Activity of Flonicamid and Two Neonicotinoid Insecticides against Bemisia tabaci (Gennadius) and Its Associated Predators on Cotton Plants

The sweet potato whitefly, Bemisia tabaci (Genn.), is a world-wide pest causing severe damages to numerous economic crops and has acquired resistance to most of conventional insecticides, particularly organophosphates and pyrethroids. Hence, Flonicamid, thiamethoxam and imidacloprid were evaluated for their efficacy against different developmental stages of B. tabaci on cotton plants under laboratory and field conditions at Sakha Agricultural Research Station, Egypt, during the cotton growing seasons of 2016 and 2017. Their side effects on the predacious stages of the associated predators i.e., the larvae of Chrysoperla carnea, both adults and larvae of Coccinella spp. and Scymnus spp., and true spiders were studied in the field as well. Results of the laboratory trials indicated that flonicamid provided no insecticidal activity on B. tabaci eggs, while thiamethoxam was significantly the most effective with LC₅₀ value of 37.38 mg a.i.L^-1. Thiamethoxam possessed the highest toxic effect against the 2^nd instar nymphs followed by imidacloprid and flonicamid recording LC₅₀ values of 30.37, 136.41, and 226.54 mg a.i.L^-1, respectively. Under the field conditions, the activity of thiamethoxam did not differ significantly from that of imidacloprid recording from 83.19 ــ 93.24% and from 77.02 ــ 82.48% control of adults and immature stages of B. tabaci, respectively. Flonicamid demonstrated sufficient control, where it resulted in 75.67 to 80.64% and 64.97 to 69.58% reduction in the adults and immature stages, respectively. All the tested insecticides were more effective against adults than immature whitefly. Flonicamid was significantly the most harmless to the associated predators causing 21.01 to 23.75% reduction. Thiamethoxam and imidacloprid resulted in 35.24 to 49.96% reduction in the associated predator's population. These results suggest that flonicamid, thiamethoxam and imidacloprid could be successfully incorporated in IPM programs to control B. tabaci under the field conditions.