Influence of crop phenology on population dynamics of aphid, Uroleucon compositae Theobald and its predators.
Field experiment was conducted during 2001-02 rabi to study the influence of crop phenology and meteorological factors on the incidence of aphid (Uroleucon compositae Theobald) on safflower (Carthamus tinctorius L). The aphid appeared in the safflower field in 51st standard week during 2007, i.e., December 3rd week when the crop was seven weeks old. Later the population gradually increased up to 2nd standard week of 2002 and reached the peak (118.4 aphids/5 cm apical twig in 3rd standard week). The mean maximum temperature of 28-30°C and minimum temperature of 13-16°C and relative humidity of 83.4% were found most conducive for aphid multiplication. The peak aphid population was observed at 83.4 per cent relative humidity. Lower relative humidity of 74.2 per cent and increase in temperature during first week of February set in a decline in aphid population. The predators C. septempunctata, M. sexmaculatus and C. carnea were found to appear one week after the appearance of U. compositae on safflower. The predators population peaked during third week of January when aphids were also maximum in number. Mean maximum temperature coupled with relative humidity had significant negative correlation (r=-0.63) on aphid population. But coccinellids and chrysopids had highly significant and positive correlation (r=0.97 and r=0.96, respectively) with the aphids. The partial regression equations showed a highly significant negative impact of mean minimum temperature and positive relation of coccinellids and chrysopids with aphids.