Agapanthus gall midge is a fly that can cause buds of Agapanthus to become deformed and discoloured and fail to flower. It was first noticed in the UK in 2014 but may have been present for several years.
A bud is a small, undeveloped shoot that contains the potential for new growth. Buds are typically found on stems, where they can be apical (found at the tip) or axillary (found between leaf axils) and may develop into leaves, shoots or flowers.
Until 2016 the species of midge causing this problem was undescribed (i.e. new to science). Consequently, very little is known about the biology and lifecycle of this insect. The Plant Health team at RHS Garden Wisley have been studying the midge since its discovery in 2014, and are asking for help from gardeners who have seen agapanthus gall midge or damaged flowers.
Please send photos of symptoms on the flowers and buds, plus opened buds showing larvae where possible, to entomology@rhs.org.uk. Please include postcode of location of the plant, to help us to map how widespread the midge is in the UK. In previous years we have asked for samples to help with research; many thanks to those who have contributed these have helped further our understanding of the midge. We no longer require large quantities of material so please do not send samples unless individually requested.
Submissions to our pest and disease surveys are stored permanently in an anonymised form in order to monitor the spread of the pest or disease. We may contact you within 2 months of your submission in order to verify your sighting but your personal data will not be permanently stored in connection with your submission and will be deleted after 1 year. We publish and share only non-identifiable data from survey submissions (such as a six figure grid reference) with third parties and the public for the purposes of scientific research and advancing understanding among gardeners.
If the foliage of Agapanthus appears healthy but the flowers are abnormal in the ways described below, then agapanthus gall midge is most likely the cause:
Currently management strategies attempt to interrupt the insects life cycle:
The RHS has been researching potential cultural, biological and chemical controls and this has directly informed the advice given above. The results of the most recent project, completed in collaboration with ADAS and funded by the AHDB can be downloaded from: https://horticulture.ahdb.org.uk/development-of-novel-control-options-for-agapanthus-gall-midge-2
The tiny gall midge lays eggs on the plant and the larvae develop inside the individual flower buds, inside the flower head sheath or in the petals of flowers that have gone over. The larvae can then cause the bud to be deformed and discoloured and often fail to open, as their feeding activities convert the plant material into a gall. The severity of the damage can range from a couple of buds failing to collapse of the entire flower head.
The presence of the gall midge can be confirmed by opening the buds or flower heads and looking for the presence of small maggots 1-3 mm in length which are a creamy yellow colour. The midge larvae leave the flower head to pupate in the soil, which takes around ten days. It is likely that they also overwinter in the soil and pupate the next spring.
The larvae can live in any stage of flower development, including in senesced flowers. Larvae can most commonly be seen inside individual flower buds, but if infestation occurs before the flower head sheath opens then the larvae can live and feed between the developing flowers and cause complete failure of the flower head.
Our research so far has shown that there may be multiple overlapping generations of the midge, as active larvae have been seen between mid-June and early October. So far no treatments have proven effective at targeting the larvae in the flowers. This is unsurprising as they develop inside the plant tissue and the long active period of the adults makes targeting egg-laying females difficult. The underground pupation and overwintering life stage is likely to be the most useful target for control.
Protect your garden RHS Science: Agapanthus gall midge species description RHS Science project: Description and biology of agapanthus gall midge RHS Science project: Biology and control of agapanthus gall midge
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