Toxicidade e compatibilidade físico-química de misturas de inseticidas botânicos a base de limonoides e reguladores de crescimento de origem sintética a Spodoptera frugiperda (Lepidoptera: Noctuidae)

Abstract

The Brazil is considered one of the largest corn (Zea mays) producers in the world. One of the main challenges for each crop is related to the management of Spodoptera frugiperda (J. E. Smith 1797). This fact has increased in recent years due to the rapid evolution of pest resistance to different chemical insecticides and Bt plants. Faced with this, new alternatives or products are increasingly being studied and evaluated to try to enable the management of the species in the field, emphasizing sustainable alternatives with less environmental impact. The present study aimed to characterize the azadirachtin content of different commercial formulations of neem-based insecticides (Azamax® , Agroneem® , Azact® and Fitoneem® ) and evaluate the physical and chemical compatibility and toxicity with growth regulating insecticides (IRCs) (Certero® , Intrepid® , Mach® and Mimic® ) when used in mixtures on S. frugiperda larvae in laboratory and field. Through bioassays of ingestion in artificial diet, all neem formulations evaluated caused significant lethal toxicity on S. frugiperda larvae. Azamax® and Agroneem® were the products that provided the highest mortality (larval mortality > 70%) after 168 hours of exposure. However, such mortality levels were lower than that observed (98.9%) in the positive control (Insecticide Premio® - chlorantraniliprole 200 g.L-1 ). Furthermore, all commercial neem-based formulations provided high inhibition of larval development. According to the chemical profile, it was verified that Azamax® was the product that presented the highest azadirachtin content (3.94 g kg-1 ) in relation to the other formulations. When evaluating the biological parameters of S. frugiperda, a significant sublethal effect was observed on the duration and viability of the larval stage and egg-adult period, larval weight at 7 days, weight of pupae until 24-hour, duration, oviposition period, and total fecundity when using lethal concentrations (LC25 or LC50) of IRC insecticides and limonoid-based incorporated into the diet. This fact that directly affected the parameters of the fertility life table. In bioassays of mixtures of insecticides, all combinations of the four IRCs and the four formulations based on neem derivatives showed a significant reduction in syrup pH and a significant increase in electrical conductivity. However, all tested combinations showed similar grout stability behavior when they were prepared with water only, which demonstrates their physical compatibility. Furthermore, in laboratory and field bioassays, mixtures of IRCs with formulations based on limonoids showed a synergistic effect in the management of S. frugiperda. In view of the results achieved, the use of IRCs and formulations based on neem derivatives, alone or in 11 combination, presented lethal and sublethal effects on S. frugiperda, constituting promising alternatives for the pest, combining control efficacy and selectivity, important aspects for integrated management programs.