PhD Thesis

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Subject: search.filters.subject.Agricultural entomology

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    Morphological and molecular characterization of eastern honey bee (Apis cerana Fabricius) in Kerala
    (Department of Agricultural Entomology, College of Agriculture, Vellayani, 2023-06-09) Chinchu P Babu.; Amritha V S
    An investigation on “Morphological and molecular characterization of eastern honey bee (Apis cerana Fabricius) in Kerala” was carried out at the Department of Entomology, College of Agriculture, Vellayani during 2017-2022 with the objective to identify the morphological and genetic diversity of eastern honey bee (Apis cerana Fabricus) in southern, central and northern zones of Kerala. Survey was conducted in three zones of Kerala viz., southern, central and northern zones. Twenty worker bees each were collected from 75 colonies (feral /natural colonies as well as managed/ domesticated hives) of twenty five localities representing each zone. The nesting habitat, nesting site, nest height and nest characteristics of honey bee colonies from forest areas in Kerala were examined. Feral colonies of cavity nesting honey bees were found to inhabit the primary forests, disturbed and undisturbed lands as well as agricultural lands in Kerala. Tree hollows, rock crevices, mud wall, termite mound, letter box and mud pot were the nesting sites of cavity nesting bees in Kerala and majority of the bees were found to occur at a nest height of 0 cm to 200 cm. The number of combs in the colony varied from five to twelve. An exploration of foraging sources of honey bees in forest areas were done for the first time in Kerala via metabarcoding of rbcL (ribulose- bisphosphate carboxylase) gene. Plants belonging to 256 genera were identified as foraging sources of honey bees in forest areas of Kerala with Gossypium as the abundant genus in southern zone, Elaeis in central zone and Drypetes in northern zone. Seventeen genera of plants were common in all the three zones of Kerala i.e. Pterocarpus, Cannabis, Prunus, Ceiba, Ulex, Galatella, Myosotidium, Vachellia, Valeriana, Cassia, Androsace, Senna, Luisia, Cocos, Peliosanthes, Esmeralda, and Parkia among which Pterocarpus, Cannabis, Prunus, and Ceiba were the prevalent genera as the foraging source of honey bees in forest areas of Kerala. As part of the morphological studies, five worker bees from each colony were dissected and subjected to standard morphometric analysis using 29 parameters. No significant differences were observed in most of the morphological parameters among the zones. Based on elevation, the populations were classified as ‘Plain’ (<300 m above MSL) and ‘Hill’ (>300m above MSL) populations and ‘t test’ analysis among the populations showed highly significant differences across most of the size related morphometric characters viz., ratio of head length and width (HLW), distance between ocelli (DBO), ocello-ocular distance (OOD), proboscis length (PL), antennal length (AL), ratio of length and width of fore wing (FWLW), cubital index (CI), wing angles (A 32, A 38), length of third tergite (3TEL) and length of fourth tergite (4 TEL) and ratio of length and width of wax plate (WPLW). Moreover, the ‘Hill’ populations of honey bees exhibited higher values for most of the size related as well as wing related characters. Factor analysis yielded six factors with Eigen value > 1. The major factor (F1) was derived from honey bee size related characters (HLW, PL, AL, CI, 3TEL, 4TEL and WPLW) with high factor loadings in between 0.66 to 0.92 accounting for 35 per cent of the variation among the samples. Hence, these characters were found to be the main indices that could be used to discriminate among the populations. The hierarchical cluster analysis (HCA) of 75 populations with 29 morphological characters revealed the presence of two main clusters, ‘Plain’ group cluster and ‘Hill’ group cluster, the same being confirmed in linear discriminant analysis (LDA). The correlation analysis of morphological traits with elevation revealed that proboscis length (PL), antennal length (AL), cubital index (CI), ratio of head length and width (HLW), ratio of length and width of wax plate (WPLW), length of third tergite (3 TEL) and length of fourth tergite (4 TEL) exhibited positive linear correlation with topographic elevation. The ‘Hill’ and ‘Plain’ populations of honey bees exhibited variations in the colour and pigmentation pattern of different morphological traits viz., second tergite, third tergite, third sternite and abdomen. The everted endophallus of honey bee drones showed variations in the vestibulum, cervix and bulb indicating reproductive isolation between ‘Plain’ and ‘Hill’ populations of cavity nesting bees in Kerala. Surface pattern of bulb and vestibulum were detected through scanning electron microscopy (SEM) imaging wherein they exhibited variations in the surface structures. Molecular characterization of 75 populations of cavity nesting bees in Kerala was also carried out by amplifying the mitochondrial cytochrome oxidase I (COX I) gene. Phylogenetic analysis of the 75 bee populations from Kerala using maximum likelihood method identified the ‘Plain’ group as A. indica Fabricus, 1798 and the ‘Hill’ group as A. cerana Fabricus, 1793. Haplotype analysis of the populations revealed the existence of fifteen COX I haplotypes in Kerala, out of which fourteen were new haplotypes. Pair wise genetic distance of the samples revealed high nucleotide divergence (5.1% - 7.0%) between A. indica and A. cerana. The network analysis of haplotypes also supports the divergence between A. indica and A. cerana in Kerala. These fifteen nucleotide sequences of the haplotypes were submitted to NCBI Genbank and BOLD. Comparative metagenomic analysis of gut microbiome of A. indica and A. cerana revealed variations in the abundance of gut microbiome between the two species. The abundant genus recorded in A. indica was Lactobacillus while in A. cerana Gilliamella was the prominent genus. Morphological and molecular analysis of 75 populations from Southern, Central and Northern zones revealed the existence of two discrete populations of cavity nesting honey bees in Kerala i.e. ‘Plain’ population and ‘Hill’ population. Significant variations in the morphometric parameters of the bee populations were observed at elevations rather than the zones. Studies on the external genitalia revealed reproductive isolation between ‘Plain’ and ‘Hill’ populations of cavity nesting bees in Kerala. Haplotype analysis revealed fifteen COX I haplotypes of cavity nesting bees in Kerala, wherein fourteen haplotypes were new from Kerala. Thus, the present study revealed the existence of two species of cavity nesting bees in Kerala i.e. the Plain group, A. indica and Hill group, A. cerana.
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    Bioecology of major coccinellid predators of Kerala
    (Department of agricultural entomology, college of agriculture , Vellayani, 2023-07-07) Anusree, S S; Anitha, N
    An investigation on “Bioecology of major coccinellid predators of Kerala” was carried out at Department of Entomology, College of Agriculture, Vellayani during 2017-2022 with the objective to identify major coccinellid predators of pests infesting agricultural crops from agro ecological zones of Kerala and to study biology and predatory potential of select coccinellids. In the present investigation, 40 species of predatory coccinellids belonging to 23 genera under 6 tribes in the Subfamily Coccinellinae were illustrated. Taxonomic study on tribes Aspidimerini and Chilocorini resulted in the identification of three species in each tribe. Examination on specimens of tribe Coccidulini resulted in identifying 16 species within five genera. 11 species belonging to nine genera were illustrated under tribe Coccinellini. A single species was illustrated and studied under tribe Hyperaspidini. The specimens studied under tribe Sticholotidini belonged to six species within four genera. Among the 40 illustrated species, 28 species were identified, while identity of 12 species are to be confirmed, of which three are putative new species. Phrynocaria perfida Poorani collected and illustrated during this investigation were confirmed and described as a new species (Poorani et al., 2021). Chilocorus sp.1 and Scymnus (Pullus) sp.4 are the other two putative new species. Phrynocaria perrotetti (Mulsant), Cryptogonus orbiculus (Gyllenhal) and Sticholotis ferruginea (Gorham) are new records from Kerala.
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    Microbial formulations for the management of spodoptera litura F.
    (Department of agricultural entomology, college of agriculture , Vellayani, 2023-06-30) Hari Sanker S S.; Faizal, M H
    The present study entitled “Microbial formulations for the management of Spodoptera litura F.” was conducted in the Department of Agricultural Entomology, College of Agriculture, Vellayani during 2018-2022 with an objective to develop ecofriendly, biologically based formulations comprising of entomopathogenic fungi (EPF) and nuclear polyhedrosis virus (NPV) in plant derived carrier materials for the management of the polyphagous pest S. litura.
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    Influence of weather and rearing techniques on mulberry silk worm crops in Kerala
    (Department of Agricultural Entomology, College of Agriculture, Vellayani, 1998) Krishnakumar, R; Sasidharan Pillai, K
    Investigations were conducted on the effect of weather parameters on the mulberry silkworm crops reared in different seasons and to evolve suitable rearing technology for stress seasons in order to improve the rearing during these seasons and for developing suitable package of practices recommendations for silkworm rearing in Kerala. The study was conducted during 1992-1996 at College of Agriculture, Vellayani. The experiments conducted were  Effect of climatic factors on mulberry silkworm crops in different seasons.  Identifying rearing technology for stress seasons of high temperature and humidity.  Manipulation of feeding schedule with reference to stress seasons and types of silkworm rearing houses. To study the effect of climatic conditions on the mulberry silkworm crop, the silkworms were reared during different identified seasons viz December- January, February-April, May-July, August-September and October-November in 1993-94. The mulberry silkworms used for the study were bivoltine NB4Dz and crossbreed PM x NB4D2. Three brushing were done in each season at fortnightly intervals and fifteen continuous rearings were conducted. The important weather parameters recorded were maximum temperature, minimum temperature, maximum humidity and minimum humidity inside and outside the rearing house. The rearing characters like instarwise larval duration, moulting duration, larval weight, leaf consumption, silk gland weight, disease incidences, missing larval percentage and economic traits like cocoon weight, shell weight, shell ratio, effective rearing rate, filament length, reelability and computed parameters like growth index and growth rate were also recorded. Among the different seasons, August-September and December-January were identified as the favourable seasons. October-November, February-April and May-July seasons were found to be the stress seasons as the biological and economic traits of the different silkworm races during these seasons were not compromising in comparison with other seasons. Maximum temperature and minimum temperature show direct correlations whereas maximum humidity indirectly showed negative correlations with the economic traits like larval weight, silkgland weight, shell ratio, cocoon weight and yield. Second and third experiments were conducted to identify suitable cost effective and efficient rearing house for these stress seasons and also to evolve rearing technology so as to reduce cost of production. The treatments for the second experiment were five different rearing houses along with three different larval spacings. The rearings were conducted by using the same crossbreed and bivoltine race used in the first experiment. The rearings were carried out during 1995 and 1996 in the three stress seasons viz May-July, October-November and February-March. The observations were recorded in terms of the larval characters and economic traits of the silkworms NB4D2 and PM x NB4D2 in these seasons. The results revealed that wider spacing was superior to medium and close spacings in both races. The rearing houses made of mud brick and thatched roof and burnt brick and thatched roof were found superior to other rearing houses in all the three stress seasons during the two year period. Among the different feeding schedules studied in the third experiment, three feeding a day was mostly on par with four feeding a day but was advantageous in terms of convenience of feeding time over other feeding schedules though four feedings recorded higher values for some biological and economic traits in the different silkworm types during different seasons. The incorporation of new techniques of rearing the crossbreed silkworm types in thatched mud wall rearing house, medium spacing of worms and three feeding a day was found to be an ideal profitable package during unfavourable seasons as comparable to that of favourable seasons.
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    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.