The insect gut has been the house of many taxonomically and physiologically diverse groups of microbial colonizers as symbionts and commensals, which are evolving to support the physiological requirement of insects. Lepidoptera is one of the important family of class hexapoda, comprising agriculture insect pest Spodoptera litura and Spilosoma obliqua. Information on gut microbiota and their functional role in these insects was meager to elucidate the wide-ranging survivalist mechanisms. In this context, we analyzed the composition, diversity and functional role of gut bacteria in S. litura and S. obliqua collected from soybean and sunflower crops, respectively, using Next Generation Sequencing of 16S rRNA. A total of 3427 and 206 Operation Taxonomic Units (OTUs) were identified in S. litura and S. obliqua gut metagenome, respectively. Highest number of sequences were annotated to unclassified bacteria (34%), followed by Proteobacteria (27%), and Chlorobi (14%) in S. litura, while S. obliqua has significant representation of Firmicutes (48%), followed by Bacteroidetes (20%), and unclassified bacteria (11%). Functionality of both metagenomes revealed, high abundance of ammonia oxidizers (20.1 58.0%) followed by relative abundance of detoxifying processes - dehalogenation (17.4-41.2%) and aromatic hydrocarbons degradation (1.1-3.1%). This study highlights the significance of the inherent microbiome of two defoliators in shaping the metagenome for nutrition and detoxifying the chemical molecules, and opens an avenue for exploring role of insect gut bacteria in host selection, metabolic endurance of insecticides and synergistic or agonistic mechanisms inside gut of insects feeding on insect-resistant biotech crops.

Gram pod borer, Helicoverpa armigera is a serious insect pest of pigeonpea and chickpea crops, responsible for huge economic losses. Timely forecasting and subsequent sensible management practices of H. armigera would save the crops from economic damage. In the present study, H. armigera larval incidence data was recorded from sixteen pigeonpea and chickpea growing locations (Maharashtra, India) for three seasons (2015, 2016 and 2017). Observed accumulated GDD (from 40 SMW to 7 SMW) revealed, H. armigera completed one generation in 29 days to develop 4 generations across the locations and seasons. After accumulating 86GDD (40 SMW) and 62 GDD (43 SMW), larval ‘biofix’ (initial incidence of larvae) was started in pigeonpea and chickpea, respectively. Logistic regression model estimated accumulated GDD required by H. armigera larvae to reach ETL in pigeonpea (629 GDD) and chickpea (378 GDD), which was same as observed accumulated GDD. Statistical criteria viz., Adjusted r2, AIC and BIC projected logistic regression model as a better performer in most cases. The geographically unique models developed based on biofix and accumulated GDD in this study can be used for timely advisories and sustainable management of H. armigera in pigeonpea and chickpea crops after field validation.

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