Oxygen atmosphere potentiates radiation effects on Brevipalpus yothersi (Trombidiformes: Tenuipalpidae).

The objective of the study was to compare the effect of pure oxygen to that of ambient air on gamma irradiation of Brevipalpus yothersi (Baker) (Trombidiformes: Tenuipalpidae). Flasks containing the mites were irradiated in a Gammacell-220 irradiator with Cobalt-60 emitting gamma radiation at a rate of 381 Gy/h. Seventy mites per flask replicated 4 times were irradiated in either pure oxygen or air with 0 (control), 200, 230, 270, or 300 Gy as the intended doses. All eggs, deutonymphs and adults were counted each day and the parameters of egg production, egg hatch, development and mortality were recorded. Data were analyzed with ANOVA and means were separated with Tukey’s Honestly Significant Difference (HSD) test at 5% probability. Generally, irradiation of females with progressively larger doses—whether in oxygen or in air—resulted in progressively greater negative biological effects, and these effects were greater when females were irradiated in oxygen than in air. Non-irradiated gravid females exposed to pure oxygen deposited 79.3 ± 0.3 eggs per female compared to 73.0 ± 0.3 per female in ambient air. The numbers of eggs oviposited by females irradiated with the largest dose (300 Gy) were 29.1 ± 0.2 in air and 18.1 ± 0.3 in oxygen. In the ambient air + 270 Gy treatment egg hatch was 3.8 ± 0.1%, but in the oxygen + 270 Gy treatment it was 0%. When females were irradiated in air with 300 Gy, egg hatch was totally prevented. The number of F1 deutonymphs per P generation female irradiated with 270 Gy in ambient air was 4.0 ± 0.1, but the corresponding number that descended from females irradiated in pure oxygen was significantly reduced to zero. Percentage survival of females at 22 d post treatment was 13.0 ± 0.1 d when females were irradiated in oxygen with 270 Gy compared to 16 ± 0.2 d when irradiated in air with 300 Gy. Therefore, 300 Gy is recommended as an appropriate candidate for phytosanitary irradiation of B. yothersi in air, and 270 Gy is recommended as an appropriate candidate for phytosanitary irradiation of B. yothersi in oxygen. [ABSTRACT FROM AUTHOR]