Toxicidade de novos Aminoaril-Fosforamídicos sobre Spodoptera frugiperda (Lepidoptera: Noctuidae) e seu potencial inimigo natural, Polybia occidentalis (Hymenoptera: Vespidae)

Abstract

Phosphoramidates are a class of compounds that feature at least one -NR1R2 group (R1 and R2 = Alkyl, Aryl) directly attached to the phosphorus atom in their structures. Compounds from this class are mentioned as potential insecticidal agents. In this work, we generally discuss the synthesis of three new aminoaryl-phosphoramidic compounds and, under laboratory conditions, we evaluated the lethal toxicity of these compounds when applied topically to the pest insect Spodoptera frugiperda (Smith, 1797) (Lepidoptera: Noctuidae), commonly known as the "fall armyworm," as well as their lethal effect on an organism considered potentially beneficial to agriculture, including against this pest, the predatory wasp Polybia (Myrapetra) occidentalis (Olivier, 1792) (Hymenoptera: Vespidae), commonly known in Brazil as the "marimbondo-farinha-seca." S. frugiperda larvae used in the experiment were reared on an artificial diet, and adult wasps were collected from field colonies and maintained in the laboratory. The acute lethal effect (considered in our study up to 72 hours post topical application) of the phosphoramidate compounds on S. frugiperda larvae was significantly lower compared to the control treatment (a commercial product). However, this acute lethal effect was significantly higher on the beneficial insect (wasp). After the topical application of the phosphoramidate compounds, ad libitum food was offered to the insects, and under this condition, possible delayed neuropathy was assessed, inferred by insect mortality over time. For S. frugiperda larvae (considered up to 360 hours post topical application of the compounds), the LD50% for aminoaryl-phosphoramidic compounds 1, 2, and 3 were respectively 99.34, 28.10, and 80.28 μg/mg of larva. For P. occidentalis workers, the LD50% for phosphoramidic compounds 1, 2, and 3 were respectively 68.71, 60.98, and 74.06 μg/mg of wasp. Considering the rule that neurotoxic insecticides should promote rapid mortality of the pest, the phosphoramidates investigated in our study, compared to a commercial product with a similar mode of action, were not found to be suitable for future use in effective crop control. Moreover, they appear to be more toxic to the beneficial insect (wasp) compared to the pest.