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Assam Agricultural University, Jorhat
Assam Agricultural University is the first institution of its kind in the whole of North-Eastern Region of India. The main goal of this institution is to produce globally competitive human resources in farm sectorand to carry out research in both conventional and frontier areas for production optimization as well as to disseminate the generated technologies as public good for benefitting the food growers/produces and traders involved in the sector while emphasizing on sustainability, equity and overall food security at household level.
Genesis of AAU -
The embryo of the agricultural research in the state of Assam was formed as early as 1897 with the establishment of the Upper Shillong Experimental Farm (now in Meghalaya) just after about a decade of creation of the agricultural department in 1882. However, the seeds of agricultural research in today’s Assam were sown in the dawn of the twentieth century with the establishment of two Rice Experimental Stations, one at Karimganj in Barak valley in 1913 and the other at Titabor in Brahmaputra valley in 1923. Subsequent to these research stations, a number of research stations were established to conduct research on important crops, more specifically, jute, pulses, oilseeds etc. The Assam Agricultural University was established on April 1, 1969 under The Assam Agricultural University Act, 1968’ with the mandate of imparting farm education, conduct research in agriculture and allied sciences and to effectively disseminate technologies so generated. Before establishment of the University, there were altogether 17 research schemes/projects in the state under the Department of Agriculture. By July 1973, all the research projects and 10 experimental farms were transferred by the Government of Assam to the AAU which already inherited the College of Agriculture and its farm at Barbheta, Jorhat and College of Veterinary Sciences at Khanapara, Guwahati.
Subsequently, College of Community Science at Jorhat (1969), College of Fisheries at Raha (1988), Biswanath College of Agriculture at Biswanath Chariali (1988) and Lakhimpur College of Veterinary Science at Joyhing, North Lakhimpur (1988) were established. Presently, the University has three more colleges under its jurisdiction, viz., Sarat Chandra Singha College of Agriculture, Chapar, College of Horticulture, Nalbari & College of Sericulture, Titabar. Similarly, few more regional research stations at Shillongani, Diphu, Gossaigaon, Lakhimpur; and commodity research stations at Kahikuchi, Buralikson, Tinsukia, Kharua, Burnihat and Mandira were added to generate location and crop specific agricultural production packages.
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ThesisItem Open Access NUTRITIONAL PROFILING OF SOME EDIBLE SERICIGENOUS INSECTS OF MANIPUR(2023) Singha, Th. Aruna; Bhattacharyya, BadalLaboratory experiments were carried out to assess the nutritive value of four edible sericigenous insect species viz., Bombyx mori L., Anthrerea proylei J., Antherea frithi M. and Cricula trifenestrata H. based on their proximate & elemental content, amino & fatty acid profiles, antioxidant & anti-nutritional properties as well as their microbial aspects in the Soil Arthropod Pests Laboratory, Department of Entomology, Post Graduate Laboratory, Department of Biochemistry and Agricultural Chemistry, Department of Plant Pathology, Assam Agricultural University, Jorhat during 2019-2022. Edible sericigenous insect species cocoons were collected from various locations covering five districts of Manipur. The powdered samples of the pupae were considered for biochemical and microbial analysis. The proximate analysis of four edible sericigenous insect species had significant variation. The moisture content ranged from 2.038-6.075 per cent and the highest moisture content was observed in A. proylei (6.075%) and A. frithi registered the least moisture content (2.038%) indicating that suitability of sericigenous pupal powder for preservation for a reasonable period of time without any probable risk of any microbial deterioration. The carbohydrate content of the studied species was found maximum (12.130%) in C. trifenestrata and the lowest (2.250%) was recorded in A. proylei. Appreciable amounts of crude protein content were estimated in all the studied species which ranged from 59.315- 69.418 per cent. The highest (69.418%) crude protein was registered in A. frithi and it was found to be significantly superior over the rest of the species. The estimated crude protein content of A. proylei, C. trifenestrata and B. mori were 65.383, 61.463 and 59.315 per cent, respectively. Crude fat content registered in the studied species varied significantly and ranged from 19.213-30.725 per cent. The highest (30.725%) crude fat content was recorded in B. mori followed by A. proylei (29.750%) and C. trifenestrata (28.738%), whereas A. frithi recorded the lowest (19.213%) amount of crude fat content. The crude fibre content varied from 2.213-8.450 per cent and C. trifenestrata registered a significantly high amount of crude fibre (8.450%), whereas the lowest was found in B. mori (2.213%). The highest (5.275%) ash content was observed in A. proylei, whereas the lowest (4.175%) was registered in C. trifenestrata. The ash content of mulberry silkworm B. mori (5.150%) was statistically at par with the A. frithi (5.150%). While analyzing the energy content (kcal/100 g) of all the four species, the maximum energy content (560.205) was estimated in A. proylei followed by C. trifenestrata (556.035) and B. mori (534.885), whereas A. frithi detected the lowest energy content of 465.453 kcal/100 g. Altogether 9 minerals as elemental composition were estimated in all the studied species. The mineral analysis indicated that the concentration of macro elements viz., potassium, calcium and magnesium were significantly higher in A. frithi (70.295, 13.993 & 25.889 mg/100 g), whereas the lowest amount (65.663, 8.790 & 23.526 mg/100 g) potassium, calcium and magnesium were observed in C. trifenestrata. However, the highest sodium and phosphorus content (36.026 & 22.429 mg/100 g) were recorded in B. mori and the least amount of sodium (26.489 mg/100 g) and phosphorus (16.062 mg/100 g) were found in C. trifenestrata. Considerable amounts of micro elements like iron was recorded the highest (26.639 mg/100 g) in B. mori. The lowest iron content was observed in A. proylei (8.315 mg/100 g). Zinc, manganese and copper content (mg/100 g) was estimated to be the highest (21.709, 5.445 and 3.123) in A. frithi which showed statistical superiority over other species whereas C. trifenestrata registered with the lowest zinc (15.381 mg/100 g), manganese (1.209 mg/100 g) and copper (0.997 mg/100 g) content. Among all the amino acids 19 common amino acids, 8 were found essential. Glutamic acid was found to be the most abundant (8.88-7.25%) in all the four species followed by aspartic acid (7.83-5.95%). Among the species, the concentration of glutamic and aspartic content was found to be highest in the A. frithi (8.88 & 7.83%). The range of Essential Amino Acids (EAAs) viz., leucine (3.95-5.76%), valine (3.11-4.22%), isoleucine (2.29-3.29%), lysine (3.65-4.40%), threonine (2.63-3.71%) and phenylalanine (2.90-4.40%) are found in significant amounts. Both the sulphur containing amino acids (methionine and cysteine) were found in relatively low amounts and varied from 1.27-1.95 and 0.35-0.48 per cent. Glycine, alanine and serine were also available in appreciable amounts with values ranging from 3.09-5.87, 3.87-5.48 and 4.52-4.99 per cent, respectively. In case of sweet amino acids (i.e., alanine & glycine), the highest amount was recorded in B. mori (5.48 & 5.87%) but lowest (3.87 & 3.09%) in A. frithi. Most of the amino acid concentration was found to be the highest in A. frithi followed by A. proylei, C. trifenetrata and B. mori, respectively. Total fatty acid analysis revealed that the highest amount of Saturated Fatty Acids (SFA) and Monounsaturated Fatty Acids (MUFA) were recorded in C. trifenestrata (6.69 & 5.26%) followed by A. proylei (4.43 & 4.28%), B. mori (2.38 & 2.70%) while the lowest SFA and MUFA was registered in A. frithi (0.80 & 0.35%). On the contrary, the highest (8.36%) Polyunsaturated Fatty Acids (PUFA) was evaluated in A. proylei followed by C. trifenestrata (7.90%), B. mori (4.36%) and the least amount (0.39%) was recorded in A. frithi. Altogether, 18 fatty acids were registered in A. frithi which was followed by A. proylei and C. trifenestrata (9 nos.) and B. mori (6 nos.). Linoleic and alpha linolenic acid content (2.48 & 5.88%) were found maximum in the A. proylei followed by C. trifenestrata (2.07 & 5.83%) and B. mori (0.78 & 3.58%) while the least linoleic and alpha linoleic acid (0.25 & 0.14%) was observed in A. frithi. In regards of antioxidant properties, phenol (mg catechol equivalent/g), flavonoid (mg quercetin equivalent/100 g) and antioxidant activity (% DPPH inhibition) were found in all the species and varied from 37.261-92.400, 27.223-35.489 and 35.914-74.587, respectively. Cricula trifenestrata showed the highest phenol and flavonoid content (92.400 mg catechol equivalent/g & 35.489 mg quercetin equivalent/100 g) and which was found to be significantly superior over rest of the species. Antioxidant activity was observed to be the highest in A. frithi (74.587% DPPH inhibition) and least in the C. trifenestrata (35.914% DPPH inhibition). The variability in the concentration of tannin, phytic acid and oxalic acid were ranged from 3.280-6.201 mg tannic acid equivalent/100 g, 2.780-5.238 mg/100 g, 1.762-4.138 mg/100 g, respectively. As regards to anti-nutritional compounds, the highest tannin (mg tannic acid equivalent/100 g), phytic acid (mg/100 g) and oxalic acid (mg/100 g) were observed in B. mori (6.201, 5.238 & 4.138) followed by A. proylei (5.702, 4.510 & 3.572), C. trifenestrata (5.468, 3.304 & 2.819) and A. frithi (3.280, 2.780 & 1.762), respectively. However, the presence of anti-nutritional properties in all four edible insect species were detected much more below the recommended range of 250-500 mg/100 g. Microbial enumeration revealed that total viable counts of B. mori, A. proylei and A. frithi silkworm pupal powders stored under ambient temperature (28 to 32°C) had higher bacterial population (3.331, 3.073 & 3.095 log cfu/g), whereas the least bacterial counts (2.639, 2.520 and 2.564 log cfu/g) of B. mori, A. proylei and A. frithi silkworm were observed when they stored under temperature (-16 to -21°C). Cricula trifenestrata recorded the highest population of bacteria (2.870 log cfu/g) under the temperature (15 to 20°C) and least (2.075 log cfu/g) under the temperature (-16 to -21°C). The highest yeast and mould population (3.102, 3.069, 2.855 & 2.714 log cfu/g) was observed when B. mori, A. proylei A. frithi and C. trifenestrata pupal powder were stored at -16 to -21°C. Microbial enumeration showed that B. mori pupal powder had the highest microbial contamination among the other studied sample. Total viable counts were under the advised limit of fresh minced meat (< 6 log cfu/g, TAC). Through microbial test kits, it was further confirmed the absence of two most common food borne pathogens i.e., Escherichia coli and Salmonella sp. in all the studied sericigenous insect samples.ThesisItem Open Access DIVERSITY, POPULATION DYNAMICS AND MANAGEMENT OF INSECT PESTS OF TEA(2023) Rabha, Himadri; Dutta, B. C.Diversity study of insect pest complex of tea was carried out at three agroclimatic zones of Assam viz.,Upper Brahmaputra Valley Zone (Jorhat) North Bank Plain Zone (Udalguri) and Lower Brahmaputra Valley Zone (Kokrajhar) during 2019-20, 2020-21 and 2021-22, respectively. Laboratory experiments were carried out at Biocontrol laboratory, Department of Entomology, Assam Agricultural University and at laboratory of Krishi Vigyan Kendra, Udalguri. The field experiment was conducted in the tea garden of Udalguri district during 2021-22. Survey results revealed that a total of 4 mites and 22 different insect species belonging to 7 orders and 19 families were found to be associated with tea as recorded from different locations of Assam. In addition, 7 species of insects were found to be as visitors of the tea ecosystem in different period of time. Moreover, 11 different types of natural enemies were also observed. Among the sucking insect pests, per cent infestation of tea mosquito bug was recorded maximum (43.22 per cent) in Jorhat district. Among defoliator pests, per cent infestation of looper caterpillar was recorded maximum (34.23 per cent) in Udalguri district. Among all the insect and mite pests, tea mosquito bug showed highest degree of infestation in Jorhat i.e., 46.21 per cent whereas in case of red spider mite and looper caterpillar, highest degree of infestation was recorded 54.80 and 46.32 per cent in Udalguri district, respectively. Among all the insect and mite pests recorded during the study, tea mosquito bug, red spider mite and looper caterpillar showed moderate (34-66 per cent) degree of infestation, so they are considered as major pests. During 2019-20, the species richness in Jorhat showed maximum value of 1.50 in defoliator pests. The variation of species richness indices indicated a highest value of 1.54 and 1.50 in Udalguri during 2020-21 and 2021-22 in defoliator pests, respectively. Whereas, in Kokrajhar, the highest value was 1.55 in sucking pests (2020-21) and 1.59 in defoliator pests (2021-22). Shannon- Wiener index revealed that the highest value of 2.21 in defoliator pests in Jorhat (2019-20). During 2020-21, in Udalguri, it was found to be highest in sucking pests with value 2.10 and 2.21 in Kokrajhar, respectively. During 2021-22, Shannon- Wiener index showed highest value of 2.10 in Udalguri district and 2.12 in Kokrajhar district in defoliator insect pests. In terms of Simpson’s diversity index, highest value of 0.87 was recorded in defoliator insect pests in Jorhat district (2019-20). Likewise, during 2020-21, in Udalguri and Kokrajhar district, the highest diversity value of 0.82 and 0.87 were recorded in sucking pests, respectively. During 2021-22, the highest diversity values of 0.86 and 0.87 were recorded in defoliator pests in Udalguri and Kokrajhar, respectively. In Jorhat (2019-20), the maximum number of tea mosquito bug was observed to be 5.9 per bush during the first week of September. The highest population indices record of 20.27 mites per leaf was recorded during third week of November. The maximum number of looper caterpillar was observed to be 4.26 per bush during fourth week of February. Correlation studies between weather parameters and population indices of tea mosquito bug showed significant positive correlation with maximum temperature, minimum temperature, evening relative humidity and rainfall whereas, red spider mite showed significant positive correlation with maximum temperature and negative correlation with morning relative humidity, evening relative humidity and total rainfall. The population indices of looper showed significant positive correlation with morning relative humidity. In Udalguri (2020-21), the maximum population indices of tea mosquito bug, red spider mite and looper caterpillar were recorded as 5.12 per bush during the last week of August, 14.78 per leaf during March to April and 5.02 per bush during second week of March, respectively. Correlation studies between weather parameters and population indices of tea mosquito bug showed significant positive correlation with maximum temperature, minimum temperature and evening relative humidity. The population indices of red spider mite showed significant positive correlation with maximum temperature, whereas, it showed negative correlation with morning relative humidity, evening relative humidity and total rainfall. The looper caterpillar population showed negative correlation with maximum temperature, minimum temperature, evening relative humidity and total rainfall. During 2021-22, the maximum population indices of tea mosquito bug, red spider mite and looper caterpillar were recorded to be 5.79 per bush, 28.12 per leaf, 5.23 per bush, respectively. Correlation studies between weather parameters and population indices of tea mosquito bug showed significant positive correlation with maximum temperature, minimum temperature, evening relative humidity and total rainfall. Red spider mite showed significant positive correlation with maximum temperature and negative correlation with total rainfall whereas, looper caterpillar showed significant negative correlation with maximum temperature, minimum temperature and total rainfall. In Kokrajhar (2020-2021), the maximum population indices of tea mosquito bug, red spider mite and looper caterpillar were recorded to be 4.12 per bush, 27.23 per leaf, 4.12 per bush respectively. Correlation studies between weather parameters and population indices of tea mosquito bug showed significant positive correlation with maximum temperature, minimum temperature, evening relative humidity and rainfall, whereas red spider mite showed non-significant positive correlation with maximum temperature and looper showed significant negative correlation with minimum temperature and total rainfall. During 2021-22, the maximum population indices of tea mosquito bug, red spider mite and looper caterpillar were recorded to be 5.30 per bush, 14.52 per leaf and 10.22 per bush, respectively. Correlation studies between weather parameters and population indices of tea mosquito bug showed a negative correlation with morning relative humidity, evening relative humidity and total rainfall. Red spider mite showed significant positive correlation with maximum temperature and negative correlation with morning relative humidity, evening relative humidity and total rainfall whereas looper caterpillar showed significant negative correlation with maximum temperature, minimum temperature, morning relative humidity, evening relative humidity and total rainfall. Laboratory study on efficacy of different plant extracts against tea mosquito bug showed the highest mortality of 80.00 per cent in case of Pongamia pinata in 120 hours after treatment. The results on efficacy of different plant extracts against adult red spider mite showed that the highest mortality was recorded 93.33 per cent in case of both the treatments of Vitex negundo and Azadirachta indica at 120 HAT. Similarly, bio efficacy of different plant extracts against looper caterpillar showed that the larval mortality was highest with value 86.67 per cent at 120 HAT in case of A. indica. The results on efficacy of plant extracts at field condition reveals that at seven days after spraying, P. pinata recorded the least number of populations of tea mosquito bug with 0.67 number per bush. Again, at seven days after spraying, least number of mites was recorded in case of V. negundo with 7.19 mites per leaf. Moreover, the results showed that the maximum reduction of larval population was found in A. indica with 1.72 looper caterpillar population per bush at seven days after spraying.ThesisItem Open Access MANAGEMENT OF GREATER WAX MOTH, Galleria mellonella (LEPIDOPTERA: PYRALIDAE) AND CHARACTERIZATION OF ITS GUT BACTERIA(2020) Rokozeno; Deka, Mukul KumarField and laboratory experiments were carried out at the Department of Entomology and Department of Agricultural Biotechnology, Assam Agricultural University, Jorhat during 2018 and 2019 to study the management of greater wax moth, Galleria mellonella (Lepidoptera: Pyralidae), a serious pest of the honey bee using different integrated modules and to characterized the gut bacterial community. Different life stages of the wax moth were studied to provide a concise information on the population trend. Laboratory studies confirmed the occurrence of multiple generations of G. mellonella in a year. In the present study, five generations of G. mellonella were recorded in a single year. The duration of each developmental stages showed variation in each generation. Mean incubation period was found to be 4.60 ± 0.49 days (1st generation), 4.40 ± 0.49 days (2nd generation), 3.20 ± 0.40 days (3rd generation), 4.20 ± 0.75 days (4th generation) and 8.00 ± 0.63 days in the 5th generation. Throughout each generation a total 6 (six) numbers of larval instars were recorded. Mean duration of the total larval period was observed to be 32.40 ± 2.33 days (1st generation), 25.20 ± 0.40 days (2nd generation), 25.40 ± 1.62 days (3rd generation), 25.60 ± 1.36 days (4th generation) and 45.80 ± 1.17 days (5th generation). The mean duration of the pre- pupal period was recorded to be 5.20 ± 0.75 days (1st generation), 3.40 ± 0.49 days (2nd generation), 3.80 ± 0.75 days (3rd generation), 4.20 ± 0.40 days (4th generation) and 10.60 ± 0.80 days (5th generation). The mean duration of the pupal period was found to be 9.80 ± 1.17 days (1st generation), 9.60 ± 0.49 days (2nd generation), 8.00 ± 0.63 days (3rd generation), 8.60 ± 0.49 days (4th generation) and 18.00 ± 1.67 days in the last generation. The longevity of the male adult wax moth recorded a mean duration of 17.80 ± 0.75 days (1st generation), 20.60 ± 1.02 days (2nd generation), 20.20 ± 0.75 days (3rd generation), 21.40 ± 1.02 days (4th generation) and 8.40 ± 0.80 days (5th generation).The adults recorded a longer period of longevity over the adult female moths. The longevity of the adult female moth recorded a mean duration of 10.40 ± 2.33 days (1st generation), 11.40 ± 1.85 days (2nd generation), 11.20 ± 0.40 days (3rd generation), 11.20 ± 0.40 days (4th generation) and 13.40 ± 1.02 days (5th generation). The larval stages of wax moth are the damaging stage of the pest, in order to manage them, different integrated module incorporating cultural, biological and cold treatment was carried out. In determining the effectiveness of different integrated modules, all the treatments were found to be effective over the control. Combs kept in deep freezer at - 7°C recorded least damage of 1.53 per cent comb in the initial period however, with the elapsing of time Bt. var. kurstaki at 1 per cent in module III(b) proved to be better over the other modules. Pertaining to larval mortality, Bt. var. kurstaki at 1 per cent showed highest mortality as compared to the other modules and exhibited mortality per cent up to 36.66 per cent. In the context of reducing adult emergence as a measure of managing wax moth, the least per cent adult emergence of 33.33 per cent was recorded in module III where Bt. var. kurstaki @1 per cent was incorporated. All the modules comparatively showed satisfactory performance in managing the wax moth over the control in which no external intervention was employed. For best preventive measures all the modules can be suggested, with emphasis on regular and timely monitoring. For an effective and desirable management, module III with Bt. var. kurstaki at 1 per cent would be recommended against the pest. G. mellonella larva has been reportedly known to degrade polyethylene (PE), as such it has been assumed that certain microbes residing in the gut may be responsible. The investigation of the gut led to the isolation of 14 microbial isolates. The morphological characteristics of the fourteen isolates were mostly circular in shape, and had an entire margin, the colony color was chiefly white with raised elevation and exhibited smooth surface. Utilising 16S rRNA sequencing and analysing them on BLAST, the isolates were identified: it constituted of thirteen numbers of bacteria and one microalgae. The bacterial species ascertained were shown to be 2 strains of Acinetobacter radioresistens, 2 strains of Bacillus circulans, 2 strains of Enterococcus faecalis, Agrobacterium sp., Exiguobacterium aestuarii, Microbacterium zeae, Microbacterium paraoxydans, Sphingomonas pseudosanguinis, Sphingobium yanoikuyae, and one number of uncultured bacterium. The lone algae out of the 14 (fourteen) microbes isolated was confirmed as Picochlorum oklahomensis. A number of the above species has been reportedly known to degrade aromatic hydrocarbon, low density polyethylene, high density polyethylene, polystyrene etc. The precise mechanism of this microbes in degrading PE, function of the host i.e. G. mellonella larva and the microbes in degrading the plastic whether individually or together, merits further investigation. The process of PE degradation could be used to devise a biotechnological solution on an industrial scale for managing polyethylene waste.ThesisItem Open Access Diversity of mites in promising flower crops and their management in Gerbera, Gerbera jamesonii Bolus(2021) Altaf, Nilofar; Rahman, S.Mites are among the most diverse arachnid group in terrestrial ecosystem. Therefore, a survey was carried out during the year 2018-2020 on “Diversity of mites in promising flower crops and their management in gerbera, Gerbera jamesonii Bolus in five different districts under Upper, Central and Lower Brahmaputra Valley Zones of Assam to know the diversity of phytophagous mites attacking flower crops. A random survey was carried out at different locations covering five different districts of Assam. The infested leaves were brought to the Acarology Laboratory, Dept of Entomology, AAU, Jorhat for the identification of different mite species collected from different flower crops like rose, gerbera, hibiscus, anthurium, orchid and marigold. A total of five different mite species belonging to the family Tetranychidae viz., Tetranychus pacificus McGregor, T. truncatus Ehara, T. okinawanus Ehara, T. bunda Flechtmann and T. piercei McGregor and five species under the family Tenuipalpidae viz., Brevipalpus californicus Banks, B. chilensis Baker, B. yothersi Baker, B. lewisi McGregor and B. obovatus Donnadieu were recorded. However, B. yothersi, T. bunda, T. pacificus and T. piercei are supposed to be new record from our country. Out of five districts, maximum number of 5463 individuals was collected from Kamrup district. The species diversity index (1.582) and richness indices (0.587) of mite species was found to be highest in Experimental Farm, Dept of Horticulture, Assam Agricultural University of Jorhat district, whereas the lowest species diversity index (0.342) and richness indices (0.133) were observed in Changamari Habigaon of Dibrugarh district. In case of Pielou’s eveness index for phytophagous mites, highest value of 0.892 was recorded from Potia gaon of Jorhat district and lowest value of 0.494 was recorded from Changamari Habigaon of Dibrugarh district. The major mite species collected from different locations during survey were brought to the Acarology laboratory, Dept of Entomology, AAU, Jorhat for morphometric study. The body measurements were taken under labovision phase contrast microscope. The study revealed that the male of T. pacificus possessed highest body length of 371.207±0.001μm compared to the females with body length of 289.625±0.003μm whereas lowest body length of 338.354±0.001μm was observed in the male of T. okinawanus. The morphometric study of the major false spider mite species revealed that the B. obovatus showed the highest body length of 287.392±0.001μm whereas the lowest body length of 269.257±0.400μm was observed in B. yothersi. The principal component analysis was done under SPSS 20.0 Statistical package which showed that in case of adult false spider mite species among 25 morphometric characters used for analysis of variance two parameters, viz., length of body and width of body significantly contributed towards variation among them. The Principal Component Analysis of two different morphometric characters indicates two Eigen values which were greater than one that explained 81.977 per cent variation amongst the false spider mite species. In case of adult male and female of spider mite species among 22 morphometric parameters used for analysis of variance, four parameters viz., body length, body width, length of gnathosoma and length of leg I significantly contributed towards variation among them. The principal component analysis of four different morphometric characters indicates four Eigen values which were greater than one that explained 93.590 per cent variation amongst the male and female spider mite species. As regards the management strategies, efficacy of different treatments, viz., Polygonum hydropiper L (aqueous and ethanol extract), biopesticides like Beauveria bassiana Vuill (Green Beauveria), Metarhizium anisopliae Sorokin (Green Meta), pestoneem, predatory mite, (Neoseiulus longispinosus),chemical like spiromesifen 240 SC as check were evaluated against T. truncatus in gerbera under Polycarbonate house, AINP on Agril. Acarology, AAU, Jorhat. Randomly selected leaves from each plot were brought to the laboratory and studied under Stemi 2000C microscope. The number of mites was recorded one day before and at 1, 3, 5 and 7 days after application of treatments. Out of these treatments, pestoneem (0.3%) was found to be most effective against mite population which resulted in 94.90 per cent reduction in 7 days after spraying in the year 2019 and 95.77 per cent reduction in the year 2020.ThesisItem Open Access Bio-ecological approaches for management of major insect pests in rice ecosystem(2022) Baruah, Mayuri; Dutta, Bijon ChandraAs biotic stress, especially insect pest is one of the most considerable limiting factors of rice productivity, a field study was carried out in the rice field of Regional Agricultural Research Station, Assam Agricultural University, Titabar, Jorhat to investigate the relative abundance of major insect pests as well as the effects of abiotic factors on their damage incidence in seven high yielding varieties, Ranjit, Ranjit Sub-1, Bahadur, Bahadur Sub-1, Gitesh, Swarna Sub-1 and Shraboni in kharif and rabi season during 2018-2020 with an aim to formulate sustainable management strategies against major insect pests in rice. White stem borer (47.49%) was the most predominantly abundant species followed by yellow stem borer (41.97%) among seven major insect pest species including leaf folder, gall midge, caseworm, whorl maggot and gundhi bug observed throughout all the growth stages of rice both in kharif and rabi season. Both the species of stem borer gradually increased and reached peak at reproductive stage due to availability of enough food and then decreased and again increased in the ripening stage during both the season. The relative abundance of white stem borer varied from 38.23 per cent to 47.49 per cent in the seven varieties recorded higher population in rice variety, Shraboni and lower in Gitesh at reproductive stage in rabi season. Rice leaf folder was the most abundant leaf feeder and its population abundance varied from 6.30 per cent to 6.61 per cent in Ranjit Sub -1, Ranjit and Gitesh without significant difference to each other and higher leaf folder population was recorded in Shraboni (9.89%) followed by Bahadur (9.67%), Bahadur Sub-1 (9.61%) and Swarna Sub-1 (8.47%) at vegetative stage which reached peak at reproductive stage during kharif season. The population of caseworm and whorl maggot was higher in vegetative stage and subsequently declined till the reproductive stage in kharif season. No caseworm population was observed during rabi season due to scanty rainfall. Spider was observed as the most prominent predator followed by coccinellid beetle in all the seven varieties during kharif and rabi season. The relative abundance of spider varied from 7.58 per cent to 9.65 per cent recording minimum population in Shraboni and maximum in the mega variety, Ranjit without significant difference with Gitesh and Ranjit Sub-1. Stem borer caused higher damage in comparison to other insect pests in both the season regardless of the varieties recorded higher in reproductive stage in rabi season as compared to that of other growth stages in both the season. Dead heart incidence was 21.71 per cent in the variety Shraboni that was higher than that of 6 Bahadur (20.76%) and Bahadur Sub-1 (20.83%) without significance difference, but it was significantly differed with stem borer incidence of other varieties being lower in Gitesh (7.45%) at reproductive stage during kharif season. The stem borer incidence was higher in rabi season as compared to kharif season in all the varieties and higher stem borer incidence was recorded in the variety Shraboni (22.43%) followed by Bahadur (21.56%) and Bahadur Sub-1 (21.39%) and lower stem borer incidence (10.39%) was observed in the variety Gitesh without significant difference in the varieties, Ranjit (11.56%) and Ranjit Sub-1 (11.37%) at reproductive stage in rabi season. The study on the effects of weather variables on insect pest incidence revealed that maximum temperature and morning relative humidity were the major weather variables that influenced the damage incidence of the rice insect pests during kharif season. Likewise, maximum temperature, morning relative humidity and bright sunshine hour greatly influenced almost all the major insect pest incidence in rice during rabi season. Since stem borer was found to be the most dominant insect pest throughout all the growth stages of rice both in kharif and rabi season, the biochemical profile was estimated in healthy and infested leaves, stems and seeds in the seven rice varieties against stem borer. It was revealed that total soluble sugar, reducing and non reducing sugar, soluble protein, crude protein and free amino acid contents increased in stem borer infested leaves, stems and seeds than those of healthy ones in all the seven varieties. The increase in sugars, proteins and free amino acid content was more pronounced at 60 DAT in healthy and borer infested leaves and stems and also in healthy and borer infested seeds, but it increased without significant difference between healthy and borer infested leaves and stems both at 30 DAT and 90 DAT in all the seven varieties. The total sugar content in healthy leaves was 15.57 mg /g to 19.73 mg /g which increased significantly from 20.46 mg /g to 26.95 mg/g in damaged leaves at 60 DAT as the increase was higher in Shraboni that was more damaged by stem borer and minimum in Gitesh with lower stem borer incidence. The phenol content in healthy stem increased significantly in infested stems of Ranjit Sub-1(1.54 to 2.13 mg/g), Ranjit (1.51 to 2.10 mg/g) , Gitesh (1.46 to 2.14 mg/g) and Swarna Sub-1 (1.08 to 1.43 mg/g) at 60 DAT after borer damage, but the phenol content increased without significant difference between healthy and infested stems in Shraboni (0.80 to 0.97 mg/g), Bahadur Sub-1(1.02 to 1.34 mg/g) and Bahadur (1.01 to 1.32 mg/g) with higher stem borer incidence. As all the biochemical components except phenol and tannin content increased in the varieties of higher stem borer incidence namely, Shraboni, Bahadur and 7 Bahadur Sub-1, but phenol and tannin content increased in the varieties of lower stem borer incidence, viz., Gitesh, Ranjit, Ranjit Sub-1 and Swarna Sub-1. Higher sugar and protein content with lower phenol and tannin content imparted resistance to the rice varieties viz., Gitesh, Ranjit and Ranjit Sub-1 against stem borer. The non- chemical approach using Beauveria bassiana, Pseudomonas florescence and neem products to manage stem borer in three better performed varieties viz., Ranjit, Ranjit Sub-1 and Gitesh revealed that dead heart incidence was 15.43 per cent, 16.68 per cent and 15.84 per cent respectively without significant difference before one day of treatment in non chemical, chemical and farmers‟ practice respectively at 45 DAT. The dead heart incidence drastically reduced both in chemical (6.19%) and organic treatment (7.23%) without significant difference at 65 DAT in Ranjit. The recorded grain yield was 5.13 t/ha in chemical treatment that was at par with 4.45 t/ha in non chemical treatment. The use of these biopesticides was found to be safer to the natural enemies as the spider and coccinellid beetle population in organic treatment (10.59 and 9.49 number/hill) was at par with farmers‟ practice (12.83 and 11.67 number/hill) respectively. Due to cryptic behavior and nocturnal habit, stem borer is very difficult to manage, therefore the present study will surely help in breeding program to develop a stem borer resistant rice variety and to predict the emergence of stem borer for preparedness at the earliest possible time and to manage the stem borer using non chemical products as a better alternative to replace the irrational use of synthetic chemicals for human safety and environmental protection.ThesisItem Open Access POPULATION DYNAMICS AND CROP LOSS ASSESSMENT OF MAJOR INSECT PESTS OF CUCUMBER (Cucumis sativus)(2022) Ganesh, Balaga Mohan; Saikia, D.K.Cucumber (Cucumis sativus L.2n = 14) is one of the widely cultivated summer vegetable crops from the gourd family of Cucurbitaceae which is native to India. The climatic conditions of northeast India especially Assam are highly conducive for reproduction of insects, and this region has been considered to be a biodiversity hotspot. Moreover, this region has huge potential for the production of vegetable crops especially cucurbits, but insect pests like fruit flies, pumpkin beetle and sucking pests are major limiting factors for successful cultivation of cucurbits like cucumber etc. Therefore, understanding population fluctuation in the field in relation to losses caused by insect pests are a function of their population dynamics which needs to be thoroughly studied. In view of above factors, an investigation on “Population Dynamics and Crop Loss Assessment of Major Insect Pests of Cucumber (Cucumis sativus)” was carried out at Horticultural Farm and RNA laboratory of Agricultural Biotechnology, Assam Agricultural University, Jorhat. The results showed that during 2019 -2021 summer season, the red pumpkin beetle first appeared on 24th April 2019 and 7th May 2020 with initial population of 4.51 and 2.23 beetles per plant, respectively. However, maximum beetle populations were recorded on 8thMay 2019 and 3rd July 2020 with 6.15 and 6.52 beetles per plant, respectively. Similarly, during 2019-2021, the fruit infestation by fruit fly was recorded first time on 13th June, 2019 and 26th June ,2020 with per cent fruit infestation of 10.24 per cent and 10.75 per cent, respectively. However, highest level of fruit infestation by fruit fly was observed on 25th July, 2019 and 8th August 2020 with 46.86 and 41.3 per cent fruit infestation, respectively. The data on relative abundance of different insects of cucumber during 2019-2021 revealed that the relative abundance of fruit fly species, Bactrocera dorsalis (62.27%) was the highest followed by B. tau (15.68%), B. cucurbitae (10.73%), Dacus longicornis (2.47%), Coccinella transversalis (2.45%), Aulacophora foveicollis (2.20%), Micrapsis discolor (1.56%), A. frontalis (1.16%), and Coccinella septumapunctata (1.08%). During 2019 and 2020, the Simpson-Index diversity showed highest value for fruit fly (0.97 and 0.94) followed by predacious coccinellid beetles (0.67 and 0.71) and red pumpkin beetle (0.55 and 0.64), respectively. Whereas, Shannon-Wiener index diversity (H’) during 2019 and 2020 observed highest in fruit fly (1.65 and 1.85) followed by predacious coccinellid beetles (1.15 and 1.05) and pumpkin beetle (0.68 and 0.85), respectively. The results of yield loss studies during 2019-2020 revealed that the per cent fruit infestation was highest in untreated control plot (30.73%) compared to treated plot (26.8%) with fruit yield of 1223.91 kg/ha and 2311.83 kg/ha, respectively. The yield loss in untreated plot was recorded as 1087.91 kg/ha with 47.05 per cent avoidable loss in yield. Whereas, per cent yield increase over control during 2019-2021 (summer season) was observed as 88.88 per cent. However, economic injury level (EIL) of fruit fly with respect to cucumber was determined as 15.27 and 10.40 per cent with per cent fruit loss of 0.743 and 0.745 during 2019 and 2020, respectively. The optimal phylogenetic tree of 10 fruit fly specimens collected from different locations grouped into two clusters (Cluster A and Cluster B) of two specimens out groups namely B. rubigina and D. longicornis with branch length of 0.0724. In cluster-A, highest genetic distance of 0.047 was recorded between B. rubigina and B. dorsalis. Similarly, in cluster-B the highest genetic distance of 0.0682 was recorded between D. longicornis, B.tau and B.cucurbitae collected from different locations.ThesisItem Open Access Bioecology and development of IPM module against fruit flies in cucurbits(2019-09) Mudoi, Abhilisa; Saikia, Dilip KumarFruit flies are the excellent candidates for studies of biodiversity, adaptability in changing climatic conditions and invasion to new areas because of their polyphagous nature, high reproductive potential, wide range of distribution and great economic importance as pests. Therefore, an extensive elaboration of fruit flies was carried out in five different districts under Upper, Central and Lower Brahmaputra Valley Zones of Assam to know the prevalence and diversity pattern of different fruit fly species of cucurbits. Five species of fruit flies viz., Bactrocera cucurbitae Coquillett, B. tau Walker, B. dorsalis Hendel, along with two new species viz., B. scutellaris Bezzi and Dacus longicornis Wiedemann were recorded from different districts of Assam. Out of the five districts, maximum number of 2492 individuals were observed to be trapped in cue lure in Darrang district. The species diversity index (1.285) and richness indices (0.393) of fruit fly was found to be highest in Michajan village of Sibsagar district, whereas the lowest species diversity index, (0.656) was in Dhepor village of Sibsagar district but the lowest richness indices (0.132) was observed in Khataniapara village of Darrang district. In respect of distribution pattern, the fruit flies had clumped distribution in all the five different districts under the present investigation. The morphometric parameters of fruit flies showed that the mean body length was the highest (11.846 ± 0.027mm) in female D. longicornis and lowest (5.631±0.053mm) in male of B. cucurbitae. In general, adult males were short-lived as compared to females, however, the adult longevity of female fruit fly in different cucurbits varied from 63.91 ± 1.16, 60.37±0.41, 49.82±0.50mm in respect of B. dorsalis, B. tau and B. cucurbitae against bitter gourd, bitter gourd and bottle gourd, respectively. Morphometrics of immatures stages revealed that the egg (1.26±0.02 × 0.43±0.02), larval (9.59±0.07 × 1.85±0.01) and pupal (5.82±0.01 × 2.46±0.02) size was highest in B. tau followed by B. cucurbitae with 0.88±0.01 × 0.18±0.01, 8.07±0.07 × 1.12±0.01, 5.21±0.03 × 2.22±0.02mm, respectively. It is imperative to obtain a baseline data on the seasonal occurrence pattern of fruit flies and the influence of abiotic factors on their activities in a particular ecosystem. Therefore, an experiment was carried out under field conditions at the Horticultural orchard, Department of Horticulture, Assam Agricultural University, Jorhat during 2017-18 and 2018-19 to find out a suitable eco-friendly management module against fruit flies of bitter gourd. Insect pests encountered with the crop revealed altogether seven species under three orders with four families viz., B. cucurbitae, B. dorsalis, B. tau, Aphis gossypii Glover, Epilachna vigintioctopunctata F., Aulacophora foevicollis Lucas and Monolepta signata Olivier which were registered as major pests of bitter gourd. Among the natural enemies, a total of sixteen species belonging to three orders and seven families were recorded. Twelve different pollinator species were also recorded during the study period associated with the crop. The seasonal incidence of fruit flies indicated a maximum of 189.90 and 179.60 number of fruit flies were trapped during April, 2017-18 and 2018-19, respectively. Among the different insect pests, the relative abundance of fruit fly, B. dorsalis was the highest with 73.65 in 2017-18 and 69.41 per cent in 2018-19 and the lowest was in case of A. foevicolis and A. gossypii, respectively with 1.69 and 2.65 per cent during the respective years. The correlation study with population build up of fruit fly showed a significant positive correlation with maximum and minimum temperature. As regards to fruit fly management strategies, module IV comprised of good agricultural practices, installation of cue lure @ 10/ ha, destruction of damage fruits, spray of neem based insecticides and spray of spinosad 45 SC @ 0.3 ml/L was found to be the best with 0.90 damaged fruits / m2, followed by module III (2.28 damaged fruits / m2) and module II (3.23 damaged fruits / m2). Similarly, module IV (1.36/ m2) and module III (2.46/ m2) was also found to be superior in suppressing the population of phytophagous beetle, E. vigintioctopunctata. In case of M. signata and A. foevocolis, module III (2.30,2.25) and module IV (1.00,1.18) was almost at par in reducing the population. The maximum yield of 97.43 q/ha with a benefit cost ratio of 2.26 was recorded in module IV, followed by next effective module III (83.93 q/ha) with a benefit cost ratio of 2.08. However, the cue lure barrix fly trap showed maximum efficacy related to trap index of 28.76 and the lowest was recorded in molasses trap with trap index of 21.79.ThesisItem Open Access ECOLOGICAL AND BIOCHEMICAL BASIS OF RESISTANCE AGAINST STEM BORER AND LEAF FOLDER OF AROMATIC RICE(2020-01) Ahmed, Shabrin Sultana; Saikia, D. K.The present investigation was carried out at Instructional Cum Research farm, Assam Agricultural University, Jorhat during kharif 2017 and 2018, respectively to generate a comprehensive information about screening of different aromatic rice varieties along with to determine the relationship between physio-morphic as well as biochemical properties of aromatic rice varieties against the incidence of stem borer and leaf folder and also to study diversity of major insect pests and their natural enemies in rice ecosystem. Varietal screening of eleven aromatic rice varieties revealed that during kharif 2017 and 2018, none of the varieties showed resistance to stem borer in active tillering stage,whereas Kola Joha (12.33%), Sofguti Joha (12.75%), Boga Joha (13.37%), Maniki Joha (13.70%), Keteki Joha(15.67%), Ronga Joha (17.60%) Kon Joha (18.38%), and Krishna Joha (20.37%) showed moderately resistance during vegetative stage.The variety Kon Joha (4.79%) and Maniki Joha(2.40%), however showed resistance during reproductive stage.In case of damaged leaf due to leaf folder infestation, almost all the aromatic rice varieties were proved to be resistant during the study period except check variety “Jaya”.Different physio-morphic characters of rice plant against leaf folder damage recorded significant positive correlation with width of leaf blade (r = 0.821** and r = 0.865**),whereas significant negative impact was with plant height (r = -0.939** and r = -0.778**).The per cent dead heart (DH) caused by stem borer exhibited significant positive correlation with stem diameter (r = 0.829** and r = 0.816**),but it showed significant negative correlation with plant height (r = -0.732** and r = -0.784**), number of leaves (r = -0.962** and r = -0.891**), number of trichomes (r = -0.860** and r = -0.870**), number of tillers (r = -0.806** and r = -0.739**),number of grains per panicle(r = -0.688* and r = -0.771*) and thousand grain weight (r = -0.650* and r = -0.570NS ), respectively. In case of per cent WEH, width of leaf blade(r = 0.608* and r =0 .678) had positive impact,but plant height (r = -0.606* and r = -0.598*)and number of leaves ( r = - 0 .655* and r = - 0.577*) showed significant negative relationship. Total of 6 species of odonates, 5 species of spider, 2 species of coccinellids, 3 species of lepidopteran, 1(one) species of each hemipteran, homopteran and coleopteran insect were recorded during the investigation period. As regards to diversity index, Sofguti Joha (1.59) showed the highest diversity index and Kola Joha (0.90) showed the highest species richness at vegetative stage, whereas the highest evenness (0.99) was found in Boga Joha at harvesting stage. In case of natural enemy complex, the highest diversity index of 2.50 and species richness (3.05) were recorded in Boga Joha at vegetative stage and the highest species evenness (0.99) was observed in Kola Joha at harvesting stage. Different sampling methods revealed the highest abundance of S. innotata (16.47%) in Boga Joha, Cnaphalocrocis medinalis (12.50%) and Dicladispa armigera (7.66%) in Sofguti Joha,whereas Leptocorisa acuta (24.61%) was appeared as the highest in Maniki Joha and Nephotettix nigropictus (50.0%) in Sofguti Joha. A total of 5 species of spider were recorded during the investigation period.The variety Maniki Joha supported more abundance of Oxyopes javanus (11.04%), Pardosa pseudoannulata (14.93%) and Tetragnatha maxillosa (9.74%), whereas Argiope anasuja (7.56%) in Boga Joha and Neoscona theisi (6.38%) in Sofguti Joha, respectively.The sub-order of odonata, viz., Zygoptera and Anisoptera had equal numbers of species (3 species each) during 2018.Data collected through different sampling methods showed the highest abundance of Brachythemis contaminate (14.89%), Crocothemis Servilia Servilia (10.11%) in Sofguti Joha,, Diplacodes nebulosa (7.30%) in Kola Joha, Aciagrion hisopa (12.98%) and Agriocnemis pygmaea (11.68%) in Maniki Joha and Agriocnemis pieris (10.27%)in Boga Joha. Two species of predators under order coleoptera viz., Coccinella tranversalis (F.), Micraspis discolor (F.) were found to be observed during the period of investigation. However, the highest abundance of C. transversalis was found in Kola Joha with 9.44 per cent and M. discolor with 8.10 per cent in Boga Joha. Among the tested biochemical parameters, Phenol (r = -0.985** and r = -0.834**), Ortho-dihydroxy phenol (r = -0.963** and r = -0.829**), Tannin (r = - 0.837** and r = 0.621*), Peroxidase (r = -0.937** and r = 0.871**) and Phenylalanine Ammonia Lyase ( r = -0.972** and r = -0.622*) exhibited negative significant impact with stem borer and leaf folder infestation. However, protein (r = 0.946**) showed positive significant correlation only with stem borer infestation. In terms of aroma, both Kola Joha and Koni Joha performed excellent in aroma having a score of 5 followed by Maniki Joha, Boga Joha and Bokul Joha with a score of 3.5-4. However, Keteki Joha, Krishna Joha, Kon Joha and Sofguti Joha produced medium aroma with a score of 2.5-3 and Ronga Joha produced very low aroma (score 2).As regards to yield, the highest yield was attributed by Kon Joha (2535.35 kg/ha) and the lowest yield of 1366.31kg/ha was obtained in Tulsi Bhog Joha.ThesisItem Open Access BIOECOLOGY AND MANAGEMENT OF Lepidiota mansueta Burmeister (COLEOPTERA: SCARABAEIDAE)(AAU, Jorhat, 2014) Pujari, Dwiban; Dr Badal BhattacharyyaField and laboratory experiments were carried out at Majuli river island and White grub laboratory, Assam Agricultural University, Jorhat to study the bioecology and management of Lepidiota mansueta (Coleoptera: Scarabaeidae) during 2011 to 2013. Experimental results confirmed the biennial life cycle of L. mansueta. The incubation period was found to be varied from 13-18 days with a mean of 15.80 ± 1.70 days. There were three larval instars. The duration of first and second instar were relatively shorter and it ranged from 38-42 (mean: 39.45±1.47 days) and 53-65 days (mean: 61.70 ± 3.53 days) respectively. The third instar grub showed prolonged duration which ranged from 532-556 days with a mean of 542.65 ± 7.60 days. The pupal duration was found to be varied from 26-28 days (mean: 28.60 ± 1.90 days). The total duration from egg to adult ranged from 666-702 days with a mean of 688.20 ± 9.84 days. The mean length and width of egg was 4.96 ± 0.03 and 3.93 ± 0.04 mm, respectively. The mean length and width of first, second and third instar grubs were 13.30 ± 0.95 and 2.47 ± 0.51, 24.10 ± 1.32 and 6.93 ± 0.74, 48.30 ± 1.62 and 10.30 ± 1.02 mm, respectively. The mean length and width of the pupae were found to be 32.60 ± 1.04 and 11.50 ± 0.68 mm respectively. Sexual dimorphism based on adult morphometrics revealed that females were significantly longer in body length (48.4 ± 1.03 mm) than males (43.4 ± 0.51 mm). Although the head plus thorax length of both sexes were identical, the abdomen was significantly longer in female (22.7 ± 0.89 mm) than in male (17.8 ± 0.43 mm). The length of the female alimentary canal (115.0 ± 0.12 mm) significantly differed from the male (94.0 ± 0.08 mm). The mean length of fore legs (18.0 ± 0.12 mm) and mid legs (23.0 ± 0.09 mm) were significantly longer in male than female (Foreleg: 17.2 ± 0.13 and mid leg: 22.1 ± 0.12 mm), whereas the hind legs were identical in both the two sexes. In field conditions, none of the plants were damaged by both sexes of the beetles soon after emergence from the ground. Host specificity test comprised of thirty different plant species conducted in laboratory conditions also revealed that adults of both sexes of L. mansueta were non- feeding. The alimentary canals of dissected adults did not show any food materials in their guts which clearly indicated the non-feeding nature of adults. Further, scanning electron microscopy images of mandibles and maxillae of both sexes of the beetles did not exhibit any dentations which indicate that the mandibles and maxillae were not fitted for phytophagy but probably used for digging of soil for burrowing. In field, the first and second instar grubs were observed from April-May and May-July during 2011 and 2012 respectively. The third instar grubs were noticed in soil throughout the sampling periods with a peak population (4.2 and 3.7 per cubic meter) during August, 2011 & 2012. Habitat selection by L. mansueta grubs studied in five selected ecosystems at Majuli revealed that grubs were significantly more abundant in grasslands which were situated near water sources (8.0, 6.5 & 6.0 nos./m3 during 2011, 2012 and 2013). In open grassland, the mean population of grubs was 4.6, 4.7 & 4.2 numbers per cubic meter during 2011, 2012 and 2013 respectively. Studies on abundance of L. mansueta grubs in grassland and cultivated lands showed significant preference for the soil depth of 0-10 and 11-20 cm. In grassland, grubs showed significant preference for the soil depths of 0-10 (3.18 ± 2.49) and 11-20 cm (1.48 ± 1.06). In cultivated field, the mean number of grubs recorded in 0-10 and 11-20 cm depths were 0.84 ± 0.62 and 0.96 ± 0.66 number, respectively. The grub population recorded in 0-10 and 11-20 cm were found to be at par with each other but significantly differ from 21-30 and 31-40 cm soil depths. Correlation studies between L. mansueta grubs and soil physico-chemical parameters revealed that among soil physical parameters, bulk density (r = -0.804) and sand content (r = -0.482) had significant negative correlations. Among the soil chemical parameters, soil organic matter content (r = 0.834), available nitrogen (r = 0.802) and soil microbial biomass carbon (r = 0.781) had significant positive correlations, while, available P2O5 (r = -0.466) had significant negative correlation on grub population. Multiple regression analysis between grub population and soil parameters revealed that 92.7 per cent grub abundance could be attributed due to the combined influence of soil physico-chemical parameters. The tuber damage caused by the grubs of L. mansueta recorded in potato varied from 22.20 to 30.84 per cent with a mean damage of 28.95 ±1.39 and 27.33 ± 3.14 per cent during 2012 and 2013, respectively. Plant damage in sugarcane ranged from 14.81 to 26.46 with mean damage of 19.25 ± 3.76 and 20.27 ± 1.38 per cent during 2012 and 2013, respectively. The plant damage in green gram and corm damage in colocasia found to be varied from 12.94 to 20.47 and 14.51 to 19.12 with mean damage of 16.02 ± 1.74 & 17.55 ± 1.49 and 17.05 ± 1.33 & 15.52 ± 0.82 during 2012 and 2013, respectively. Among the six insecticides tested for their effectiveness against L. mansueta grubs in potato, fipronil 5 SC @ 150 g a.i./ha recorded lowest per cent of tuber damage on weight basis (5.24 and 4.57%) and this treatment was found to be at par with fipronil 5 SC @ 100 g a.i./ha (5.91 and 5.09%), chlorpyriphos 20 EC @ 400 g a.i./ha (5.55 and 6.20%) and quinalphos 25 EC @ 400 g a.i./ha (6.14 and 6.72%) but significantly superior over rest of the insecticides. On number basis, fipronil 5SC @ 150 g a.i./ha registered lowest tuber damage (4.20%), and it was at par with chlorpyriphos 20 EC @ 400 g a.i./ha (5.25 %) and quinalphos 25 EC @ 400 g a.i./ha (5.66%) during 2012 and chlorpyriphos 20 EC @ 400 g a.i./ha (5.18%), fipronil 5SC @ 100 g a.i./ha (5.99%) and quinalphos 25 EC @ 400 g a.i./ha (6.43%) during 2013, but significantly superior over rest of the treatments. As regards to tuber yield, all the insecticidal treatments exhibited statistical parity except amamectin benzoate 5% SG @ 12.5 g a.i./ha. However, highest benefit cost ratio was recorded in chlorpyriphos 20 EC @ 400 g a.i./ha treated plots (2.50 and 2.62) followed by quinalphos 25 EC @ 400 g a.i./ha (2.23 and 1.85).