...and now for something completely different

...the agapanthus gall midge!

At the RHS I work on two main groups of garden pests, and they are very different experiences! The first is gastropods – slugs and snails, and these are the oldest problem in the book. Everyone knows what they are and has probably wrested with them in their own garden. By contrast, my other research is on the agapanthus gall midge , which was new to science when it was first discovered in the UK by the RHS, in 2014.

Unlike slugs and snails this pest only affects one plant – Agapanthus. The midge lays its eggs on the flower buds and the larvae grow and feed inside, so that rather than opening into a beautiful flower the bud turns into a gall. This doesn’t harm the plant as the midge only feed on the flowers, and Agapanthus spreads mostly vegetatively, but as this plant is grown in the UK purely for its ornamental value the disfiguring of the flowers is a real problem for people who love the plant! There are lot of people in the UK that really love Agapanthus, and growers that specialise in it, so we are studying this midge and hope to find means to keep it under control.

Agapanthus gall midge symptomsAs a scientist my first activity when starting a new research project is to read all of the literature currently available on the topic, to get a good base of knowledge and to see what experiments others have already done. However because the insect is new to science there wasn’t any documentation on it, except a possible mention in a South African gardening book on Agapanthus.

Luckily a former RHS entomologist, Keith Harris, is an international expert on Cecidomyiidae flies (gall midges) and still lives near Wisley. This meant I could work with him to learn about gall midges in general and figure out which lifecycle traits our new midge was likely to have. His expertise meant that he could study and compare the morphology of the adult flies and the larvae to other gall midges, and write a description of the species, giving it a scientific name: Enigmadiplosis agapanthi.

Click to enlarge: agapanthus gall midge distributionMy mission for the past two years has been to observe the activity of the midge in RHS Garden Wisley and rear it under lab conditions. From this I have been able to deduce information about how long the midge is active outside, how long it pupates for, what parts of the plant the larvae can live in and some initial ideas about whether it has preferences between different cultivars of Agapanthus. I have also collated observations of the midge from RHS members and the public, to create a map of the current UK distribution. This shows that the midge is already pretty widespread, and is probably here to stay! The results of my work in 2015 can be seen in this report.

In 2016 I wrote a project proposal for funding from the Agriculture and Horticulture Development Board, in collaboration with ADAS and professional Agapanthus growers. This was successful and will give us more funding to study the biology and lifecycle of the midge, and also to start trying to find some methods to control it.

It has so far been challenging but satisfying to work on an organism where there is no prior knowledge. It can be hard to know where to start, and experiments can fail because of lack of basic information. However every bit of understanding I discover is a real advance, and will help growers and gardeners to manage this new threat.


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