Population dynamics of two spotted spider mite (Tetranychus urticae Koch) on cucumber in relation to weather parameters under protected environment

Population dynamics of two spotted spider mite, Tetranychus urticae Koch on parthenocarpic cucumber crop grown under naturally ventilated polyhouse was studied by releasing 2, 4, 8 and 16 adult female mites/ leaf on 4, 6 and 8 weeks, after transplanting (WAT) with the infestation initiated 4-WAT, the mite population increased gradually up to 21 days after release (DAR). The population increased significantly 28-DAR onwards till final harvesting of the crop (70 days after release) with the resultant population levels of 209.8, 225.7, 314.7 and 351.4 mites/ leaf at release levels of 2, 4, 8 and 16 mites/ leaf. Whereas, mites released 6 and 8-WAT, resulted in population to increase significantly at all observational dates. Cumulative mite days worked out on the basis of population buildup at different release levels, resulted in higher values (3809-8598) for infestation initiated 4-WAT in different release levels. However, it ranged between 1743-7062 and 1250-5634 for the infestation initiated 6- and 8-WAT. Relationship worked out between population levels and weather parameters revealed the minimum temperature, maximum and minimum relative humidity to influence the population buildup of T. urticae positively, significant for infestation initiated 4 and 6-WAT only. Whereas, maximum temperature influenced the population negatively, but the influence being non-significant. Step-wise regression analysis of population buildup of T. urticae revealed the minimum temperature to be the lone abiotic factor in determining abundance of two spotted spider mite and influenced the buildup of the mite to the extent of 75 and 87 per cent for the infestation initiated 4- and 6-WAT, respectively.