Mating combinations of control and ivermectin-fed dung flies Neomyia cornicina (Diptera: Muscidae): effects on mating behaviour, oviposition and ovarian development

Abstract

AbstractThe dung fly Neomyia cornicina (Fabricius) fed on either control dung or dung containing 0.15 μg g−1 ivermectin were mated in the following combinations: (a) control male × control female, (b) control male × ivermectin-fed female, (c) ivermectin-fed male × invermectin-fed female and (d) ivermectin-fed male × control female. Frequency and duration of mating attempts by males during 10 min mating trials were significantly higher when males were placed with control females, irrespective of male treatment. There was no significant difference between groups in the frequency and duration of all other behaviours observed. There was a significant effect of mating combination on the percentage of females that laid eggs, with most laying in groups where females were controls (groups a and d). There was also significant effect of mating combination on the time to first oviposition, with control females mated with control males (group a) laying earliest. Egg batch size was unaffected by treatment group. At the end of the experiment, all females were dissected and the number, size and yolk content of the terminal oocytes were measured. There was no effect of treatment group on any of these parameters. Results of this study indicate that female exposure to ivermectin was of greater importance than male exposure in altering male mating behaviour and reducing fecundity. Ivermectin in cattle dung could therefore lower reproductive output of this species even when only one of a pair was exposed to the drug.