Sudhansu Bhagawati

Aim:Studying the efficacy of novel insecticides against major insect pests of potato. Methodology: Two consecutive sprays were performed for six novel insecticides in potato and the per cent reduction of both sucking and foliage feeding insects as well as reduction in tuber damage by subterranean insects was calculated out. Additionally, residue of the most promising insecticide was also estimated using RP-HPLC to determine its safety. Results: Among the tested insecticides, Fipronil 40% + -1 Imidacloprid 40% WG @ 300g a.i. ha significantly reduced the incidence of aphids (97.61%), flea beetles (91.37%) and hadda beetles (95.83%) as well as registered lowest tuber damage on both weight and number basis (2.44 and 2.43%, respectively) resulting in a marked increase in marketable tuber yield (148.17 q -1 ha ) and economic return (2.33). Residue of imidacloprid and -1 fipronil in potato samples was found to be 0.1828 mg kg and -1 0.0093 mg kg , respectively, at the time of harvest, which was recorded below the Codex MRLvalue. Interpretation: The insecticidal formulation, i.e., Fipronil 40% + -1 Imidacloprid 40% WG when applied @ 300 g a.i. ha can effectively manage both aboveground and subterranean insect pests of potato due to its dual mode of action with a residue level below MRL values in tubers at harvest signifying a cost effective and environment friendly management option for the potato growers of Assam. Key words: Evaluation, Fipronil, Imidacloprid, Insect pests, Insecticide, Potato crop

Studies were undertaken to evaluate the efficacy of six insecticides having newer chemistry against termites infesting tea plantations in Assam, India during 2020-21 and 2021-22. All the tested insecticides viz., imidacloprid 600 FS @ 800ml/ ha, imidacloprid 17.8 SL @ 350 ml/ ha, fipronil 5 SC @ 2 L/ ha, imidacloprid 70 WG @ 160 g/ ha, clothianidin 50 WDG @ 250 g/ ha and chlorantraniliprole 18.5 SC @ 500 ml/ ha recorded significantly less per cent of both plant and portion of infestation as compared to the untreated plots at 30 and 60 days after application. Among the insecticides, application of clothianidin 50 WDG @ 250 g/ ha recorded significant reduction of termite infestation both in portion and plant basis at 30 (6.65 and 6.36%) and 60 (8.31 and 7.55%) days after treatment. After 60 days of application of clothianidin 50 WDG @ 250 g/ ha, 77.02% reduction of termite infestation was recorded over the control plots resulting in significant increase in the net profit. No residual effect was observed in the plucked tea leaves even after 7 days of application of clothianidin 50 WDG @ 250 g/ ha. Present investigation would help the tea growers concerning with termite prone areas to reduce the infestation without causing any harmful effect to the end users.

A study was conducted to explore nutritionally superior sericigenous insect species by examining their dietary sources. This research addresses the growing global demand for animal-based food sources to sustain the population and aims to mitigate nutritional deficiencies. The analysis carried out during the current study revealed that all the four sericigenous insects were highly nutrient-dense. Among them, Antheraea frithi demonstrated the most desirable nutritional qualities in terms of proximate composition, elemental content, antioxidant activity, and anti-nutritional properties. Since all four silkworm species exhibited elevated levels of nutritional constituents, they could potentially be used to play a significant role in enhancing human nutrition. The findings also highlighted promising and encouraging results regarding anti-nutritional factors and antioxidant activity. Protein extractions from silkworm pupae could be utilized in the food, cosmetic, and pharmaceutical industries.

Aim: Studying the influence of certain novel insecticides on soil faunal communities. Methodology: Soil micro and macroarthropods, total bacterial and fungal population as well as the key soil enzyme activities were studied prior to and after application of insecticides at every 15 days interval to establish their impact. Results: Prior to the application of insecticides, Hymenoptera was recorded to be the most dominant order (54.74%) among the soil macroarthropods followed by Coleoptera (13.68%) and Araneae (11.57%) whereas Collembola and Oribatida were recorded as soil microarthropods registering 64.72 and 35.28 per cent, respectively. All the insecticidal treatments recorded a significant reduction (p=0.05) in the soil macroarthropod, bacterial and fungal population as well as soil enzymatic activities up to 75 days of application indicating the detrimental effects of insecticides as compared to the untreated plots, which showed more stable habitats for the soil fauna. On the contrary, the insecticidal treatments did not exhibit any significant impact (p=0.05) on the population of soil microarthropods during the study period. Interpretation: Adoption of ecofriendly pest management practices relying on balance dose of insecticides with proper application methodologies may give insight in maintaining the ecological balance of soil biota in agroecosystems. Key words: Chlorantraniliprole, Collembola, Insecticides, Soil biota

The nutritive value of five edible aquatic insects of Assam—Hemipterans; water bug (Diplonychus rusticus Fabricius) family belostomatidae; giant water bug (Lethocerus indicus Lepeletier and Serville) family belostomatidae; water scorpion (Laccotrephes sp.) family nepidae, water stick (Ranatra sp.) family nepidae; Coleopterans diving beetle (Cybister sp.) family dytiscidae—based on their proximate and elemental composition, antioxidant and antinutritional properties were assessed by using standard methods of analysis. Analytical studies revealed that the selected aquatic insect species have high nutritive value and are rich sources of protein (50.03 to 57.67%) and other nutrients (fat, carbohydrate and crude fiber, etc.) along with superior energy contents (331.98 to 506.38 kJ/100 g). The aquatic insect species also contained appreciable amounts of major and trace dietary elements. Phenol and flavonoid contents reflect its high antioxidant activity (80.82 to 91.47% DPPH inhibition). Tannin (18.50 to 60.76 mg tannic acid equivalent/100 g), phytic acid (11.72 to 97.30 mg/100 g) and oxalic acid (2.93 to 5.34 mg/100 g) as antinutritional compounds were registered below the toxic level (0.52% or 520 mg/100 g). The present findings indicate that the selected aquatic insect species can be considered as ideal candidates for exploration as food and feed to ensure nutritional and livelihood security of this region.

Experiments were carried out in the farmer’s field at Jorhat during 2015-16 and 2016-17 to study the population dynamics of red ant Dorylus orientalis Westwood in potato crop. The incidence of D. orientalis was observed both under flood free/ and prone conditions in three villages each, during potato growing season. These data were correlated with weather factors. The effect on population buildup was studied with observations at fortnightly interval starting from 1^st fortnight of October to 2^nd fortnight of February through fixed plot surveys. The observations revealed that maximum incidence (36.5, 33.2 and 30.1; 35.2, 32.5 and 29.8/ pit) was observed in Charaibahi, Karangia and Hokai Khangia villages, respectively during the 1^st fortnight of January. In contrast, in the flood prone villages, incidence was observed to be negligible. Correlation coefficients of incidence with weather factors revealed that minimum temperature, soil temperature (morning and evening) and evaporation rate show a significantly negative correlation; whereas relative humidity (RH) (morning and evening) exhibited significant positive correlation in flood free villages. In flood prone villages minimum temperature as well as morning soil temperature showed significant negative correlation (2015-16); in contrast, in flood prone villages, RH (morning and evening) showed significant positive correlation (2016-17).

Field experiments were conducted at Charaibahi village, Jorhat, Assam during 2015-17 to evaluate six ecofriendly IPM modules against red ants Dorylus orientalis Westwood in potato. Among the modules evaluated, Module-II (pre sowing treatment of mustard oil cake @ 150 kg/ ha+ wood ash 150 kg/ ha+ panchagavya @ 3% and soil drenching with neem oil @ 5 ml/ lit after 1^st and 2^nd earthing up (25 and 60 DAS) recorded the lowest tuber damage both in weight (8.65%) and number (10.70%) basis and found at par with the recommended package of practices (RPP) (application of malathion 5% dust @ 40 kg/ ha+ mustard oil cake @ 150 kg/ ha in the soil after 1^st and 2^nd earthing up) recording 8.18 and 10.20% tuber damage, respectively. The same module also recorded highest tuber yield (119.37 q/ ha) which was at par with the RPP (120.12 q/ ha). The maximum benefit cost ratio (1.41) was recorded in RPP followed by Module-II (1.33) and Module-VI (1.26). The untreated control plot registered a very high level of tuber damage (25.93 and 28.70 on weight and number basis, respectively) having maximum population of red ants (3.95 numbers/ m² ) with a tuber yield of 89.91 q/ ha.

Land use change has a great impact in determining the diversity patterns of soil fauna. Adoption of any land use pattern significantly affects the soil structure and its physico-chemical characteristics, which often leads to the loss of biodiversity. Considering the collembolans as the key organism in the indicator shopping basket of soil environment, the response of Collembola communities under three different land uses represented by forest, vegetable and tea ecosystems was studied. Collembolans were sampled at monthly intervals using Tullgren funnel and identified by standard taxonomic keys. Diversity analysis and soil chemo-edaphic factors were studied to establish the impact of different land uses on Collembola communities. Five genera of Collembola viz., Cyphoderus, Entomobrya, Isotoma, Folsomia and Hypogastrura were recorded from the forest ecosystem whereas Folsomia was completely absent in vegetable ecosystem and the tea ecosystem soil was devoid of both Folsomia and Hypogastrura. Seasonal diversity and density of Collembola were recorded to be higher in the forest ecosystem indicating the presence of relatively stable habitats as compared to vegetable and tea ecosystems showing relatively disturbed habitats. Correlation studies between different chemo-edaphic factors and collembolan population revealed that the moisture and organic carbon content of soil had significant positive correlation during all the four seasons in all the ecosystems studied. Higher adoption of mechanical and chemo-centric agriculture depletes the available resources of the soil and makes it less habitable and conducive for the growth and sustenance of collembolans in vegetable and tea ecosystem as compared to forest. Appropriate landscape planning, land management strategies and developing proper methods of land use practices may pave the way for the improvement of collembolan diversity at landscape level.

Aim: To investigate the influence of soil physico-chemical properties on diversity and density of Collembola in an undisturbed fallow land ecosystem. Methodology: Soil sampling was done at monthly intervals to explore the diversity, density and seasonal variation patterns of collembolan population in a fallow land ecosystem during March, 2015 to February, 2016. Collembolans were sampled using Tullgren funnel and identified by standard taxonomic keys. Finally, correlation studies were conducted to assess the influence of different soil physico-chemical properties on diversity and density of collembolans. Results: Five species of Collembola (Cyphoderus sp., Entomobrya sp., Isotoma sp., Folsomia sp. and Hypogastrura sp.) belonging to 4 families (Cyphoderidae, Entomobryidae, Isotomidae and Hypogastruridae) were identified. Cyphoderus sp. was recorded to be the most abundant species contributing 44.29 percent of population. Analysis of different diversity indices revealed higher diversity of collembolans during summer, indicating the presence of relatively stable habitats as compared to other seasons. Summer season also recorded highest density of Collembola. During all the seasons studied, a strong significant positive correlation (P

Field studies were conducted to know the relationship between different tillage practices and the existence as well as depth of beetle holes of Lepidiota mansueta in some selected endemic villages. The results revealed that the maximum number of beetle holes (13.91–15.94/sq.m.) were recorded in the areas where no tillage operations were carried out and kept as uncultivated land followed by conventional tillage by bullocks (8.64–9.67/sq.m.) and tillage operation done by power tillers (4.59–5.69/sq.m.). Minimum number of holes (3.16–3.67/sq.m.) was found in areas where tillage operation was performed by the tractors. There was no significant differences observed (P = 0.05) in terms of depth of beetle holes in soil irrespective of the tillage operations conducted.