Blowfly (Diptera, Calliphoridae) damage on stockfish in northern Norway: pest species, damage assessment and the potential of mass trapping

Production of high quality stockfish in northern Norway takes place from February to May. The dominant blowfly species (Diptera: Calliphoridae) with adults present during stockfish production were Calliphora vicina and Protophormia terraenovae. Larval collections identified the damage-causing species to be C. vicina. Other saprophagous blowfly species were only found after the production period. Fish dried in sun-exposed locations experienced more damage than fish in shaded locations, and the risk of damage was higher in fish dried later in the production period. Yellow sticky traps and funnel traps baited with dimethyl trisulphide were tested for their potential in mass trapping. Sticky traps caught flies during early spring, while funnel traps increased in efficiency closer to summer. Attraction to dimethyl trisulphide was found to be significantly higher for C. vicina compared to P. terraenovae, and the catch of C. vicina consisted of 92% females. The catch of female flies during the critical drying period consisted of 5–30% of the estimated number of flies having caused damage. The target specificity with high female catches and the cost efficiency of these traps indicate that mass trapping can be used as an integrated part of a management program to reduce damage from blowflies in stockfish producing areas.