MATING COMBINATIONS OF CONTROL AND IVERMECTIN-FED DUNG FLIES NEOMYIA-CORNICINA (DIPTERA, MUSCIDAE) - EFFECTS ON MATING-BEHAVIOR, OVIPOSITION AND OVARIAN DEVELOPMENT

The dung fly Neomyia cornicina (Fabricius) fed on either control dung or dung containing 0.15 mu g g(1) ivermectin were mated in the followi ng combinations: (a) control malexcontrol female, (b) control malexive rmectin-fed female, (c) ivermectin-fed malexivermectin-fed female and (d) ivermectin-fed malexcontrol female. Frequency and duration of mati ng attempts by males during 10 min mating trials were significantly hi gher 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 s ignificant effect of mating combination on the percentage of females t hat laid eggs, with most laying in groups where females were controls (groups a and d). There was also a significant effect of mating combin ation on the time to first oviposition, with control females mated wit h control males (group a) laying earliest. Egg batch size was unaffect ed by treatment group. At the end of the experiment, all females were dissected and the number, size and yolk content of the terminal oocyte s were measured. There was no effect of treatment group on any of thes e parameters. Results of this study indicate that female exposure to i vermectin was of greater importance than male exposure in altering mal e mating behaviour and reducing fecundity. Ivermectin in cattle dung c ould therefore lower reproductive output of this species even when onl y one of a pair was exposed to the drug.