Microwave radiation for the management of red flour beetle, Tribolium castaneum (Herbst) (Coleoptera:Tenebrionidae)

Abstract

Red flour beetle, Tribolium castaneum, is a cosmopolitan stored grain pest imparting severe economic loss in cereal-based products, especially wheat flour. Microwave irradiation, an eco-friendly physical management strategy without any residual effect on food and less resistance development, can be an alternative to chemical control measures. Hence, the study entitled “Microwave radiation for the management of red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)” was conducted to assess the effectiveness of household microwave system for the management of red flour beetle, T. castaneum and to study the effect of microwave radiation on nutritional factors of wheat flour. The experiment was carried out from January 2021 to October 2021 at Pesticide Residue Testing Laboratory, Department of Agricultural Entomology, and at the Agri-Business Incubator, College of Agriculture, Vellanikkara, Kerala Agricultural University, Thrissur. All the developmental stages of T. castaneum were irradiated at five different microwave powers (136, 264, 440, 616 and 800 W) by varying the flour bed thickness of wheat flour at five levels (1, 2, 3, 4 and 5 cm) and exposure time at six levels (10, 20, 30, 40, 50 and 60 s) along with unirradiated control. Eggs (two days old), grubs (20±2 day old), pupae and adults (17±2 day old) of T. castaneum were irradiated in a household microwave to assess the susceptibility of various life stages. Larvae were most vulnerable to irradiation. Susceptibility of eggs and adults but were comparable to each other, while the pupal stage exhibited relatively higher tolerance to microwave treatment. Microwave power was directly proportional to the mortality of all life stages of T. castaneum. The mortality of egg, pupa and adult was highest at 800 W power level, whereas pupal mortality was comparable and higher at 616 and 800 W. The death rate of all the developmental stages was highest at the lowest flour bed thickness of one cm. Similar to the effect of microwave power, exposure period and mortality was directly proportional to each other. At the longest exposure time (60 s), egg, grub and adult mortality was high and pupal mortality at 50, and 60 s was comparable. The analysis on the interaction of power and thickness revealed that mortality of all stages of T. castaneum increased with an increase in power level and decrease in flour bed thickness. In power-time interaction, higher irradiation dose and longer exposure period resulted in higher mortality of T. castaneum. The interaction effect of thickness and time showed that mortality was higher at lower flour bed thickness and longer exposure time. The analysis on the interaction of power, thickness and time recorded higher mortality at higher dose, lower thickness and longer exposure period of microwave radiation. The best two treatment combinations that recorded complete mortality of all life stages of T. castaneum was 800 W irradiation dose exposed for 50 s at higher flour bed thicknesses of four and five cm. The comparison of nutritional parameters of the two treatments with control indicated a decrease in moisture content. The gluten content and colour were unaffected by irradiation. There was an increase in vitamin B1, B2 and B6 and a slight decrease in vitamin B3 content in treated samples compared with control. Microwave irradiation of wheat flour at 800 W for 50 s at a flour thickness of five cm is the best treatment combination for the management of red flour beetle because of the efficacy, ease of application, lack of residual effect without affecting the nutritional quality.