Toxicity of non-ionic surfactants against Bemisia tabaci biotype B by direct spray contact

Nonionic surfactants are important additives in numerous chemical and biological pesticides. These compounds reduce water tension and enhance spray coverage on hydrophobic surfaces. In addition, some exhibit direct toxicity against soft-body insects and mites. This study aimed to investigate the toxicity of four commercial surfactants (Break-thru^®, Silwet L77^®, Soub’oil^® and Agral^®) on early (2^nd instar) and late (3^rd instar) nymphs of Bemisia tabaci biotype B under laboratory conditions. Dry bean leaves (cv. Pérola) infested with nymphs were sprayed (2.15 µL/cm²) with aqueous solutions of surfactants at 100, 200, 400, 600 and 800 ppm. The spreading performance on a paraffinic surface was also assessed over the range 100–1000 ppm. Tween 80^® was used as a standard. Surfactants (Break-thru, Silwet L77 and Solub’oil) showed direct insecticidal activity to early nymphs (LC₅₀ 120-150 ppm), whereas Agral was less toxic (LC₅₀ 1225 ppm). Late nymphs were less susceptible to trisiloxane compounds (Break-thru and Silwet L77) with LC₅₀ values of 220–289 ppm. In addition, trisiloxane surfactants were also superior spreading agents in laboratory tests, which might be related to their enhanced toxicity towards whitefly nymphs. It is expected that inclusion of trisiloxane surfactants in pesticide sprays could be beneficial for the management of whiteflies by improving both coverage and also providing direct mortality to younger life stages.