Toxicity of Organosilicone Adjuvants and Selected Pesticides to the Asian Citrus Psyllid (Hemiptera: Psyllidae) and its Parasitoid Tamarixia radiata (Hymenoptera: Eulophidae)

Arturo Cocco, Marjorie A. Hoy


The acute toxicity of the adjuvants Silwet L-77 and Kinetic, alone and in combination with petroleum oil and copper hydroxide, to the Asian citrus psyllid Diaphorina citri Kuwayama was evaluated in screenhouse bioassays. In addition, the acute and residual toxicity of Silwet L-77 and Kinetic, alone and in combination with petroleum oil, copper hydroxide, imidacloprid, and abamectin, to the parasitoid Tamarixia radiata (Waterston) were evaluated under laboratory conditions. In screenhouse trials, Silwet L-77 (0.05%) was more insecticidal than Kinetic (0.05%) and increased the toxicity of both petroleum oil and copper hydroxide to D. citri. Petroleum oil at reduced rates (0.5 and 1%) in combination with Silwet L-77 or Kinetic was less effective in reducing D. citri populations than petroleum oil at 2% in combination with these adjuvants. Petroleum oil at 2% plus Silwet L-77 was the most toxic combination to D. citri eggs, young (first- and second- instars) and mature nymphs (third- to fifth-instars), and adults (81, 83, 74, and 55% mortality, respectively). Copper hydroxide was only toxic to young nymphs when combined with Silwet L-77 (64.9% mortality). Under laboratory conditions, survival of T. radiata was reduced by the residual effects of imidacloprid (>95% mortality) and by the acute toxicity of abamectin (>91% mortality). Silwet L-77 and Kinetic alone, and petroleum oil and copper hydroxide alone or in combination with these adjuvants, had low residual and acute toxicity to the parasitoid and appear to be compatible with the biological control of D. citri by T. radiata. The results of this study suggest that Silwet L-77 may be used in a citrus IPM program in combination with petroleum oil or copper hydroxide to increase psyllid control while spraying to suppress other insect pests or plant diseases. Field trials should be conducted to evaluate the effectiveness of these products against D. citri and their impact on T. radiata populations.

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