Dimethyl trisulphide is a strong attractant for some calliphorids and a muscid but not for the reindeer oestrids Hypoderma tarandi and Cephenemyia trompe

A field test with synthetic dimethyl trisulphide as attractant in flight traps was carried out in Finnmark, northern Norway, in July 1992 and 1994. The reindeer oestrids Hypoderma (=Oedemagena) tarandi (L.) and Cephenemyia trompe (Modeer) (Diptera: Oestridae), previously shown to react positively to dimethyl trisulphide on the olfactory receptor level, were only caught in small numbers, with no significant differences between baited and unbaited traps. In both years, however, the baited traps caught significantly more individuals of Calliphoridae and Hydrotaea anxia (Zetterstedt) (Diptera: Muscidae) than unbaited control traps. In 1992, Protophormia terraenovae (Robineau-Desvoidy) (Diptera: Calliphoridae) and H. anxia were the predominant species (78.5% and 20.5%, respectively). In 1994, H. anxia was the most prevalent species (73.6%). Seven species of Calliphoridae were caught, with P. terraenovae, Calliphora vomitoria (L.), C. uralensis (Villeneuve) and C. loewi (Enderlain) as the most numerous ones. Dimethyl trisulphide is probably a decomposition product from bacterial activity and may be one of the major cues for calliphorid host finding. The significance of the reaction for oestrids on the receptor level, but evidently not on a behavioural level, remains unclear.