Gall midges
Gall midges are mostly very minute flies. Most species are between two and three millimeters long, and the smallest measure less than a millimeter. Although small, they have a significant ecological effect on their environments. Most gall midges develop in plants, and many species form galls, i.e. malformations of the host plant that provide nutrients and protection for the larvae. Gall midges are usually highly host-specific. Each species usually attacks only one or a few plant species, and only uses a specific part of the plant. Many gall midges attack agricultural crops, and several species are serious pests in agriculture. Some gall midge groups do not feed on plants, but are either fungivores, decomposers or predators. Some predatory gall midges are used for biological control in agriculture. Two such species are Aphidoletes aphidimyza, which preys on various species of aphids, and Feltiella acarisuga, which preys on spider mites. The genus Lestodiplosis contains many species that are predators of other gall midges.
About the project
The Gall Midge Project (Gall Midges Phase II) is part of the Species Project. The main project goal is to gain more knowledge about the gall midge fauna in Norway, with particular focus on the plant-feeding species. The project builds on a previous project, Gall Midges Phase I, which ran from 2019 to 2022. In that project, 93 species of gall midges new to Norway were discovered (Elven et al. 2024). The project also collected a very large amount of material that has not yet been processed. In Phase II, we will mainly continue processing this material and identify, DNA barcode, photograph and make microscope slides of specimens from several hundred midge samples. We will also supervise students, as well as arrange a course on herbivorous insects in collaboration with BIOCORE. The project also includes a sub-project that specifically targets gall midges that are agricultural pests, and a sub-project where we will analyze and compare Norwegian and Finnish DNA barcoding data.
Agricultural pest species
NHM and NIBIO will collaborate to study agricultural pest midges. The goal is to collect some of the most destructive gall midges in agriculture, and at the same time document the damage/galls, the different life stages and any accompanying species. The image material and the ecological data we collect can be used, among other things, to produce information material about pests and in research on pest control. The species will be DNA barcoded, and we will build a reference collection of pest species that will be shared between our two institutions.
DNA barcodes
NHM and the University of Oulu will collaborate to analyze and compare DNA barcoding data from Norway and Finland. The University of Oulu has produced a very large dataset of DNA barcodes from Finnish gall midges. The barcodes are from adult midges that have been collected using malaise traps at locations all over Finland. NHM has a smaller dataset derived from larvae and adult midges collected from plants in Norway. This dataset will grow considerably larger during Phase II. Our plan is to combine the two datasets in a joint phylogenetic analysis. The results of this analysis will hopefully provide much new insight into the shared Fennoscandian gall midge fauna.
Collection and hatching
Gall midges can be collected in several ways. The most common methods are malaise trapping, sweep-netting in the vegetation, and collecting and hatching from infected plant material. In this project, we use the latter method. Plant material with or without visible signs of gall midges is collected and examined more closely in the lab. Gall midge larvae and/or pupae in the material are carefully extracted and transferred to alcohol. If there are enough larvae/pupae in a sample, some of them are used to try to hatch the adult midges as well. The hatching containers consist of transparent drinking cups with soil in the bottom. Both galls, larvae and adult midges are photo documented during the process. A single sample will often contain more than one midge species. In addition to the galler itself, the sample may contain inquilines (species that inhabit the galls of other species), predatory gall midges, or decomposers that often move into older, abandoned galls. All of these can in turn be hosts for various species of parasitic wasps, which are also preserved in the project. All material is secured in 80% ethanol and stored at -20°C to preserve the DNA for genetic analyses.
