Species complex, biology and management of thrips on grapes, cv. Bangalore Blue

Abstract

The investigations on the thrips species complex, biology & seasonal incidence of S. dorsalis in relation to weather climate parameters; extent of damage and management chemical control of S. dorsalis were made from 2001-2002 for two seasons one being carried out(winter and summer) in the field and laboratory during 2000-01. During survey in South India five species of thrips belonging to three different families were recorded. Of these, four are new records for India. This study has revealed two families viz., Aeolothripidae and Phlaeothripidae as having new records of species that are associated with S. dorsalis. This is a significant addition to the known species complex of thrips in Karnataka and India. No inter vine variation was observed in the thrips distribution. However, the density of thrips differed between the different crop stages. The larvae and adults of S. dorsalis caused damage to all stages of the crop. The insect pierced the leaves, petioles and berries and sucked the sap resulting in silvery white scorch patches on the leaves and scars on berries, Under severe infestations, the leaves withered and ultimately fell down. Further, scarring and cracks on fruit surface was exhibited. The affected mature berries turn ugly and severely affected bunches are unfit for marketing. Phenology of the crop played a significant role in determining the level of thrips infestation. The density of S. dorsalis and other species of thrips reached the peak level (12.92 and 0.74 during winter) at 30-40 days after pruning, when the crop was in tender leaf stage and flowering initiated. Similarly, in summer, peak populations of S. dorsalis (16/49) and other species of thrips(0.80) coincided with tender leaf and flowering stage. As far as the effect of crop phenology on thrips density, tender leaves were found to have positive effect. Fully matured leaves, small, medium and large size fruits were found to have negative effect. The female laid eggs singly in the tissues mostly on the tender pods, occasionally in older pods. The egg was kidney or oval shaped and glossy white in colour. On an average it took 14.35 + 3.18 days to complete the life cycle. On an average each stage viz., egg, first, second instar larva, prepupa and pupa lasted for 3.97 + 1.58 + 0.42 days, 2.92 + 0.55 days, 1.03 + 0.28 days and 3.88 + 0.46 days, respectively. The oviposition started after a period of 1.5 + 0.48 days and lasted for 1.89 + 0.65 days. Female laid on an average 2.1 + 0.94 eggs per day and lived for 4.48 + 1.03 days. The incidence of S. dorsalis prevailed throughout the cropping period, except during the late fruiting stage. The pest number attai9ned a peak during the first week of November(12.92 S. dorsalis/shoot) and third week of May(16.48 S. dorsalis/shoot) in winter and summer season, respectively. Regarding the effect of weather parameters on S. dorsalis infestation, temperature (both maximum and minimum) was found to have positive effect. Relative humidity, rainfall and wind speed were found to have negative effect. The per cent damage due to attack of S. dorsalis on Bangalore Blue grapes was 5.67 and 33.18 during winter and summer, respectively. The efficacy of synthetic, contact and botanical insecticides viz., acephate 75% SP @ 0.075% verticel 100 SP 0.2% endosulfan 35 EC @ 0.07%. chlorphriphos 20EC @ 0.05% carbaryl 50% WDP, cartap hydrochloride 5% SP, fipronil 5% SC, fish oil rosin soap, azadirachtin 0.03 EC, endosulafan + azadirachtin and soil raking were evaluated against S. dorsalis on grapes in the form of two folia applications at 10 days interval. Of these endosulfan followed by cartap hydrochloride and carbaryl proved effective in the control of S. dorsalis during both the seasons. Whereas, fipronil, endosulfan+ azadirachtin and acephate had moderate effect, verticel and soil raking were less effective in controlling S. dorsalis.