SLU news

The gout fly - a new pest of spring wheat

Published: 11 June 2024
A fly on a green leaf. Photo.

The gout fly came to southern Sweden in 2019 and damages spring wheat. Hanna Kollberg has compiled information about the biology, damage and control of the corn fly in Sweden in her bachelor's thesis.

The gout fly (Chlorops pumilionis) is a relatively new insect pest in Sweden. The first serious attacks by gout fly on fields of spring wheat were observed in Skåne, Blekinge and Halland in southern Sweden 2019. Since then, the gout fly has become an established pest and has also occurred in some places in central Sweden.

– The purpose of my essay was to summarize the biology of the gout fly, its
damaging effects and possible control measures in Sweden through a literature review, as well as to identify gaps in knowledge and possible areas for continued research, says Hanna.

Barely and triticale under attack

Several species of grass act as host plants, but among the cereal crops wheat, barley and triticale can be attacked by the fly. Barley and oats are never or rarely attacked. However, spring wheat is the crop most sensitive to significant damage. Attacks in winter wheat are also relatively common, but winter wheat is usually able to compensate well for the damage and attacks usually do not affect the final harvest.

The gout fly has two generations per year. The adult flies of the spring generation hatch from their pupae in May – June and lay eggs on spring grain. The adult flies of the autumn generation hatch in July – August and lay eggs on autumn grain. It is the larvae of the gout fly that cause damage by gnawing on the plant, but the damage differs between attacks on autumn grain and spring grain.

– The spring larvae cause stunted length growth and damage to the ear which may become deformed and remain in the leaf sheath. Autumn larvae enter the shoot base to overwinter, causing swollen shoots that die in spring when the larvae pupate, says Hanna.

Natural enemies of the gout fly larvae

There are two species of parasitoids that attack the gout fly larvae, Stenomalina micans and Coelinus niger. Preventive control measures that can be used are adapted sowing time, cultivation of resistant cultivars, control of alternative host plants and fertilization to favor growth and development. Spraying with the pyrethroid Nexide can be used as direct control, and control recommendations from the Swedish Board of Agriculture are available for winter wheat and spring wheat.

Chemical control against the fly in winter wheat is rare, but may be warranted if there has been a heavy infestation in the area in previous years and if there are eggs on more than 50% of the plants when they are in the 1–2 leaf stage (DC 12). In spring wheat, there is no control threshold at all.

– The knowledge gaps and areas for future research in Sweden that have been identified concern the gout fly's life cycle, the role of the natural enemies and their distribution and biology, resistant cultivars and the development of more extensive control recommendations for chemical control, concludes Hanna.