the fruits and shoot borer Leucinodes orbonalis Guen ( Lepidoptera: pyralidae)
(Department of Agricultural Entomology, College of Horticulture, Vellanikkara, 1983) Madhavan Nair, G; Abraham, C C
In studies on the host plant resistance in brinjal (Solanum melongena L.) against the shoot and fruit borer, Leucinodes orbonalis Guen. (Lepidoptera : Pyralidae), germplasm materials were screened to identify sources of resistance and an attempt was made to investigate the mechanisms of resistance involved. Forty accessions of brinjal and related species were initially screened in a field trial conducted during the monsoon season of 1982 and these were classified into highly susceptible, moderately susceptible, moderately resistant and resistant classes. The accessions SM-6, SM-56, SM-72 and SM-74 from the highly susceptible group; SM-1, SM-45, SM-48 and SM-71 from in moderately susceptible group; SM-65, SM-68, SM-97 and SM-105 from the moderately resistant group and SM-67, SM-88, S.indicum and S.incanum from the resistant group were further field tested during the summer season, 1982-83 and were evaluated for the levels of resistance. Under artificial infestation of caged single plants of the accessions by the first instar larvae of L. orbonalis, the susceptibility spectrum was found to be similar to the trend noticed in the field trials. In the resistant types, the infestation by L. orbonalis occurred for a relatively shorter duration than in the susceptible ones. In studies on the antibiosis, it was found that the resistant accessions gave rise to larvae and pupae of reduced weights which took longer durations as compared to the highly susceptible accessions. The larval survival was lower in the resistant types. The highly susceptible accessions produced more females than did the resistant line. There was no significant variation in the fecundity of second generation females. In multiple-choice and no-choice tests, the females of L.orbonalis showed a clear preference for the highly susceptible and moderately susceptible accessions for oviposition. Correlation studies revealed that the density of trichomes on the shoot apex, lower leaf surface and lower surface of midribs exerted considerable influence on the ovipositional response of the female moth, the relationship between oviposition and trichome density being of a negative nature. Among the biophysical characters, the higher density of trichomes on shoot apex and lower midrid; lower pith area, lingnified selerenchymatous hypodermis and compact vascular bundles in shoot apex and tight or semi-tight calyx in fruit were found to impart resistance to borer infestation. Positive correlations were detected between the mean percentages of total sugars, crude protein, total ash, nitrogen, potassium and calcium in the fruit on the one hand and fruit infestation on the other. The contents of total ash, calcium, magnesium and iron in shoots on the one hand and shoot infestation on the other were also found to be positively correlated, while silica, zinc, copper and crude fibre contents were negatively correlated with shoot infestation.The implications of the findings have been discussed.
Host-specificity, patho-physiology and transmission of the baculovirus (Kerala isolate) infecting Oryctes rhinoceros Linn. (Scarabaeidae:Coleoptera)
(Department of Agricultural Entomology, College of Horticulture, Vellanikkara, 1995) Suma Paulose; Abraham, C C
The Baculovirus oryctes has been recognized as one of the most promising pathogens against oryctes rhinoceros. Laboratory studies were conducted to evaluate the virus in respect of its patho-physiology, histopathology, mode of transmission, cross-infectivity, effect of physical factors on the virulence of the virus and safety to non –target organisms. The oral inoculation technique has been found to be more effective than the swim method. For long term storage of the virus, the freeze drying method was found to be ideal as it retained viability for more than sixteen months. The viral particles have been found to be bacilliform , measuring 210 to 250nm in length and 75 to 105 nm in width. The main symptoms observed in grubs due to viral infection are loss of appetite, lethargy, pallor, migration to the top of the breeding medium, disintegration of the fat bodies and development of diarrhoea. Adults did not show any pronounced external symptoms. Infected adults refused to take food and they eventually developed diarrhea. All instars of grubs and adults were susceptible to the viral infection .The susceptibility to infection was maximum in the first instar followed by third instar, second instar and the adults in that order. The mean lethal concentration of the viru required to cause fifty per cent mortalities were 0.377 x10-4 , 14.417x10-4, 0.297x10-4 and 1.137x10-4 gut equivalent for the first, second and third instar grubs and adults respectively. The cytology of the midgut contents showed desquamated epithelial cells with nuclear and cytoplasmic vacuolation, nuclear hypertrophy and ring stages nucleus. The midgut and fat bodies have been identified as the major sites of viral multiplication. Transovum and transovarial transmission studies have shown that the virus was not transmitted by any of these method. The studies on transtadial transmission established that the disease was transmitted from first to second and from second to third instar, but not from the third instar to the pupae. The predator platymerus laevicollis did not transmit the disease. The reproductive potential of oryctes was found to be significantly impaired due to viral infection. When both the mating partners were infected, the number of eggs laid was only 19 to 20 as compared to the output of 209 to 219 in the healthy pairs. The cross-infectivity studies have clearly established that the virus was not infective to other important pests of coconut such as Rhyncophorus ferrugineus, Leucopholis coneophora, opisina arenosella and the predator’s p.laevicollis. In studies on the effect of temperature on the viability of the virus, it was found that above fifty per cent mortality took place on incubation of the virus for 21/2 hours at 370c and that the viability was totally lost as a result of exposure for 4 1/2 hours. The number of adults required for release in to the breeding pits of size of 30cmx30cmx30cm to kill fifty per cent of the Rhinoceros grubs at different time intervals were 4.440, 3.668, 3.016 and 2.889. Safety studies have revealed that the virus was absolutely safe to the silkworm Bombyx mori, chick embryo, white mice and white rat.
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.