Effect of avermectin residues in sheep dung on mating of the Australian sheep blowfly Lucilia cuprina.

Male and female Lucilia cuprina adults were separated after emergence and then fed either dung excreted from sheep after an oral treatment with ivermectin (Ivomec) or non-treated sheep dung. Fresh dung (non-treated or ivermectin-treated) was collected daily and fed to adults for 6 days after drenching. After this feeding period, males and females from each feeding treatment were paired and all aspects of mating behaviour recorded. Feeding on avermectin residues by adults had a significant effect on two components of mating: (1) males fed on ivermectin-treated dung directed less mating attempts at females compared with males fed on non-treated dung; (2) mating duration by males fed on ivermectin-treated dung was longer compared with males fed on non-treated dung. There was no significant difference in the level of sexual receptivity (percentage mating) between females fed on either ivermectin-treated dung or non-treated dung, although subsequent oviposition by females fed ivermectin-treated dung was significantly delayed. Both female and male mortality was significantly greater when feeding on ivermectin-treated dung compared with non-treated dung. The effects on mating, when coupled with the deleterious effects on ovarian development and adult mortality, demonstrate the potential for avermectin usage in a control strategy against L. cuprina.