Description and biology of agapanthus gall midge

RHS project team

Hayley Jones and Andrew Salisbury

Partners

Keith Harris, Agapanthus Trial Forum

Start date

02/07/2014 00:00:00

End date

30/06/2016 00:00:00

Keywords

Agapanthus, gall midge, Cecidomyiidae, lifecycle

The problem

The agapanthus gall midge is a new undescribed pest affecting Agapanthus that belongs to the Cecidomyiidae family of flies. The tiny gall midge lays eggs which develop into maggots inside the individual flower buds or inside the closed flower head sheaths. The maggots can then cause the bud to be deformed and discoloured and often fail to open. The severity of this can range from a couple of buds failing, to collapse of the entire flower head. Infestation can be confirmed by opening the buds or flower heads and looking for the presence of small maggots 1-3mm in length which are a creamy yellow or orange colour. Symptoms and larvae can be seen in the images below.

This problem was first noticed in a private garden in 2014 and brought to the attention of entomologists at the Royal Horticultural Society. Inspection at RHS Garden Wisley showed it was present in the RHS collections and subsequent reports indicate it has been present in the UK for at least two years and it is widely established in other parts of southern England. The species responsible has not been previously described in the UK or abroad; although there is some evidence a midge can also cause damage to agapanthus in South Africa.

Consequently, very little is known about the biology and lifecycle of this insect and so the Plant Health team at RHS Garden Wisley have launched a project to study it, working with Defra and international experts.

Defra have added the agapanthus gall midge to the UK Plant Health Risk Register and are considering what actions are appropriate to manage the incursion of this pest. One of the likely actions is a targeted survey and awareness raising to help determine the distribution of the midge and scope for actions to mitigate impacts.
 

Symptoms (low) - click to enlarge
Symptoms (medium) - click to enlarge
Symptoms (severe) - click to enlarge
Affected buds - click to enlarge
Larvae - click to enlarge

Approach

The Plant Health team is investigating the midge so that control advice can be provided. First the species must be described and assigned a scientific name – this work is being carried out in collaboration with Keith Harris, an international expert on cecidomyiid flies.

Many samples of larvae from different locations will be gathered to extract DNA for sequencing so that we can deduce how this midge is related to other Cecidomyiidae such as the hemerocallis gall midge (Contarinia quinquenotata).

Observations are being carried out in summer 2015 on plants at RHS Garden Wisley and on infested plants that are contained within the RHS Field Research Facility. This will enable preliminary study of the biology and life cycle of the midge and description of the appearance of all life stages.

Further experimentation and observation will be carried out in 2016 with midge populations reared through from live samples from 2015. This may include a replicated experiment on pesticide application to assess timing and products appropriate to achieve some level of control. We will also be looking for the emergence of natural enemies such as parasitoid wasps.

Project update

RHS scientists in collaboration with Keith Harris published a description of the midge species in 2016, it now has the scientific name Enigmadiplosis agapanthi. A report outlining the results of observations on the midge’s biology and lifecycle made in 2015 can be found here.

Following a pest risk analysis and due to the widespread distribution of the midge Defra decided that statutory action was inappropriate. This means that as the pest is unlikely to be eradicated, commercial growers and home gardeners will need ways to manage it. Therefore the RHS decided to apply for funding from the Agriculture and Horticulture Development Board to continue research into the biology of this midge and start to find some control options. This project is being carried out in collaboration with ADAS.

Further information

Agapanthus gall midge advice profile page
End of season 2015 report
Species description

Aims

Request for observations
Gardeners are requested to help us map the spread of the midge in the UK by sending in photographs of infested flower heads to [email protected]. Photographs showing symptoms plus opened buds where the small larvae are visible will help make the record more certain. 

Please include the postcode of where the plant is growing as well as any information about cultivar name, date of planting and place of purchase if known. 

Please note: due to the ongoing Covid-19 situation, please do not send samples as we are currently unable to examine them.

Benefits to gardeners

The RHS will be able to accurately diagnose and provide advice for gardeners about the agapanthus gall midge. We will be able to ascertain the host plant specificity of this novel insect to the UK and understand enough about its biology and life cycle to suggest appropriate measures of control.

Further information

Agapanthus gall midge advice profile

End of season report - 2015