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ThesisItem Open Access Food- web interaction and community structure of cabbage ecosystem(2020-01) Sarma, Daizy; Saikia, D. K.Field experiment were carried out in the Experimental Farm, Department of Horticulture, Assam Agricultural University, Jorhat during rabi 2017-18 and 2018-19 to study the food web interaction and community structure of cabbage ecosystem. Major insect pests recorded during both the crop season from 20 DAP, were cabbage aphid, Brevicoryne brassicae (L.), diamondback moth, Plutella xylostella (L.), cabbage butterfly, Pieris canidia (L.), cutworm, Agrotis ipsilon (Hfn.), cabbage looper Trichoplusia ni (Hubner) and flea beetle, Monolepta signata Oliv with minor pests viz., sawfly, Athalia proxima, cabbage head borer, Hellula undalis (L.), handmaiden moth , Syntomoides imaon (L.), epilachna beetle, Epilachna spp. (L.) and green stink bug, Nezara viridula (L) were also persisted on the crop right from the seedling stage to harvesting of the crop. Six numbers of predators viz., Coccinella transversalis (F.), Maenochilus sexmaculatus C. septempunctata (L.), Micraspis discolor (F), Harmonia dimidiata (F), Episyrphus belteotus (L.) and one number of predatory spider, Oxyopes spp. were recorded from cabbage ecosystem. In the present investigation, among different insect pests encountered in the field, B. brassicae showed the highest relative abundance ( 28.78%) on HYV and 29.65% for hybrid variety followed by A. ipsilon (20.45% for HYV and 17.65% on hybrid) during 2017-18 and same trend also found during 2018-19. Different weather parameters related to the correlation study indicated that the minimum temperature had negative significant impact with the population build up of B. brassicae (r= -0.652), P. canidia (r= -0.638), T. ni (r= -0.627) and M. signata (r= -0.596), whereas, BSSH showed positive significant effect with A. ipsilon (r= 0.620) in HYV variety. In case of hybrid variety, all major insect pests and predators showed negative significant effect with minimum temperature except T. ni during 2017-18. During 2018-19, a negative significant correlation was observed in between insect pests and predators associated to local and hybrid variety. The correlation of B. brassicae and coccinellid predators for both varieties showed a significant positive impact for 2017-18 and 2018-19. The different physiomorphic, biochemical parameters and the number of insect pests and predators for both the varieties were at par with each other during 2017-18 and 2018-19. Glucosinolate, phenol and Flavonoid content showed a negative association with major insect pests and predators for both the varieties during the investigation of 2017-19. The diversity study of insect pests in different phenological stages of cabbage indicated highest species diversity and evenness during the pre heading stage of cabbage followed by heading stage whereas, highest species richness was recorded during seedling stage for both the varieties during 2017-18 and 2018-19. In case of distribution pattern, a contagious distribution (both HYV and hybrid variety) was assessed for insect pests and their natural enemies during the present investigation. The consumption of aphids by C. transversalis, when applied individually and in different combination showed that highest consumption rate of 133.40±2.25 was observed in C. transversalis (Adult) x C. transversalis (Adult) followed by C. transversalis (Adult) x C. transversalis (4th) and C. transversalis (Adult)x C. transversalis (3rd ) with 104.90±2.25 and 99.10±2.25, respectively. In case of Consumption of aphids by M. sexmaculatus, highest result was observed in M. sexmaculatus (Adult) x M. sexmaculatus (Adult) combination with 96.26 ±3.60. Consumption of aphids when applied C. transversalis and M. sexmaculatus in different combination, highest consumption rate of 109.10 ± 2.37 was found in C. transversalis (Adult) x M. sexmaculatus (Adult). Intraspecific cannibalism among different instars and adult of C. transversalis and M. sexmaculatus in absence of prey was the highest in C. transversalis (Adult) x C. transversalis (3rd) combination where as, C. transversalis (Adult) consumed only 33.30%. In case of Interspecific predation among different instars and adult of C. transversalis and M. sexmaculatus in absence of prey, C. transversalis (Adult) showed highest consumption rate of 40.00% followed by C. transversalis (4th) with 33.30%.ThesisItem Open Access ECOLOGY OF APHID VECTORS OF CITRUS TRISTEZA VIRUS(2020-07) CHANGKIRI, MAONGKAR T.; Patgiri, P.A field survey was conducted to study the incidence of citrus tristeza virus (CTV) and its aphid vectors, in different citrus growing locations of Assam and Nagaland. 190 samples were collected from four districts of Assam (Jorhat, Tinsukia, Sivasagar and Golaghat) and two districts of Nagaland (Mokokchung and Wokha). Citrus leaf samples were used for detection of CTV infection by double antibody sandwich-enzyme linked immuno-sorbent assay (DASELISA) and Reverse Transcriptase Polymerase Chain Reaction (RT-PCR). According to the results, 75 per cent CTV disease incidence was detected in surveyed areas of Assam and 24.55 per cent CTV disease incidence was detected in Nagaland. District wise, the highest CTV disease incidence (96.67 %) was detected in Tinsukia district of Assam and the lowest (21.43 %) was detected in Mokokchung district of Nagaland. RT-PCR confirmed the results of DASELISA. The survey result also indicated the presence of the vector Toxoptera citricida in all the locations. The elevations of the different location surveyed ranged from 79-1130 m AMSL. The study on population dynamics of T. citricida, revealed that the aphid reached its highest peak population of 416.68 on the 4th of June, during 2017 and 431.28 on 15th May, during 2018. T. citricida was observed to have two population peaks per year. The minimum temperature was the most dominant factor which showed positive and significant correlation, for mean population of T. citricida. 15 species of coccinellid predators and one species of syrphid were observed in the field plot of Assam Lemon and Micraspis discolor, Cheilomenes sexmaculata, Coelophora bisellata and Coelophora saucia, were the most abundant and they were found actively feeding on T. citricida. The population of T. citricida, showed positive and significant correlation, with all four coccinellid beetles, indicating that the populations of the predators, increased or decreased with the abundance or scarcity of T. citricida. The data on the two year study of the biology of the four coccinellid beetles revealed that the longest incubation period (3.43 ± 0.07 days) was recorded on C. sexmaculata. The longest total larval period (11.52 ± 0.26 days) was recorded on C. sexmaculata. The longest pupal period (3.90 ± 0.08 days) was recorded on C. sexmaculata. The longest total developmental (egg to adult emergence) period was recorded on C. sexmaculata, with an average duration of 18.85 ± 0.31. C. sexmaculata had the longest adult longevity with an average of 50.90 ± 1.16 days and the longest total life cycle (69.75 ± 1.17 days) was recorded on C. sexmaculata. Pooled data analysis of the two year study of predatory efficiency of the four coccinellid beetles reared on T. citricida, indicated that there was significant difference among the different predators. It was observed that the feeding potential of all the beetles increased gradually through each larval stage with the fourth being the most voracious. The predatory efficiency of the larval stages of the four coccinellid beetles from highest to lowest was recorded in the following order. C. sexmaculata (27.04 ± 0.32) > C. bissellata (24.63 ± 0.23) > C. saucia (23.44 ± 0.26) > M. discolor (20.13 ± 0.17). The predatory efficiency of the adult stages of the four coccinellid beetles from highest to lowest was recorded in the following order. C. saucia (82.66 ± 0.69) > C. bissellata (78.94 ± 0.81) > C. sexmaculata (66.36 ± 0.83) > M. discolor (53.01 ± 0.59).ThesisItem Open Access BOTANICALS FOR TEA INSECT PEST MANAGEMENT(2020-09) Mahanta, Ritushree; Kalita, SurajitThe experiment on bioefficacy of Annona squamosa (L.) (Family: Annonaceae), Adhatoda vasica (L.) (Family: Acanthaceae), Cascabela thevetia (L.) Lippold (Family: Apocynaceae), Datura stramonium (L.) (Family: Solanaceae) and Lawsonia inermis (L.) (Family: Lythraceae) leaf extracts conducted at Department of Entomology, Assam Agricultural University, Jorhat during 2018-20 revealed a dose- and time-dependent mortality of red spider mite (RSM), Oligonychus coffeae Nietner (Tetranychidae: Acarina) and tea mosquito bug (TMB), Helopeltis theivora Waterhouse (Miridae: Hemiptera) attacking tea plantation. The leaves of the selected insecticidal plants were collected from the Jorhat district of Assam; which were later macerated and extracted with standard procedure in distilled water on weight/volume basis for preparation of desired concentrations through serial dilution method viz., 0.1%, 0.5%, 0.75%, 1.0%, 2.5%, 5.0%, 7.5%, 10.0%. Neem Seed Kernel Extract (NSKE) 0.15% EC 2 5 ml/litre of water as standard check along with a control (water) were also taken for toxicity comparison. The treatments were replicated thrice and the data on adult mortality were recorded at 6, 12, 24, 48 and 72 hours after treatment (HAT). Moreover, plant extracts at different concentrations were also tested for ovicidal activity against O. coffeae. Tea leaves were also tested for any change in biochemical properties of tea leaves after application of botanicals to control H. theivora and O. coffeae at Phytochemistry Laboratory, Department of Biochemistry & Agricultural Chemistry, AAU, Jorhat during 2018-20. Best three plant extracts showing lowest LC50 values against the test insects were considered for biochemical investigation and data were recorded at 1,3, 5 and 10 days after spraying (DAS) of botanicals with three replications. The results on bioefficacy revealed the strong acaricidal properties of D. stramonium recording 90.00% mortality of O. coffeae adults, while L. inermis has been found to be having strong insecticidal properties against H. theivora adults recording 80.00% mortality at 72 hours after treatment (HAT). The water extract of D. stramonium had the highest ovicidal properties causing complete inhibition of hatching of O. coffeae eggs even upto 5.00% concentration as against 91.32% hatching in the control, which was followed by A. vasica recording 25.93% hatching at 5.00% concentration as compared to 93.03% hatching in the control. 6 The order of toxicity of botanicals against O. coffeae in terms of LC50 values was D. stramonium (0.270%)>A. vasica (1.979%) >L. inermis (2.085%) > C. thevetia (3.740%) > A. squamosa (3.942%); while the order of toxicity in case of H. theivora was found to be L. inermis (1.052%)>D. stramonium (2.228%) >C. thevetia (2.296%) >A. vasica (2.644%) >A. squamosa (4.534%). The best three botanicals based on their LC50 values viz., Lawsonia inermis (1.052%), Datura stramonium (2.228%) and Cascabela thevetia (2.296%) for H. theivora and for O. coffeae the botanicals viz., Datura stramonium (0.270%), Adhatoda vasica (1.979%) and Lawsonia inermis (2.085%) were tested for biochemical parameters including chlorophyll a & b, carotenoids, reducing sugar and polyphenols along with healthy leaf sample and found that the reducing sugar content in TMB and RSM infested tea leaves decreased upon application of D. stramonium leaf water extracts to 1.592 mg/100g and 3.477 mg/100g, respectively at 10 DAS as compared to control (6.566 mg/100g & 5.487 mg/100g respectively). Whereas, the polyphenol content in TMB and RSM infested tea leaves decreased upon application of treatment with L. inermis and D. stramonium leaf water extracts to 3.967 mg/100g and 3.247 mg/100g, respectively on 10 DAS as compared to the control (8.470 mg/100g & 6.773 mg/100g respectively). The chlorophyll a, chlorophyll b and carotenoids contents in both TMB and RSM infested tea leaves was found to have decreased upon application of D. stramonium leaf extracts.
