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Mites have emerged as serious pest of rice, particularly in South India in the recent years. The rice leaf mite, Oligonychus oryzae Hirst (Acari: Tetranychidae) is reported to cause a reduction in yield of 25 per cent in rice. Sporadic incidence of the leaf mite has been reported recently from many rice growing tracts of Kerala as well. Yet, hardly any study has been conducted either on biology or management of this important pest.
The present study entitled “Biology and management of the rice leaf mite, Oligonychus oryzae (Acari: Tetranychidae) was undertaken at Department of Agricultural Entomology, College of Horticulture, Vellanikkara during 2014-15. The objectives of the study were to elucidate the biology of O. oryzae on rice and to evaluate four new acaricide molecules namely, spiromesifen 240 SC, fenazaquin 10 EC, fenpyroximate 5 SC, propargite 57 SC, two botanicals (neem oil 2 per cent and azadirachtin 0.005 per cent) and wettable sulphur 80 WP against O. oryzae on rice.
The study on the biology of O. oryzae was conducted in the Acarology laboratory during July-August, 2014 at 27+ 3 0 C and 70.2 + 7 per cent RH, following leaf bit method. The life cycle of O. oryzae 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 3.80 days. Larval period of 1.37 and 1.40 days, protonymphal period of 0.91 and 1.04 days and deutonymphal period of 0.98 and 1.30 days were recorded in males and females of O. oryzae respectively. The total development period from egg to


adult was shorter for male (9.87 days) as compared to female (10.47 days). O. oryzae exhibited both sexual and parthenogenetic reproduction. Mated female’s progeny consisted of both males and females in the ratio 1: 3, whereas, unmated female produced only males. Pre-oviposition, oviposition and post-oviposition periods lasted for 0.89, 6.27 and 2.08 days in case of mated female, and 1.02, 7.31 and 2.12 days in unmated female respectively. Mated and unmated females on an average produced 21 and 17 eggs respectively. The adult mite recorded longevity of 8.00, 10.34 and 12.1 days for male, mated female and unmated female, respectively.
The new acaricide molecules namely, fenazaquin 10 EC, spiromesifen 240 SC and propargite 57 SC evaluated in the laboratory resulted in significantly higher mortality of eggs and gravid females, 72 h after treatment application.
In the pot culture experiment, all the four novel acaricide molecules tested, namely fenazaquin, spiromesifen, fenpyroximate and propargite succeeded in reducing the population of O. oryzae significantly. Efficacy of these molecules in reducing the mite population was pronounced from 3 rd day after spray application. Wettable sulphur also showed high efficacy against O. oryzae and 14 days after treatment application, its efficacy was on par with novel acaricide molecules. The botanicals tested significantly reduced mite population over untreated control, though were found to be inferior to all other treatments.
The study has for the first time, documented the biology of O. oryzae in Kerala, which could form the basis for future investigation into ecological and management aspects of the mite. It has also succeeded in identifying a number of novel molecules for further, field level evaluation.