The impact of microwaves irradiation and temperature manipulation for control of stored-products insects
The impact of microwaves irradiation and temperature manipulation against adults of saw-toothed grain beetle, Oryzaephlius surinamensis (L.) and cigarette beetle, Lasioderma serricorne (F.), over various exposure times and cold storage period was evaluated. The insects were exposed to 2450 MHZ at five different power levels of 0, 100, 200, 300 and 400 W for five exposure times of 0, 3, 6, 9 and 12 min. A complete control was achieved for tested insects at 400 W power levels for exposure time of 12 min and 72 h cold storage period. At a given time, a direct positive relationship between the mortality rates and microwaves irradiation power levels was obtained. For O. surinamensis at 100, 200, 300 and 400 W power levels and 24 h cold storage for 3 min exposure period, the mortality rates were 40, 50, 55 and 72%, respectively. Similar trend was also observed for L. serricorne. Substantiate variation in the susceptibility of tested insects to microwaves energy and cold storage period was apparent in the overlapping confidence interval of the LD50 values. In the analysis of variance (ANOVA) the R-squared value revealed that 90.8% of variability in the susceptibility of O. surinamensis could be explained by the microwaves power, cold storage period and exposure duration. This criterion was 93.2% for cigarette beetle. As expected, all of the first and second order interactions were significant. Moreover, there was sufficient evidence that the most important factor was the exposure period, followed by power level and cold storage time. The exposure period showed a higher omega-squared (ω2) value, which implies substantial contribution to explaining insect mortality variations. Combinations of microwaves radiation and cold storage were found highly compatible and synergistic. This was more significant for the insects which were exposed to the highest level of the microwaves irradiation and cold storage period. Synergistic interaction indicates that, microwave irradiation can be used with cold storage for management of the insects in question. This treatment could provide an effective and friendly environmental treatment technique in integrated pest management (IPM) program.
Key words: Cold storage, microwaves, saw-toothed grain beetle, cigarette beetle.