PLEASE NOTE The surveys are ongoing; updates can now be found on the hemerocallis gall midge advice profile. See our blog on the outcomes of the surveys and animated map of the changing distribution. This page is no longer being updated.
Common name: hemerocallis gall midge
Latin name: Contarinia quinquenotata
Characteristics: Hemerocallis flower buds become abnormally swollen and do not open. Caused by 2 -3mm long white maggots of the midge feeding and developing inside the buds during late May – early July.
This gall midge is widely distributed in Europe but was not found in Britain until 1989, when samples of galled flower buds were brought to the RHS Advisory Service at RHS Garden Wisley from a garden in Weybridge, Surrey. Since then the spread of this pest in Britain has been tracked through this survey and enquiries made to the RHS Advisory Service. It is now widely distributed in England, and has become established in Scotland and Wales.
Thank you to those who took part in the survey in 2008 to 2014. More than 400 records of the midge have been received, greatly adding to knowledge of this pest's distribution in the UK.
Description and life cycle
Hemerocallis gall midge is a tiny fly that lays its eggs in the developing flower buds of daylilies (Hemerocallis species and cultivars). The midge has one generation a year, with damage to the flower buds occurring between late May and early July. Cultivars that flower after that period often escape damage.
Small white maggots develop inside the buds, causing them to become abnormally swollen and fail to open. When fully fed, the larvae are 2-3mm long and they drop down into the soil where they overwinter as pupae.
An infested bud can contain several hundred larvae, which may be the progeny of more than one midge.
Late flowering cultivars of daylily are often unaffected by the gall midge. From observations made on the extensive Hemerocallis collection at RHS Garden Wisley, a list has been compiled of late-flowering cultivars that partly or wholly miss the egg-laying period of the gall midge.
Download the list of Hemerocallis less prone to damage (165kB pdf).
• None of the pesticides available to home gardeners carries a label recommendation for use against gall midges, however RHS research has shown that systemic insecticides can reduce damage if applied in late May or early June. Plants in flower should not be sprayed due to the risk to pollinating insects and sprays are not suitable for use where it is intended to use the flowers for culinary purposes. Download research report (Adobe pdf document) Read more
• Galled buds should be picked off and destroyed before the larvae are able to complete their feeding. This will reduce damage in the following year but the effectiveness depends on how thoroughly the galled bud-picking is done and whether nearby gardens also have infested plants.
• RHS Advice on Hemerocallis gall midge
Help us with research
The RHS is keen for the data to be used in further research projects and collaborations. Email us at firstname.lastname@example.org if you would like to use RHS data for research.
Data is already shared with the National Biodiversity Network.