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Acharya N G Ranga Agricultural University
Studies on “Phosphine resistance monitoring, molecular characterization and management of Tribolium spp. in stored rice” was conducted at Department of Entomology, S.V. Agricultural College, Tirupati and Institute of Frontier Technology, Regional Agricultural Research Station (RARS), Tirupati, Acharya N.G. Ranga Agricultural University (ANGRAU), Andhra Pradesh, India during the year 2021-22. The red flour beetle, Tribolium castaneum was collected from warehouses located in seven different districts of Andhra Pradesh viz., Nellore, Chittoor, Guntur, Krishna, Godavari, Kurnool and Srikakulam. Laboratory reared susceptible populations collected from RARS, Tirupati storage godown have been maintained for six to seven generations in insectary, Department of Entomology, S.V. Agricultural College, Tirupati and used for bioassay studies using modified FAO method (FAO, 1980). All the seven test populations were found to be resistant to phosphine, but varied in their level of resistance compared to susceptible lab population. There was no mortality recorded in the untreated control. Probit analysis estimated LC50 and LC99 values at 0.80 and 3.86 ppm for laboratory susceptible population respectively. The LC50 for different Tribolium populations ranged between 25.38 ppm (Nellore population) to 69.95 ppm (Kurnool population) corresponding to 31.76 and 87.54 fold resistance compared to susceptible laboratory population. xxi Red flour beetle populations collected from eight different locations were also molecularly characterized through total genomic DNA method using partial mitochondrial COI gene. The multiple nucleotide sequence analysis of mitochondrial gene sequences of eight populations revealed that, Chittoor (T-2022-Ctr), Krishna (T-2022- Krs) and Nellore (T-2022-Nlr) population shared 100 per cent similarity with Indian populations of T. castaneum from Kerala (MT506942 and MT499228) and Maharashtra (MH910055) and T. castaneum population from Bangladesh (MK411585), Germany (KM439779) and South Korea (ON482353) while 99.8 per cent similarity with T. castaneum-complete genome (KM244661) sequence from China. The mitochondrial COI gene sequences of all the eight populations collected from Andhra Pradesh were submitted to NCBI (GenBank) and allotted with accession number viz., Nellore (ON811628), Chittoor (OP024180), Guntur (ON869466), Krishna (ON797460), Godavari (ON920194), Kurnool (ON811639), Srikakulam (OP021501) and susceptible lab population (ON869467). Different life stages of red flour beetle viz., larva, pupa and adult stages were irradiated at different doses of gamma radiation viz., 10, 25, 50, 70, 100, 250, 450 and 1000 Gy or left unirradiated as a control using Cobalt-60 Gamma irradiator (Gamma Chamber 5000) facility available at ICAR-Indian Institute of Horticultural Research (IIHR), Bengaluru. Mortality of adults was recorded at different time intervals, 1000 Gy resulted in 100 per cent mortality after one week indicating that dose killed the beetles efficiently compared to 3 to 4 months survival of Tribolium adults in the untreated control. Radiation dose of ≥ 50 Gy resulted in complete sterility of adults and 100 per cent pupal mortality. There was no F1 adult emergence observed in the irradiated adults. The decreased survival of emerged adults was recorded with increase in radiation dose and the emerged adults were not survived from irradiated pupae at ≥ 250 Gy. Among different life stages, Tribolium larvae were found to be more susceptible to gamma irradiation with 100 per cent mortality at 250 Gy after two weeks. None of the larvae had developed into pupae with irradiation dose of 100 Gy and above. There was no adult emergence from the irradiated grubs at all the test doses from ≥ 10 Gy. Weight loss of rice infested with immature stages or adult beetles was significantly reduced by irradiation treatment whereas 4.74 per cent weight loss was recorded with untreated control after two months. xxii The green synthesis of nano silica encapsulated bioformulations of neem-azal, acorus oil and clove oil was done using dynamic light scattering technique which formed the more effective nanoparticles with sizes of 42.2 nm, 130.9 nm and 112 nm and zeta potential of 10.8 mV, -27.4 mV and -61.5 mV respectively compared to nano silica with 69.4 nm particle size and -23.4 mV zeta potential. Effect of nanoformulations and plant products viz., neem-azal, clove oil, acorus oil, nano silica, nano chitosan, nano silica encapsulated neem-azal, nano silica encapsulated clove oil and nano silica encapsulated acorus oil were evaluated against larvae and adults of Red flour beetle, T. castaneum. Among all biopesticides tested, nano silica encapsulated essential oils were found to be most promising against T. castaneum as compared to normal essential oils. Among the nano formulations, nano neem-azal was found very effective against Tribolium larvae and adults with 100 per cent mortality after 15 days of exposure even in lowest test concentration