Validation of fluorescent dust marking of Culicoides biting midges and the design of a self-marking technique

Background: Investigation of insect flight patterns frequently involves the use of dispersal studies. A common method for studying insect dispersal is mark-release-recapture (MRR) techniques using wild-caught insects in their natural environment; however, this requires a suitable marker. At present, no studies have been performed to identify markers that are suitable for use in midges within the Obsoletus Group, and visible by eye or down a light microscope. Methods: A series of 11 experiments were undertaken to determine the effectiveness of three colours of Brilliant General Purpose (BGP) fluorescent dusts in marking Culicoides midges. Three areas were focused on: 1) dust properties, 2) the effect on Culicoides, and 3) dust application in the field. Results: All three dusts were insoluble in water, 10% washing-up liquid and 70% ethanol. They were visible down a microscope, with and without the use of a black light, and two were highly visible without the need for a microscope. The dusts remained adherent to the marked Culicoides for the duration of the experiments, did not transfer between marked and unmarked individuals or the environment, and remained adherent when the Culicoides were stored in an ethanol or water-based solution. The dusts had no effect on the mortality rate of the insects over the 48 hrs of the experiment. There were no significant differences between the recorded behaviours undertaken by undusted control Culicoides and the BGP fluorescent dusted Culicoides. Field-based marking of Culicoides can be achieved using a 'self-marking' technique, whereby the trapping vessel is pre-dusted with fluorescent dust prior to trapping the individuals to be marked. Conclusions: This is the first study to identify BGP fluorescent dusts as markers for use with Obsoletus Group Culicoides. BGP fluorescent dusts provide a quick and effective method of marking and identifying Culicoides for both field and laboratory studies. The self-marking technique minimises the time needed to handle specimens prior to release.