Biology and control of agapanthus gall midge – AHDB funded project

RHS project team
Hayley Jones
Jude Bennison, ADAS AHDB (The Agricultural and Horticultural Development Board)
Start date
01/07/2016 00:00:00
End date
30/06/2017 00:00:00
Agapanthus, gall midge, Cecidomyiidae, lifecycle, Enigmadiplosis agapanthi
The problem
The agapanthus gall midge (Enigmadiplosis agapanthi) is a recently described fly whose larvae live and feed inside developing flower buds of Agapanthus, causing them to become deformed and discoloured and often fail to open. Further information on the background behind this insect can be found on the RHS web profile.

As this pest has only recently been described (previously new to science) there is very little information on its biology available, and no research into control methods has been carried out. Initial research into the biology of the midge was carried out by the RHS in 2015 and the species description was published in 2016 in collaboration with Keith Harris. Subsequently a project proposal was submitted to the AHDB who awarded funding for this project.
This project consists of four main objectives:

     1. Determine and describe the life cycle of agapanthus gall midge

This will be done by gathering larvae from infested sites in the UK and rearing them, enabling all life stages to be observed and duration of different life stages to be recorded.

     2. Confirm the distribution and host range

The UK distribution of the midge will be determined by a call to the public for records. See information on how to submit an observation. Information on worldwide distribution will be gathered by a survey from the International Plant Sentinel Network.

A preliminary study of cultivar preference will be carried out to see if some of the more widely grown cultivars of Agapanthus are preferred as hosts by the midge.

     3. Quantify the effectiveness of potential chemical and biological controls

A number of chemical and biological controls will be tested for effectiveness in two different laboratory experiments:

A. As drenches or incorporated into growing media in small pots. Larvae will be added to these pots to simulate them dropping to the ground after feeding in a flower. The number of adults successfully emerging from these pots will then be counted.

B. Sprays of chemical and biological controls will be applied to infested flower heads (which will be housed as cut stems in vases of water). After two weeks the numbers of dead and living larvae inside the flower heads will be counted and traps below the flower heads will be used to count fully grown larvae leaving the flower to pupate.

We will also set up a field site of 160 Agapanthus plants in 5 replicate blocks in simulated nursery conditions, which will have infestation pressure applied by introducing infested flower heads to the area. In subsequent years we will use this to test any control methods that perform well in the laboratory tests.

     4. Communicate the results to the industry

The results of this project will be communicated to Agapanthus growers through the AHDB Grower magazine and at AHDB events. Updated advice for home gardeners and the general public will be communicated via the RHS website and The Garden magazine.
Benefits to gardeners
Improved diagnosis and advice for gardeners on control of agapanthus gall midge. Biology and control information will also help commercial growers, to provide uninfested plants for sale.
Further information
See also - RHS projects on plant pests

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