60Co-γ Radiation Alters Developmental Stages of Zeugodacus cucurbitae (Diptera: Tephritidae) Through Apoptosis Pathways Gene Expression

Abstract

Radiation is considered as a promising insect pest control strategy for minimizing postharvest yield losses. Among various techniques, irradiation is a method of choice as it induces lethal biochemical or molecular changes that cause a downstream cascade of abrupt physiological abnormalities at the cellular level. In this study, we evaluated the effect of 60Co-γ radiation on various developmental stages of Zeugodacus cucurbitae Coquillett and subsequent carry-over effects on the progeny. For this purpose, we treated eggs with 30- and 50-Gy radiation doses of 60Co-γ. We found that radiation significantly affected cellular antioxidants, insect morphology, and gene expression profiles. Our results indicate that in response to various doses of irradiation reactive oxygen species, catalase, peroxidase, and superoxide dismutase activities were increased along with a significant increase in the malondialdehyde (MDA) content. We observed higher mortality rates during the pupal stage of the insects that hatched from irradiated eggs (50 Gy). Furthermore, the life span of the adults was reduced in response to 50 Gy radiation. The negative effects carried over to the next generation were marked by significantly lower fecundity in the F1 generation of the irradiation groups as compared to control. The radiation induced morphological abnormalities at the pupal, as well as the adult, stages. Furthermore, variations in the gene expression following irradiation are discussed. Taken together, our results signify the utility of 60Co-γ radiation for fruit fly postharvest management.

Keywords: Melon Fly; Tephritidae; antioxidant enzymes; apoptosis; gene expression; reactive oxygen species.

Fig. 1.

Effects of ⁶⁰Co-γ irradiation on (a) CAT, (b) SOD, (c) POD, (d) ROS activity, and (e) MDA content of Z. cucurbitae larval stages and pupae at different radiation doses. The values are presented as the mean ± SD. Treatments were compared using two-way ANOVA (Tukey’s test, P < 0.05) with a 0.05 level of significance (95% confidence interval). The symbol (**) represents P < 0.05, (ns) non-significance.

Fig. 2.

Effects of ⁶⁰Co-γ irradiation on (a) hatching rate (%) of eggs; (b) mortality rate (%) at the larval, pupal and adult stages; (c) development time duration of the larval, pupal and adult stages; and (d) F1 fecundity. The values are presented as the mean ± SD. Treatments were compared using two-way ANOVA (Tukey’s test, P < 0.05) with a 0.05 level of significance (95% confidence interval). The symbol (**) represents P < 0.05, (ns) non-significance.

Fig. 3.

Malformation caused by ⁶⁰Co-γ radiation in pupal-adult stage of Zeugodacus cucurbitae after eggs were exposed to 30 and 50 Gy of ⁶⁰Co-γ gamma radiation. The arrow shows that flies were failed to shed their old cuticle and were attached with their abdomen.

Fig. 4.

Ultrastructural observations of midgut cells of Z. cucurbitae larvae. (A) Observation of the structure of the mitochondria. Magnification: 8000×; scale: 2 μm. (B) Observation of the structure of the microvilli (MV). Magnification: 5000×; scale: 4 μm.

Fig. 5.

Expression levels of seven oxidative stress related genes: Cu/ZnSOD (SOD1), Cu/ZnSOD (SOD2), MnSOD (SOD3), catalase (CAT), peroxidase (Pxd), peroxidase-4 (Pxt), and caspase-3 in the pupal stage of Z. cucurbitae after ⁶⁰Co-γ radiation. The values are presented as the mean ± SD. Gene expression was compared using two-way ANOVA (Tukey’s test, P < 0.05) with a 0.05 level of significance (95% confidence interval). The symbol (**) represents P < 0.05, (ns) non-significance.