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The red flour beetle, Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) is one of the major destructive pests to stored milled products. It has developed resistance to chemical fumigants. Therefore, finding an eco-friendly biofumigant for the management of the pest is of great importance. The main aim of this study was to evaluate the insecticidal efficacy of essential oil from Cymbopogon flexuosus (lemongrass), Cymbopogon winterianus (citronella), and Cymbopogon martini (palmarosa) against T. castaneum and its chemical composition. GC–MS analysis was conducted and results showed that the essential oils of C. flexuosus, C. winterianus and C. martini are rich in citral, neral, cironellol, D-lemonene, geraniol and geranyl acetate respectively. The essential oils from C. flexuosus, C. winterianus and C. martini had a very strong repellent activity to adults of T. castaneum and were significantly repellent at 1.41 µL/cm2. The essential oil of C. flexuosus had a high fumigant activity against adults of T. castaneum with LC50 values of 27.1 and 4.23 µL/L after 24 and 48 h exposure. Furthermore, essential oils of C. winterianus had a high contact toxicity to T. castaneum with LD50 values of 2.1 and 1.5 µg/L after 24 and 48 h exposure, followed by 2.5 and 1.6 µg/L of C. martini and 4.09 and 2.07 µg/L of C. flexuosus after 24 and 48 h exposure respectively. The results show that essential oils extracted from the Cymbopogon species are natural insecticides and can be used as an efficient management tool against T. castaneum.

The essential oils extracted from Cymbopogon flexuosus, Cymbopogon winterianus, Cymbopogon martini were analyzed by trapping the volatile organic compounds using solid-phase microextraction-gas chromatography-mass spectrometry and evaluated their antifungal activity against plant fungal pathogens like Fusarium oxysporum f. sp. cepa (Hypocreales: Nectriaceae) and Sclerotium oryzae Cattan (Magnaporthales: Magnaporthaceae). The major volatile organic constituents of C. flexuosus-citral (22.94%), neral (19.88%), camphene (8.37%), cyclohexene, 1-methyl-5-(1-methylethenyl-(R) (5.75%); C. winterianus-citronellal (42.47%), D-limonene (10.86%), geraniol (9.44%), citronellol (6.25%); C. martini-geraniol (43.80%), a-ocimene (10.75%), geranyl acetate (6.35%), 2,6-octadienal, 3,7-dimethyl-(E) (5.83%), were found in concentrations higher than 5.0% (calculated as % peak area of GC-MS analysis using a nonpolar column). In addition, the antifungal tests were also demonstrated that the essential oil of C. flexuosus C. winterianus and C. martini have excellent inhibitory effect against S. oryzae and F. oxysporum. The IC50 values of essential oils from C. flexuosus, C. winterianus and C. martini against at S. oryzae and F. oxysporum were 0.42, 0.41, 1.99 and 0.73, 2.02, 2.01 μL/plate respectively. The significant aroma may be the results of combined 30 volatile organic compounds from essential oils of Cymbopogon species which could be used as safe biocontrol agents to prevent stored product commodities from fungal pathogens.

Growth ring study of Pinus kesiya (khasi pine) growing in sub-tropical forest in Manipur, northeast India was performed to understand climate signatures in ring widths and intra-annual density fluctuations. The growth rings in khasi pine (Pinus kesiya Royle ex Gordon) growing in sub-tropical Reserve Forest in Imphal, Manipur, northeast India were analysed to understand environmental signals present in ring-width series and intra-annual density fluctuations (IADFs). For this the growth ring sequences in increment core samples collected from 28 trees were precisely dated and a ring-width chronology spanning AD 1958–2014 developed. The correlation analyses between ring-width chronology and weather data of Imphal revealed that a cool April–May–June favour tree growth. The wood anatomical features of growth rings revealed the occurrence of IADFs in early- and latewoods. The IADFs in earlywood were found to be associated with reduced precipitation in months from April to July. However, the wetter conditions in late growing season, especially August/September triggered the formation of IADFs in latewood. Our findings endorse that the IADF chronologies of khasi pine could emerge as an important proxy of summer monsoon rainfall in long-term perspective in data scarce region of northeast India.

Forest fires are known to significantly alter soil nutrient availability. The study investigated the post-fire nutrient availability in the sub-tropical forest ecosystem of Koubru Hills, Manipur (North-East India). The forested ecosystem was disturbed by forest wildfire in January 2010.To study the fire effect, collection of burned and unburned soil samples from three soil depths (0-5, 5-10 and 10-15 cm) was started approximately three months after the fire event and continued at monthly intervals for a period of one year. The collected soil samples were analyzed for soil organic carbon (SOC), NH4+-N, Bray-extractable phosphorus, available potassium and micronutrients such as Fe, Cu, Mn and Zn. Results of the ANOVA test showed significant reduction in the SOC, NH4+-N and available K contents of the surface (0-5 cm) and sub-surface (5–10 and 10-15 cm) soil layers of the burned area. However, significant increases in the Bray-extractable phosphorus were observed in all the three soil depths studied. With respect to the effect of forest fire on soil micronutrient availability, results are contradictory. The available Fe depleted in all the three soil depths, whilst the available Cu declined in the 0-5 cm but increased in the 10-15 cm soil layer. The available Cu content of the 5-10 cm soil layer did not vary between the burned and unburned areas. While no significant effect of fire was observed on the available Mn contents of the 0-5 and 10-15 cm soil layers, there was a significant post-fire decrease in the Mn availability of the 5-10 cm soil layer of the burned area compared with the unburned area. Forest fire also resulted in a significant loss of the available Zn from the 0-5 and 5-10 cm soil layers of the burned area but in the 10-15 cm soil layer, no significant variation was observed between the burned and unburned areas.