Biology of Two-spotted Spider Mite Tetranychus urticae Koch (Acari: Tetranychidae) on Okra

The studies on the development and life history traits of T. urticae were conducted in the Acarology laboratory following leaf disc method. The life cycle of T. urticae Koch consisted of egg, larva, protonymph, deutonymph and adult stages. The immature stages were followed by short quiescent intervals called nymhochrysalis, deutochrysalis and teleiochrysalis. The mite recorded an incubation period of 2.92 days. Larval period of 0.83 and 1.19 days, protonymphal period of 0.36 and 0.58 days and deutonymphal period of 0.67 and 0.29 days were recorded respectively in male and female T. urticae. The total developmental period from egg to adult emergence was shorter for male (6.73 days) compared to female (7.52 days). Mating took place immediately after the emergence of the female. T. urticae exhibited both sexual and parthenogenetic reproduction. Mated female's progeny consisted of both males and females in the ratio 1:5.8, whereas unmated female produced 100 per cent males. Pre-oviposition, oviposition and postoviposition periods lasted for 0.58, 9 and 4 days and 0.58, 11 and 4.5 days respectively in mated and unmated female. Mated and unmated females on an average produced 108 and 77 eggs. The adult mite recorded longevity of 12, 12.5 and 17 days for male, mated female and unmated female respectively. The shorter developmental period and minute size of T. urticae coupled with high fecundity would help the mite build up population very fast and successfully complete several generations in a crop season attaining the status of major pest.