Electron beam irradiation induces DNA endoreplication in holometabolous juvenile insects: a rapid flow cytometry-based diagnosis

Ionizing radiation including electron beam (eBeam) technology has been used as a quarantine measure around the world for transboundary shipment of agricultural products. Since the treatment goal of this technology is not to instantly kill insects but to cause them to be sterile, an apparent challenge is how to ensure that the agricultural commodities have been exposed to ionizing radiation if live insects are found. Because irradiation affects DNA synthesis and cell division, we investigated the feasibility of using flow cytometry detection of eBeam irradiation-induced ploidy change as a diagnostic tool. All eBeam-treated holometabolous insects tested including cowpea bruchid (Callosobruchus maculatus), corn earworm (Helicoverpa zea) and fruit fly (Drosophila melanogaster) displayed significantly higher proportions of polyploid cells than their respective unirradiated controls. However, such increased DNA ploidy was mostly absent in irradiated hemimetabolous sand field cricket (Gryllus firmus), green peach aphid (Myzus persicae) and potato/tomato psyllid (Bactericera cockerelli). Further studies with representative holometabolous insects revealed that the eBeam-triggered DNA endoreplicative response was strong in larvae, but became weaker as insects continued to develop into pupae and was even diminished in adults. Therefore, the flow cytometry-based method has the potential to be developed into a diagnostic tool to determine whether juvenile insects found on agricultural shipments, particularly those that undergo complete metamorphosis, have received irradiation as a quarantine treatment. This simple and rapid detection method could potentially resolve the dilemma that occurs in border control and domestic movement of plant material and products from areas under quarantine.