Toxicidad de aceite de neem y un piretroide sobre adultos del gorgojo del maíz, en condiciones de laboratorio.

Abstract

The objective of the bioassay was to evaluate the fumigant toxic effect of neem oil (1.2ml/L) and cypermethrin (200mg/L) against Sitophilus zeamais (Motschulsky), determining mortality parameters, LC50 and TL50. The experimental design was completely randomized, with eleven treatments (concentrations) and five repetitions per treatment. Each repetition included 20 adults of S. zeamais, distributed in 30 mL glass bottles, each with two pairs of adults and two grams of food. Fumigant toxicity was evaluated by applying one drop of each concentration on a 0.5 x 0.5 cm sponge placed on the inner lid of the bottles. The concentrations tested were: For neem oil: 1.2 ml/L; 0.96ml/L; 0.72ml/L; 0.48ml/L; 0.24ml/L; and 0.00 ml/L (control). For cypermethrin: 200 mg/L; 160 mg/L; 120 mg/L; 80 mg/L; and 40 mg/L. Mortality observations were made every 12 hours. Analysis of variance (ANOVA) and Tukey tests were applied for statistical analysis. The adults used (F1) in the bioassay came from a mass rearing maintained in the Plant Health Laboratory (17±1°C and 65±10% RH). Concentrations of neem oil and cypermethrin resulted in mortalities of 98-100%, while the control showed a mortality of 1.0%. The LC50 for neem oil was 0.72 ml/L and for cypermethrin was 6.31 mg/L. The TL50s were similar for both products: 12 to 108 hours for neem oil and 12 to 44 hours for cypermethrin. The treatments had sublethal effects impacting the exposed adults on their offspring. Taking into account the exposure to neem oil and cypermethrin, it could have affected the viability of the eggs and larvae since the results of the bioassay showed a lower emergence of adults (F1) of S. zeamais.