Microwave radiation and conductive heating were used to completely kill adult Tribolium castaneum
(Coleoptera: Tenebrionidae) in wheat flour to protect the flour during storage without significantly effecting
its quality. The microstructure of T. castaneum was analyzed to reveal the mechanisms leading to
death under microwave and heat treatments. Microwave radiation and conductive heating had different
effects on the microstructure of the cuticle of adult T. castaneum and on the ultrastructure of the cells of
the epidermis, fat body, and midgut. Both treatments caused a large cavity to appear in the nucleus and
the disappearance of mitochondria and the Golgi apparatus. After microwave treatment, there was little
change in the surface microstructure but the epidermis was of uneven thickness and the four outer layers
of the cuticle were thinner. Nuclear size was essentially unchanged, but fat body cells were fewer and
coalesced together. In contrast, conductive heating led to a disordered arrangement of cells on the surface
of T. castaneum and indistinct boundaries between layers of the cuticle. The nuclei were enlarged and the
fat body cells noticeably fewer and indistinct with a scattered distribution. Thus, microwave treatment
produced less severe effects on the surface microstructure and cellular ultrastructure of T. castaneum
than did conductive heating. It is concluded that these cellular and surface changes were responsible for
the death of T. castaneum.