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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.

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.