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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).
