RESUMEN
BACKGROUND: The corn leafhopper, Dalbulus maidis, is an important pest in Brazil. While chemical control has traditionally been the cornerstone for managing this pest, field control failures have been reported for some insecticides. To understand if these failures are due to resistance, we evaluated the susceptibility of 11 field-collected populations of D. maidis to major insecticides during the 2021-2022 crop seasons in Brazil using concentration-mortality bioassays. Additionally, we employed diagnostic concentration bioassays and foliar sprays at label-recommended rates in 8-10 populations collected during the 2022-2023 crop seasons. RESULTS: High susceptibility to methomyl, carbosulfan and acephate was observed on concentration-mortality bioassays across all populations tested with resistance ratio (RR) based on LC50 <10-fold, except for one population from Bahia State that exhibited reduced susceptibility to methomyl (RR = 17.5). On the other hand, all populations exhibited reduced susceptibility to bifenthrin, acetamiprid, and imidacloprid, with RR ranging from 90 to 2000-fold. This reduced susceptibility to neonicotinoid and pyrethroid insecticides was further confirmed at diagnostic concentrations based on LC99 of the susceptible strain, with survival rates >20% and in foliar sprays with mortality rates <80%. Most populations exposed to acephate and carbosulfan exhibited low survival rates at diagnostic concentrations (<5%) and high mortality rates in foliar sprays (>80%). CONCLUSIONS: The reduced susceptibility to pyrethroid and neonicotinoid insecticides likely explain the field failures in controlling D. maidis populations in Brazil. This study represents the first large-scale susceptibility monitoring of D. maidis to insecticides, and the results will contribute to decision-making regarding the management of this pest. © 2024 Society of Chemical Industry.
RESUMEN
The objectives of the present work were control the decay incidence and ripening of wounded fruits by the relative humidity management during the storage. Fruits were allocated in mini experimental chambers at the temperature of 1°C during 5 months. Was verified a significant interaction on ethylene production after 2 and 6 days of shelf life at 20°C. On the evaluation carried out after 6 days, wounded fruits stored under LRH showed lower ethylene production. There was higher mass loss in wounded fruits stored in HRH. Wounded fruits showed high decay incidence. The LRH is not an efficient method to control decay incidence in wounded fruits, but maintain higher flesh firmness, lower ethylene production and respiration rate.
Objetivou-se neste trabalho controlar a ocorrência de podridões e o amadurecimento de frutos com ferimentos pelo manejo da umidade relativa (UR) durante o armazenamento. Os frutos foram acondicionados em minicâmaras experimentais na temperatura de 1°C durante um período de cinco meses. Observou-se uma interação significativa para produção de etileno aos dois e seis dias de exposição a 20°C. Na análise aos seis dias, frutos com ferimento em baixa umidade relativa (BUR) apresentaram menor produção de etileno. Houve maior perda de massa em frutos com ferimento em alta UR. Frutos com ferimento apresentaram elevados índices de podridão. O uso de BUR não é eficiente no controle de podridões em frutos com ferimentos, porém ela mantém maior firmeza de polpa, menor produção de etileno e taxa respiratória.