Effect of heat treatment on developmental stages of Callosobruchus maculatus (Coleoptera: Bruchidae) in stored adzuki bean Vigna angularis

Abstract

Effect of heating on Callosobruchus maculatus (Fabricius) in Vigna angularis (Willd.), Ohwi & Ohashi, seed was assessed using an 118° obtuse base angle solar box heater. The box heater was constructed with 1.2 mm thick sheet metal, glued inside with aluminium foil and insulated on the outside by fixing 1 cm thick polystyrene and glazed with 0.15 mm thick clear plastic sheet. Electric energy from a solar simulator panel adjusted to simulate heat trapped from natural solar energy was used. Exposure of the various developmental stages of C. maculatus infesting adzuki bean seed to heat for 45 min and more raised the temperature between and within the seeds well in excess of the lethal level (>60 °C) and resulted in complete control. Heating at 60°C of up to 3 cm adzuki bean seed (seven to eight seed layers) took about 1 h and resulted in complete control of the pest. This would enable this heater to treat large amounts of seed at a time compared with solar heaters demonstrated so far in which only a single layer of seed can be treated. Therefore, solar heating of infested adzuki bean seeds using the aforementioned box heater around noon, for 1 h, gives effective control of C. maculatus . Results of the effect of heat treatment on seed viability and moisture content showed that adzuki bean seed germination is affected by heating; hence seed meant for planting should not be heat treated to control storage insect pests. Heat treatment also did not affect seed moisture content.