Microwave Radiation and Heat Against Immature Stages of The Chinese Beetle Callosobruchus chinensis (Coleoptera: Chrysomellidae)
El-Sayed H. Tayeb , Adel-Fattah S. A. Saad, Hassan A. A. Mesbah and Mai A. Salama
The present study aimed to investigate the effect of certain physical methods (heat and microwave radiation) as non-pesticidal ways to control the Chinese beetle Callosobruchus chinensis (Coleoptera: Chrysomellidae). Exposure of 100 infested faba bean seeds implying different immature stages of C. chinensis, (egg, larvae or pupae) to a high level of temperature of 50° C for 15, 30, 45, 60, 75, 90, 105 and 120 min. showed that all stages were significantly sensitive at the highest exposure period of 120 min. Eggs were more tolerant to the tested level of high temperature of 50°C than larvae and/or pupae. The germination of the exposed broad faba been seeds to the same high temperature (50°C) for different periods was significantly affected and it was found that as the time of exposure increased the germination percentages decreased as compared with control.
Moreover, the exposure of the infested faba bean seeds with different immature stages of C. chinensis to low temperature levels (25, 10 and -14 ± 1° C) for 24h revealed that all these stages were highly sensitive to the lowest temperature of -14 ± 1° C. Decrease in temperature level resulted in a decreased the average of the emerged adults and consequently increased the reduction percentage of the produced progeny. The reduction of the progeny (emerged adults) post the treatment with the lowest tested temperature (-14° C) showed that the reduction percentage reached 100% for the treated eggs, larvae and pupae.
Results also illustrated that after 24 h post - treatments, the calculated percentages of seeds germination percentage was 46.67% due to their previous exposure to the lowest tested temperature (-14° C), which is less than the half level of full or complete germination of normal healthy faba bean seeds.
Exposure of the infested faba bean seeds with different developing stages of C. chinensis to microwave (900W) for different periods of 5, 10, 15, 20, 25 and 30seconds was found to be effective against all the immatures of insect-pest especially after a period of 30 seconds. These treatments also affected the germination of seeds; the percentages of germination were decreased as the exposure period to microwave radiation increased. The results suggested that both the tested physical methods of heat and microwave radiation could be regarded as suitable ecofriendly and non-insecticidal methods or tools for controlling the developing or the harboured and trapped immature stages of C. chinensis within the infested seeds.
Key words: Heat, Microwave, Chinese beetle Callosobruchus chinensis, immature stages, emerged adults, seed germination