Ozone as an alternative fumigant for controlling Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae) in cowpea beans

Abstract

This study aimed to characterize the reaction kinetics of ozone gas in cowpea beans, to determine its insecticidal activity against Callosobruchus maculatus adult insects, and to assess grain quality after ozonation. Samples of 3.0 kg of cowpea beans were exposed to ozone gas at inlet concentrations of 500, 1,500, 2,500, and 3500 μg L−1, at a specific flow rate of 0.5 L min−1 kg−1 of grains. Moisture content, cooking time, germination percentage, and electric conductivity of the grains were analyzed. Grain quality was evaluated after exposure to the gas for periods corresponding to the lethal time to 95% of the insects (LT95), at each ozone concentration. The cowpea samples exposed to ozone at the inlet concentrations of 500, 1,500, 2,500, and 3500 μg L−1 got saturated with the gas after 45.18, 20.11, 16.86, and 14.70 min, respectively. The first-order kinetic model provided the best fit to the ozone decay data in cowpea beans. The average half-life of ozone in the grains was 6.88 ± 0.48 min. The estimated lethal times at the inlet ozone concentrations of 500, 1,500, 2,500, and 3500 μg L−1 were 777.27, 133.27, 84.29, and 52.33 min (LT50), and 1698.00, 331.20, 157.07, and 84.40 min (LT95), respectively. Callosobruchus maculatus adult progeny declined as the exposure time increased, at all inlet ozone concentrations. Cowpea bean quality did not change after ozone exposure, except for the electric conductivity, which differed between the grains exposed to ozone and those to atmospheric air. The results of this study indicate that ozone gas controls C. maculatus effectively and, in general, does not change the quality of cowpea beans at the inlet concentrations and exposure times appraised.