Soft-Electron Beam and Gamma-Radiation Sensitivity and DNA Damage in Phosphine-Resistant and -Susceptible Strains of Rhyzopertha dominica

Abstract

The soft-electron beam (low-energy electrons) and gamma-radiation sensitivities of phosphine-resistant (PHR) and -susceptible (PHS) strains of adults lesser grain borer Rhyzopertha dominica (F.) were studied, with particular reference to DNA damage assessed using single-cell electrophoresis (comet assay). Results showed that mortality in adult R. dominica varied significantly between both PHR and PHS strains. Adults of the PHR strain were found to be more tolerant toward soft-electron and gamma radiation than adults of the PHS strain. Studies on the longevity of strains showed that mean survival time and dose rate were highly correlated with both strains and treatments. Results also showed that adults of the PHR strain lived longer than adults of PHS strain for both treatments. Radiation sensitivity indices, however, decreased as radiation dose increased in both strains. Analysis of DNA damage, after 40- and 160-Gy gamma radiation, was carried out using cells obtained from both strains. Gamma-irradiated adults of both strains showed typical DNA fragmentation, compared with cells from nonirradiated adults, which showed more intact DNA. Investigations using the comet assay showed that tail length, moment, olive-tail moment, percentage of tail DNA, and percentage of DNA damage were all greater in the PHS strain compared with the PHR strain and the control insects. Results also showed that DNA damage remained at a constant level for up to 24 h after irradiation. The results have been discussed in relation to the observed strain differences in radiation sensitivity and resistance to phosphine.

Attenuation of radiation toxicity by the phosphine resistance factor dihydrolipoamide dehydrogenase (DLD)

“…In these experiments, a phosphine resistant strain of R. dominica was more resistant to ionizing radiation than their phosphine-sensitive counterparts. While the resistance factor in these insects was not identified, the authors suggest that the phosphine resistant insects likely have the genetic ability to counter oxidative damage caused by phosphine, and can tolerate exposure to ionizing radiation since it has been reported to cause oxidative stress 21 . In support of their conclusions, antioxidants have been found to protect against phosphine exposure 28,29 .…”

“…However, exposure to the fumigants did not change sensitivity to ionizing radiation when it was administered after fumigation 19 . Phosphine was unique as gamma irradiation did not affect subsequent sensitivity to phosphine fumigation 20 , despite the fact that phosphine resistant individuals of R. dominica are more tolerant of ionizing radiation compared to their susceptible counterparts 21 .…”

Phosphine toxicity in Caenorhabditis elegans: synergy and cross-resistance with other pest control treatments, including gamma radiation

“…Crossresistance between gamma radiation and phosphine was observed in R. dominica. The phosphine resistant strain showed a significant increase in resistance to gamma irradiation compared with a phosphine susceptible strain (Hasan et al, 2006).…”

“…The authors discuss that the phosphine resistant insects have the genetic ability to counter oxidative damage caused by phosphine, and can tolerate exposure to ionizing radiation since it has been reported to cause oxidative stress (Hasan et al, 2006). They also conclude that antioxidants would provide protection against phosphine.…”

“…Phosphine was unique as gamma irradiation did not affect subsequent sensitivity to phosphine fumigation (Cogburn & Gillenwater, 1972). Phosphine resistant individuals of R. dominica were found to be more tolerant to ionizing radiation compared with their susceptible counterparts (Hasan et al, 2006).…”