~ 38 ~ Journal of Entomology and Zoology Studies 2019; 7(2): 38-42 E-ISSN: 2320-7078 P-ISSN: 2349-6800 JEZS 2019; 7(2): 38-42 © 2019 JEZS Received: 21-01-2019 Accepted: 23-02-2019 SH Shweta M. Sc. (Hort.) Entomology University of Horticultural Sciences, Bagalkot, Karnataka, India N Gangadhar Assistant Professor and Head, Department of Entomology University of Horticultural Sciences, Bagalkot, Karnataka, India JB Gopali Professor, Department of Entomology, University of Horticultural Sciences, Bagalkot, Karnataka, India MP Basavarajappa Assistant Professor, Department of Plant Pathology University of Horticultural Sciences, Bagalkot, Karnataka, India HP Hadimani Assistant Professor, Department of Vegetable Science University of Horticultural Sciences, Bagalkot, Karnataka, India Correspondence SH Shweta M. Sc. (Hort.) Entomology University of Horticultural Sciences, Bagalkot, Karnataka, India Bio-efficacy of synthetic insecticides against onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae) SH Shweta, N Gangadhar, JB Gopali, MP Basavarajappa and HP Hadimani Abstract The experiment was conducted under field condition at Haveli Farm, University of Horticultural sciences, Bagalkot to evaluate the efficacy of synthetic insecticides against onion thrips during kharif season (2017 - 18). The experiment plot area was replicated thrice and eight treatments with randomised block design. The results revealed that thiamethoxam 25 WG @ 25 g a.i./ha recorded significantly lowest population of thrips after first, second and third spray during the experimental period by recording 4.90 thrips per plant which was at par with imidacloprid 17.8 SL @ 22.25 g a.i./ha with 5.19 thrips per plant indicating the superiority of both the treatments against onion thrips. The next best treatments were, cyazypyr10.26 OD @ 76.95 g a.i./ha, diafenthiuron 50 WP @ 250 g a.i./ha and tolfenpyrad 15 EC @ 150 g a.i./ha with 6.89, 7.29 and 7.56 thrips per plant, respectively. Whereas, lamda cyhalothrin 5 EC @ 12.5 g a.i./ha and chlorfenapyr 10 SC @ 12.5 g a.i./ ha found to be least effective in reducing thrips population with 8.67 and 8.46 thrips/plant. The data on bulb yield indicated that highest bulb yield was registered in thiamethoxam 25 WG @ 25 g a.i./ha and imidacloprid 17.8 SL @ 22.25 g a.i./ha treated plots with 25.39 and 24.67 t per hectare, respectively. Whereas, minimum bulb yield was noticed with lambda cyhalothrin 5 EC @ 12.50 g a.i./ha treated plots (17.94 t/ha). Keywords: Onion thrips, synthetic insecticides, bulb yield 1. Introduction Onion (Allium cepa L.) belongs to the family Amaryllidaceae (Alliaceae) is one of the most important commercial vegetable and condiment crop grown in India for more than 5000 years. It is consumed throughout the socioeconomic spectrum [1] . India is the second largest onion producing country in the world, next only to china. It contributes 11.9 per cent of total onion production in the world with a production of 215.63 lakh tones and 21.2 MT/ha productivity with an area of 1.27 million ha. Major onion producing states are Maharashtra, Karnataka, Madhya Pradesh, Andhra Pradesh, Rajasthan, Tamil Nadu and Haryana. In Karnataka, it occupies an area of 0.19 million ha with production of 27.67 lakh tones and productivity of 14.16 MT/ha. Dharwad, Chitradurga, Bijapur, Bellary and Gulbarga are major districts of onion cultivation in Karnataka [2] . Onion crop is subjected to attack by various insect pests right from seedling stage to harvest, that can reduce yield and quality. The important ones are onion thrips, Thrips tabaci Lindeman, head borer, Helicoverpa armigera (Hubner), onion maggot, Delia antiqua (Meigen), tobacco caterpillar, Spodoptera litura (Fabricius) and cut worm Agrotis ipsilon (Hufn.) [3] . Among the insect pests, onion thrips, Thrips tabaci is one of the major limiting factor in reducing the productivity and reported to cause significant economic losses up to 30-50 per cent [4] . Onion thrips is a cosmopolitan pest which is recorded on more than 300 species of host plants mainly cabbage, cotton, carnation, garlic, onion and cereals especially wheat [5] . Both nymphs and adults are the damaging stages which feed by rasping the leaves and other tissues of plants and suck the sap, as a result, it causes silver patches and streaks on leaves. Besides direct damage to foliage, it can indirectly aggravate purple blotch [6] . It is also a vector of “Iris Yellow Spot Virus” which is a tospovirus causing adverse effects on bulb and seed yield of onion crop in India. More often use of insecticides is one of the most common and popular methods of thrips control on onion crop. These chemicals need to be used wisely in the control or management of any key pest like onion thrips with due consideration of cost economics and