The phenology and pollen feeding of three hover fly (Diptera : Syrphidae) species in Canterbury, New Zealand

The phenology and sex ratios of three hover fly species on Canterbury farml and, New Zealand were recorded weekly from five yellow water-traps from Oct ober 15, 1993 to January 31, 1997. Gut fullness, egg number and pollen cont ent were recorded weekly from September 8, 1994 to July 25, 1996. Catches o f Melanostoma fasciatum (Macquart) and Melangyna novaezelandiae (Macquart) were higher during the summer months, with maximum male M. fasciatum catche s at 0.7 per trap/day in January, 1997. Catches of female Eristalis tenax L . peaked at 0.24 in August, 1994. Gut fullness and egg number in M. novaeze landiae and M. fasciatum were low from June to September, 1995, a pattern o pposite to that off. tenax. For all species combined, gut fullness was sign ificantly higher in gravid females compared with non-gravid females, and ma les. Thirty-nine different pollen types were recorded from all hover fly cl asses. Male E. tenax (the largest of the three species) consumed the widest range of pollen in summer and autumn whereas females consumed the widest r ange in winter and spring, a pattern opposite to that of M. novaezelandiae. The value of the work in possible population enhancement programmes for ho ver flies in crops is discussed.