Guest blog by Robyn Crowther, Digitiser
After digitising our parasitic lice, we were looking for another microscope slide collection to digitise using the same methodology, having cut down our imaging time for each slide to 14 seconds. So when the opportunity to digitise the beautiful psyllid slide collection arose, we jumped at the chance.
Digitiser Robyn has been working on the collection and tells us more about these tiny agricultural pests.
Psyllids are a relatively small group (∼4000 described species) of sap-feeding Hemiptera, an order of insects more commonly known as “true bugs”. Psyllids range from 0.8-8mm in length and can be found all over the world. Several species are agricultural pests and have a reputation for being highly host specific as they spend their immature to adult life cycle restricted to one, or a few closely, related plant species. For this reason they are very interesting for scientists to study, for instance in testing co-evolutionary hypotheses.
These agricultural pests have been digitised to help scientists better understand past, present and future threats to global food security. Mobilising the data held in the museum’s psyllid collection will allow scientists to develop a well supported case for the evolutionary history of this important pest group, which in turn, could help evaluate their current and future impact on food production.
Behaviour and impact on global food security
Psyllids are “aphid like” insects, and while they lack the infamy of the other pests in their taxonomic group – a list that includes mealybugs, scale insects, and whiteflies – the damage they cause to crops can be significant, with commonly affected plants including important food crops such as citrus fruits, pears, apples, carrots, avocado, potatoes and tomatoes.
When psyllids feed, their piercing-sucking mouthparts, common to all Hemiptera, are inserted into the food-conducting tissues of the plants, targeting the fluids rich in sugars and amino acids. This can cause considerable damage to the plant, including leaf and shoot distortion, stunted growth, and defoliation. In addition, as psyllids feed they excrete a sticky liquid known as honeydew. This liquid can lead to the development of sooty mould on leaves, preventing proper photosynthesis.
Images from https://en.wikipedia.org/wiki/Bactericera_cockerelli https://en.wikipedia.org/wiki/Zebra_chip
As well as causing direct damage by feeding, psyllids act as vectors of plant pathogens, injecting toxic salivary secretions into the plant tissue. The psyllid Bactericera cockerelli is considered one of the most destructive potato pests in the western hemisphere, vectoring diseases such as “psyllid yellows” and “zebra chip”, so called due to the black lines that appear on fried potato chips taken from infected plants. The potato is ranked as the world’s third most important food crop, meaning that psyllids that damage these crops are not only causing severe economic losses but also potentially endangering global food security.
Digitising the psyllid collection
We have added a few modifications to our slide digitisation workflow for this project including adding a barcode during imaging that encodes the country in which the specimen was collected. This information would otherwise have to be transcribed by a digitiser at a later date. By attaching the data to the specimen record as the image is created, the whole digitisation workflow is streamlined and researchers can get the important information closer to real time, with fewer errors.
The Museum’s psyllid collection is one of the most comprehensive collections in the world. It was initially thought to consist of around 14,400 slides, covering 1301 species, however, after completing the digitisation of this collection late last month, it is now know to hold 20,766 specimens covering 1100 species. Experience has shown us that the initial estimate of the size of many collections changes as the digitisation process progresses and we get more accurate data. During this project we have imaged specimens collected from every continent except Antarctica, and have found slides dating back almost two centuries. This comprehensive coverage, both geographically and temporally, makes this a valuable resource and it is only by digitising this collection that the important information held within becomes more readily available to researchers.
Museum Scientists Diana Percy and David Ouvrard are studying psyllid ecology and evolution in order to understand these important pests.
Diana Percy told us “Much has been said about climate change and its impacts, but little is known of the impact of shifting species ranges in response to environmental changes. There is an important role for museum records as snap shots through time: historic records of geographic locations and host plants that we can piece together to understand species movements, shifts in feeding habits, or disease carrying capacity. Presenting evidence for past and present correlations, cause and effect, will help raise awareness of the impacts of these changes.”
The collection provides data for mapping and niche modelling, which helps to predict the future ranges of these insects and their host plants and assess the distribution and taxonomic diversity of the psyllid fauna associated with important crops.
Scientists have also found a way to use these bugs’ powers for good. Their ability to cause significant damage to plants, coupled with their host specificity, can be used to our advantage. In recent years, the psyllid Aphalara itadori, usually found in southern Japan, has been released at several undisclosed regions around the UK in the hope that it could help to suppress the invasion of its very specific host plant, Japanese Knotweed (Fallopia japonica). Unfortunately, while initial studies showed that this psyllid is able to successfully overwinter in the UK, populations have struggled to build sufficient numbers at the release sites to demonstrate their effect on the invasive plant.
Biological control is famously tricky. However, using psyllids in this way has the potential to address two of the biggest threats to biodiversity: invasive species and pesticides. Japanese knotweed not only causes millions of pounds worth of damage to property and infrastructure but is also threatening native flora and habitats, as its aggressive growth quickly forms dense stands that exclude other plants from growing, reducing biodiversity. In addition, pesticides have been linked to the drastic loss of insect biodiversity in recent decades. Therefore, with careful research and planning, hopefully facilitated by the data we are mobilising during this digitisation project, this approach has the potential to be a small victory for conservation.
The digitisation of the psyllid slide collection is now complete! All of the images taken during this project are available on the Museum’s portal. For regular updates on digitising the museum’s collections follow @NHM_Digitise on Twitter or Instagram.