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 protection From TYLCV infections in all tested conditions(from 1 to 22 days after treatment application); foliar application resulted in a prompt but short-lasting protection (<8 days). Foliar treatment of source plants made infected 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, suggesting that thiamethoxam activity in preventing TYLCV transmission by B. tabuci is simply due to its killing activity, and antifeeding or repellent actions can be excluded. Viruliferous whiteflies exposed to thiamethoxam-treated plants stopped feeding before acquiring enough virus to subsequently inoculate plants. (C) 2000 Elsevier Science Ltd. All rights reserved.