Seasonal Incidence of Diaphorina citri Kuwayama in Assam Lemon and Its Relationship with Weather Factors in Sub-Himalayan Plains of West Bengal

Abstract

Seasonal incidence of citrus psylla, Diaphorina citri Kuwayama was studied in Assam Lemon ( Citrus limon L. Burm) in two consecutive years in sub-Himalayan plains (terai zone) of West Bengal (India). The psyllids appeared with the arrival of new flush which occurred three times a year, the first during January last to early February (4 th -5 th SW), second during April-May (17 th - 18 th SW) and the third during September (37 th -38 th SW). Three peaks were recorded—one at 11 th SW (6.11 psyllids/shoot), the second at 21 st SW (7.50 psyllids/shoot) and the third peak at 43 rd SW (5.06 psyllids/shoot). The second peak recorded the highest psyllid population. The psylla were active throughout the whole year except during the cold winter period when their population was either low or absent. Temperature showed a positive association with psyllid population (r = 0.304 for T Max and r = 0.182 for T Min ) while RH% (r = −0.200 for RH Mor and r = −0.200 for RH Evn ) and rainfall had a negative correlation (r = −0.013). During the 1st peak population (11 th SW) the average temperature, RH% and rainfall were 30.82˚C (T Max ) and 16.68˚C (T Min ), 55.36% (RH Mor ) and 62.72% (RH Evn ) and nought respectively; while the corresponding values were 33.43˚C (T Max ) and 24.29˚C (T Min ), 76.43% (RH Mor ) and 75% (RH Evn ) and 7.85 mm respectively during the 2nd peak (21 st SW). Likewise, at the 3 rd peak (43 rd SW), the respective values were 30.22˚C and 19.07˚C (T Max and T Min , respectively), 80% and 76.79% (RH Mor and RH Evn , respectively) and zero mm respectively.