Emergence and Incidence of Coffee White Stemborer, Xylotrechus quadripes Chevrolat, 1863 (Coleoptera: Cerambycidae), under Different Rainfall Regimes across the Coffee-growing Regions of Karnataka, India

The coffee white stem borer (CWSB), Xyloterchus quadripes Chevrolat, 1863 (Coleoptera: Cerambycidae) is one of the most destructive pests of arabica coffee in India. As coffee cultivation in India is mostly confined to the hilly tracts of the Western Ghats of the southern states and it is mainly grown in Kodagu, Chikmagalur and Hassan districts of Karnataka with varying rainfall patterns ranging from more than 3000 mm to less than 1000 mm. The study of the incidence of WSB and emergence of adults in relation to local weather conditions in the estates at different rainfall patterns in Karnataka [High(<2500mm), Medium (2000 to 1000mm) and low(<1000mm) rainfall areas] for two years (2016 and 2017). The emergence data and local weather parameters viz rainfall, relative humidity and temperature were correlated with adult emergence. The results indicated that the emergence of CWSB during the years 2016 and 2017 exhibited a significant positive correlation with maximum temperature and minimum temperature. While beetle emergence was negatively correlated with the quantity of rainfall and relative humidity across the six locations. From these observations, it is evident that the beetles required a higher temperature for their emergence and peak beetle emergence occurred during the middle of November in the winter flight season and during the end of April and the first fortnight of May in the summer flight periods. Multiple linear regression analysis revealed that measured abiotic factors have significant effects on emergence of CWSB adults confirming results of correlation analysis. During the same period 2016-17, coffee plantations were surveyed randomly in all the three rainfall regimes to know the influence of annual rainfall on incidence of CWSB and the percent incidence was 10.81% at rainfall <1000, 7.67% at medium rainfall and 6.16% at high rainfall areas and was non-significant across rainfall regimes.