Non-thermal plasma as emerging technology for Tribolium castaneum management in stored grains and flours.

Abstract

The red flour beetle, Tribolium castaneum (Herbst), is a major secondary pest on wheat stored in metal bins, silo-bags and is also frequently found in wheat products such as flour. Non-thermal plasmas (NTPs) are (quasi-neutral) partially ionized gases that may be produced by a variety of electrical discharges. Among the variety of NTP sources, we propose the use of an atmospheric pressure dielectric barrier discharges (DBD) as an emerging technology in the post-harvest integrated pest management. To this aim, a series of experiments were performed in order to test the lethality of such plasmas on three life stages of T. castaneum by measuring insect mortality, but also different physiological and biochemical parameters affecting insect fitness. The different NTP treatments were performed by increasing time of exposure to either O2 or N2 used as carrier gases. After 24 h, high levels of mortality (from 30 to 100%) were reached for each applied treatment, in both, larval and adult populations. In general, better results were always obtained under nitrogen environment. Mortality seems to be related to a significant water content loss and redox imbalance. The scanning of the cuticle prothorax segment using the atomic force microscopy (AFM) technique revealed that oxygen and nitrogen discharges impacted the surface body in a different way. As a consequence of the cuticle damage, the quinone-containing secretions of the prothoracic and abdominal glands were also affected. Since has been reported that egg is the most resistant stage of the T. castaneum life cycle, we carried out experiments on egg-containing flours to test the ovicidal activity of NTP, and the flours were evaluated at three and twelve weeks after treatments. We clearly identified one ovicidal nitrogen treatment, while the remaining NTPs just partially killed the eggs and delayed the development of life cycle. In conclusion, we identified an inexpensive physical treatment, which controls the entire life cycle of a major grain pest, avoiding chemical residues.