Acaricidal activity and sublethal effects of an oxymatrine-based biopesticide on two-spotted spider mite (Acari: Tetranychidae).

Abstract

Lethal and sublethal effects of the biopesticide Kingbo (oxymatrine 0.2%+psoralen 0.4%) on the two-spotted spider mite (Tetranychus urticae Koch) were investigated in laboratory bioassays. The biopesticide was applied to bean leaf discs or primary leaves by using a Potter spray tower. Acute toxicity tests showed no significant ovicidal action: toxic effect (LC50=55.49μl/l) was the result of a residual activity against larvae that hatched from the treated eggs. Preovipositional females and female teleiochrysales showed similar susceptibility (LC50=52.68 and 59.03μl/l, respectively), whereas larvae, protonymphs and female deutonymphs were the most susceptible stages (LC50=6.88, 13.03, and 8.80μl/l, respectively). In a choice test, females preferred the untreated halves of leaves over the halves treated with 2,000, 1,000, and 500μl/l in the first 24h, and their oviposition in those treatments was significantly greater on the untreated halves after 24 and 48h, as well as the summed oviposition over 72h. Viability and reproduction of survivors, as well as population growth, were strongly affected after the treatments of preovipositional females and female teleiochrysales with 100, 50 and 25μl/l. On the other hand, sublethal effects on the females that survived treatment at the egg stage or reached adulthood from the eggs laid on the treated surface (treatments with 50 and 25μl/l) were significantly weaker. Acaricidal and sublethal effects of the biopesticide Kingbo were discussed as a starting point for further research aimed to improve management of T. urticae populations. Regulatory issues and safety concerns regarding further commercialization of this biopesticide are addressed as well.