Indirect study of Irish insects via novel environmental DNA sources

In early 2019, it was reported that global insect biodiversity was declining by up to 40% with one third of these species being classed as endangered. This has been largely influenced by climate change and signifies the beginning of the Earth’s sixth mass extinction event. Insects are pivotal to life on Earth as they aerate soil, pollinate plants as well as controlling pests. These contributions are otherwise known as ecosystem services.
However, insects can also be a cause of concern. There are currently 3500 known species of mosquitoes (Order: Diptera; Family: Culicidae) worldwide. Across Europe, cases of mosquito borne diseases (e.g.: malaria, dengue and West Nile fever) have been recorded. These outbreaks have been associated with changes in climate, land use, urbanisation and agricultural practices. The increased mobility of the human population and movement of goods worldwide has also furthered the globalisation of these outbreaks which increases the potential of widespread transmission of vectors and associated pathogens. Observed increases in temperature may also provide more favourable conditions for the establishment and subsequent spread of mosquitoes.
In 1991, an Irish checklist of mosquito species was compiled where 18 species were recorded. However, this is fewer than the number of confirmed mosquito species present in Great Britain (36 species), and it is probable that the Irish checklist is outdated.
To overcome issues surrounding misidentification and under-representation, molecular approaches to identify insects from their surrounding environments can be employed. The isolation of environmental DNA (eDNA) can be used as a viable option to assess insect diversity.
DNA metabarcoding facilitates the simultaneous and unambiguous identification of multiple taxa/species from a single DNA extract and can be applied to environmental samples. In this study, DNA metabarcoding was applied to faecel pellets originating from an insectivorous bat species called the lesser horseshoe bat (Rhinolophus hipposideros). The dominant (most abundant) prey groups revealed in the diet were Diptera and Lepidoptera, with Hymenoptera, Coleoptera, Neuroptera and Trichoptera also identified. Pest species such as mosquitoes (Culiseta spp., Culex pipiens) and midges (Culicoides punctatus) implicated in the spread of disease were also detected, highlighting the role of R. hipposideros in the provision of ecosystem services relevant to human and animal health.
Real-time PCR assays are currently being developed and optimised to specifically identify mosquito species by firstly testing the assay specificity and efficiency using DNA samples from known species, and subsequently applying these to environmental samples such as bat faeces and water from various sources to specifically target these species of interest.
The combination of these molecular techniques can be used to monitor insect distribution and diversity in addition to their responses to environmental alteration, such as climate change, agricultural intensification and urbanisation. Previous studies have indicated that changes in landscape use contribute heavily to diseases transmitted from animals to humans (i.e. zoonotic disease). Therefore, through monitoring insect diversity change and mosquito presence in Ireland informed mitigation measures can be instilled in advance of any potential zoonotic outbreak.