MSc.

The study entitled “Biology and management of the two-spotted spider mite, Tetranychus urticae Koch (Prostigmata: Tetranychidae) on okra [Abelmoschus esculentus (L.) Moench]” was undertaken at Department of Agricultural Entomology, College of Horticulture, Vellanikkara during 2012-13. The objectives of the study were to elucidate the biology of T. urticae on okra and to evaluate selected acaropathogenic fungi viz., Hirsutella thompsonii and Beauveria bassiana, botanicals viz., neem oil 2 per cent and NSKE 5 per cent, and new acaricide molecules viz., spiromesifen 240 SC, fenazaquin 10 EC and diafenthiuron 50 WP for their bioefficacy against T. urticae on okra.
The study on the biology of T. urticae was conducted in the laboratory during October- November, 2012 at 30 + 20C and 61.5 + 7 % RH following leaf disc method. The life cycle of T. urticae consisted of egg, larva, protonymph, deutonymph and adult. 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). Adult male was smaller in size, reddish green or light red in colour and pear shaped. Adult female was broader, bright reddish in colour and globular in shape with long setae over the body and legs. 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 post-oviposition 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 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.
Field studies were conducted to evaluate two acaropathogenic fungi, two botanicals and three new acaricide molecules along with a standard check and an untreated control against T. urticae on okra during two seasons viz., February – May, 2012 and November, 2012 – February, 2013. The new acaricide molecules diafenthiuron 50 WP @ 400 g a.i. ha-1 fenazaquin 10 EC @ 125 g a.i. ha-1 and spiromesifen 240 SC @ 100 g a.i. ha-1 were highly effective against T. urticae, bringing significant reduction in mite population. Among the botanicals evaluated, neem oil 2 per cent was found to be superior to NSKE 5 per cent during the second season though on par with each other during the first season of study. Among the acaropathogenic fungi, B. bassiana was found to perform better than H. thompsonii in terms of per cent reduction in mite and egg counts over untreated control. However due to lack of consistent results for the bioagents and botanicals further trials have to be conducted to obtain conclusive results.