The effect of thiamethoxam, a second generation neonicotinoid insecticide,in preventing transmission of tomato yellow leaf curl geminivirus (TYLCV) by the whitefly Bemisia tabaci (Gennadius)

The effect of thiamethoxam, a new neonicotinoid insecticide, in preventing transmission of tomato yellow leaf curl geminivirus (TYLCV) by the whitefly Bemisia tabaci has been studied by means of experimental transmissions to tomato seedlings. Source plants were foliar-treated while test plants were both foliar- and drench-treated at the six-leaf stage. Doses of 50 ppm a.i. for the foliar and of 7 mg a.i. per plant for the drench application were evaluated. Drench application to test plants provided a good level of prote ction From TYLCV infections in all tested conditions(from 1 to 22 days afte r treatment application); foliar application resulted in a prompt but short -lasting protection (<8 days). Foliar treatment of source plants made infec ted tomatoes totally ineffective as a virus source for at least 8 days. The proportion of viruliferous whiteflies surviving the acquisition on treated plants appeared similar to that of insects fed on untreated plants, sugges ting that thiamethoxam activity in preventing TYLCV transmission by B. tabu ci is simply due to its killing activity, and antifeeding or repellent acti ons can be excluded. Viruliferous whiteflies exposed to thiamethoxam-treate d plants stopped feeding before acquiring enough virus to subsequently inoc ulate plants. (C) 2000 Elsevier Science Ltd. All rights reserved.