Effect of abiotic stresses on population build up of Tetranychus urticae Koch and its predator, Stethorus punctillum Weise on okra.

摘要

Studies on seasonal incidence of Tetranychus urticae, a two spotted spider mite and its coccinellid predator, Stethorus punctillum were carried out in summer and kharif seasons of 2006-2007 on okra. Mite T. urticae population showed two peaks on okra, during first week of June (47.1, 48.8, 46.0 and 8.5, 13.5 & 9.3 mites cm2 leaf from ventral surface and dorsal surface of the leaves of three strata, respectively) and during first week of August (36.8, 45.9, 21.4 & 17.9, 21.5, 7.3 mites cm2 leaf from ventral and dorsal surface of the leaves of three strata, respectively). Predatory beetle, S. punctillum also showed two peaks; first in the fifth week of July (1.0, 1.3, 0.2 on ventral & 0.3, 0.8, 0.0 beetles/leaf on dorsal surface of the three strata, respectively) and second in the first week of August (0.3, 1.2, 0.0 on ventral & 0.4, 0.7, 0.0 beetles/leaf on dorsal surface of the leaves of three strata, respectively) which coincided with peak in T. urticae population. Strata wise, middle strata harboured significantly more number of mites and beetles followed by top and bottom strata. Among abiotic factors, maximum and minimum temperature and relative humidity played a significant role in the population build up of T. urticae.