Assessing the impact of micro climate on population dynamics of onion thrips in gangetic west bengal

Abstract

Onion thrips [Thrips tabaci L. (Thysanoptera: Thripidae)], is the most important poly-phagous pest in onion crop as it significantly affects the productivity and marketability of onion bulbs globally. However, spatial and temporal variability in the infestation of onion thrips is highly variable and generally inconsistent with environmental conditions, which regulate its development and reproduction. In fact, thrips population gets affected due to varying weather pattern under different agro-climatic conditions. However, the information on seasonal thrips population density and their relationship with microclimate, is scarce in New Alluvial Agro Climatic Zone of West Bengal under varying management practices. In view of the above, the present study was conducted at Research Farm, Gayespur of Bidhan Chandra Krishi Viswavidyalaya, Kalyani, Nadia, West Bengal during kharif seasons of 2014 and 2015, and rabi seasons of 2014-15 and 2015-16. The results revealed that temperature and relative humidity within the onion crop canopy were higher at early growth stages for all treatments. In contrast, incident photosynthetic active radiation (PAR) and reflected PAR were observed to be maximum during reproductive phases and minimum during vegetative phases of the crop.Soil temperature in the cropped field, followed a consistently upward trend during active vegetative period, followed by drastic reduction at the initiation of reproductive phases. No abiotic stress was observed for kharif onion. During rabi season, planting date was found to be significantly influencing the microclimatic environment of onion crop However, spacing schedules exerted less influence on behaviour of microclimate. Treatment combinations of P4S1(22nd November, 15cm×10cm)and P4S2(22nd November, 20cm×15cm), shortened the onion maturity by 20 days. Canopy temperature and relative humidity exhibited higher values, during later part of onion growth. Results on temporal dynamics of thrips population in kharif season showed that earliest incidence of thrips was recorded at 65 DAP and 58 DAP in the crop planted on 14th August and 21st August, respectively and at 51 DAP for both P3 (28th August) and P4 (4th September) planted crops. In case of rabi season, it was found that first incidence of thrips started at 40 DAP, which went on increasing till 68 DAP for each treatment. Moreover, declining trend was also noted from 75 DAP onwards. Increase in thrips population was observed to be associated with changes in cumulative degree days during active reproductive phase. Significant correlations of thrips population with canopy temperature, canopy humidity and soil temperature were observed.