Impacts of short-term ivermectin exposures on fruit flies

A short-term ivermectin (IVM) exposure method was newly established to demonstrate effects of sublethal concentrations of IVM on the wild-type fruit fly, Drosophila melanogaster. Using a conventional glass-vial contact approach, exposures to IVM (0.01 to 1000 ppm) for 12 h durations or less were selected to assess the downstream impacts of short-term IVM exposures (STIEs) on fruit flies. Under these conditions, all female flies produced significantly higher levels of reactive oxygen species and malondialdehydes in their ovaries. Additionally, females treated with IVM for 12 h under the STIE conditions exhibited significantly increased levels of DNA damages in their ovaries. Despite the negative impacts described above, the mean percent hatchability values obtained from the eggs oviposited by the IVM-exposed females were not statistically different when compared to the hatchability of the unexposed females. Two concentrations (1 and 10 ppm) of IVM were selected to determine transgenerational effects following short-term IVM exposures. F1, F2 and F8 flies exposed to IVM showed significantly delayed developments (2.5-3.2, 2.5-3.0, and 0.9-1.3 days delayed, respectively). F5, F11 and F17 females showed significantly delayed IVM-induced sluggish behaviors in the presence of lethal IVM (1 %, w/v). F18 females transgenerationally exposed to 1 ppm IVM exhibited significantly increased levels of Mrp1 (8.7-fold) and Cyp6g2 (5.9-fold) transcripts compared to unexposed flies. Comparatively, F18 females transgenerationally exposed to 10 ppm IVM showed significantly increased levels of Cyp9f2 (2.6-fold) transcripts. Current study clearly demonstrated the effects of sublethal IVM on parent and filial generations of fruit flies, providing an important step toward understanding development of IVM resistance under the STIE conditions.