MOVEMENT OF WOOLLY APPLE APHID (ERIOSOMA-LANIGERUM) (HOMOPTERA, PEMPHIGIDAE) ON APPLE (MALUS-PUMILA) PLANT IN RELATION TO WEATHER PARAMETERS

A field study was carried out during 1991 and 1992 on 20-year-old 'Roy al Delicious' apple (Malus pumila Mill.) trees at Mashobra, to investi gate the movement of woolly apple aphid [Eriosoma lanigerum (Hausmann) ]. The movement was confined to the first-instar nymphs and continued throughout the year except in severe winter at 3.8 degrees C mean temp erature (-2.5 to 9.3 degrees C). The movement was significantly higher (65%) from root to shoot zone than from shoot to root zone (35%). Amb ient temperature (> 10.3 degrees C) and soil temperature (> 11.5 degre es C) triggered the aphid movement toward both the zones. Increase in ambient temperature from 13.2 to 26 degrees C favoured maximum movemen t unless interrupted by other factors. Two simultaneous upward and dow nward movement peaks were recorded each year, first during mid-June an d second during October-November. Rainfall > 72 mm in a fortnight affe cted 57% upward and 71% downward aphid movement Subsequent rainfall re sulted in 99.8-100% check in nymphal movement even in most favourable temperature range (13.2-25.9 degrees C). The net correlation between m ovement and mean maximum temperature was positive and significant, whe reas it was non-significant for mean minimum temperature and rainfall. Multiple regression analysis revealed 22.69 and 52.96% variation in u pward and 23.74 and 47.45% in downward nymphal movement due to weather parameters in 1991 and 1992 respectively.