A guest blog by Robyn Crowther
The Digital Collections Programme is digitising the Museum’s scale insect collection. This collection is estimated to contain 100,000 microscope slides, making it the biggest slide digitisation project we’ve undertaken so far.
We are digitising this collection using the slide digitisation workflow, an established workflow that has been fine tuned during previous projects to digitise the Phthiraptera and Psyllid slide collections. We now capture more data about each specimen and have achieved some of our highest rates of digitisation, 2174 specimens digitised in a single day!
Ranging in length from 1 – 25mm scale insects (Superfamily Coccoidea) may be small, but the damage they cause to crop plants can be mighty. They belong to the Order Hemiptera, or “True Bugs”, a taxonomic group that contains some big names in the crop pest world: Aphids, Mealybugs and Psyllids. The characteristic that scale insects share with their pesky relations is that they all possess sucking mouth parts. They use these to pierce a plant’s vascular system or other cells, from which they can suck the sugar-rich sap that flows there. This causes damage including wilting and yellowing or death of leaves, and a stunted and unhealthy appearance. Many plants that these bugs feed on are important crops, including grapevines, coffee, citrus and olive trees. Damage caused by scale insects not only leads to significant economic loss but can also affect food security at a national and international level.
Adult female scale insects cover themselves with waxy secretions, sometimes forming a protective scale cover. Species from the family Diaspididae (known as Armoured Scales) make a hard, shield-like cover composed of shed skins and wax that conceals, but is not attached to the body of the insect. In contrast, soft-bodied species of scale insect only produce a thin, cottony or waxy covering that is attached to the body.
As hard as scales
As well as causing direct damage to their host plants by extracting nutrients and injecting toxic saliva, scale insects can cause indirect damage by excreting copious amounts of sugary honeydew, a sticky mixture of undigested sugar and water that passes through the insect’s digestive system and is deposited on nearby surfaces. This supports the growth of a black fungus called Sooty Mould, which blocks light and air from the leaves, inhibiting photosynthesis, reducing the commercial value of the plant or its produce by up to 50%.
A Cottony Cushion Scale (Icerya purchasi) vs. an Armoured Scale (Saissetia coffeae)
The Darwin Initiative
The damage caused by scale insects is particularly great in Kenya. According to current estimates, 29% of all scale insect species recorded in the country are potential crop pests; this is significantly higher than in any other group of insects. Recent outbreaks of invasive scale insects, such as the coffee mealybug (Planococcus kenyae) and Papaya Mealybug (Paracoccus marginatus), have caused crop yield losses of up to 91%, putting the livelihood and food security at risk. To control these outbreaks, large-scale indiscriminate pesticide application takes place. This actually exacerbates the problem by killing beneficial organisms such as natural enemies and pollinators. Targeted biological control is the best way to combat these pests; however, it requires accurate identification of the scale insect species.
The Darwin Initiative is a UK government grants scheme that helps to protect the environment through locally based projects worldwide. As part of the Darwin Initiative, Museum scientists are providing taxonomic training and scale insect identification aids to local communities to enable better pest management practices.
Museum scientist Dr David Ouvrard, describes some of the work done to address scale insect threats in Kenya:
“Fourteen Kenyan trainees have been trained to collect and preserve specimens from the field and were familiarised with useful taxonomic characters for identifying scale insects. So far, two new continental records for Africa have been found, and new Kenya records for one family and 52 species, seven of which are new to science. This illustrates the current poor knowledge of the Kenyan scale insect fauna, and of threats presented by alien introductions.” Read more about the work being done to address the scale insect threats in Kenya at https://www.darwininitiative.org.uk/project/25032/
This project inspired the Digital Collections Programme to digitise the whole of our scale insect collection, which contains specimens collected from all over the world. By sharing this vast amount of data openly on our Data Portal, we hope to aid further research into the development of efficient pest management strategies that can help people and the environment.
Simply the Pest?
While scale insects are pests that are capable of destroying crops, there are some farmers that encourage scale insects to live and grow on their land. This is because the scale insects themselves can be harvested for use in a range of everyday products. Below are a couple of examples of where you may have unwittingly encountered these bugs.
Natural Red No. 4
The red dye, Carmine, is derived from Cochineal. Cochineal is made by drying and pulverising the scale insect Dactylopius coccus, whose body, under its white, waxy coating, is a rich, raspberry colour. This natural colouring, also known as Carminic acid, Natural Red No. 4, or E120 is widely used in the food industry to colour a range of products from frozen meat and fish (ever wondered where the vivid red of the generally mysterious “seafood” sticks comes from?), to yoghurt and ice cream.
The next time you’re admiring your manicure, taking an aspirin or enjoying a jelly bean, spare a thought for the scale insect Kerria lacca. Kerria spends its short life sucking up sugary sap and producing lac, a resinous excretion, in an almost constant process. The lac solidifies into a hard protective shell that can be harvested, forming the basis of shellac. Shellac is widely used as a furniture finish, but it is also found in a range of cosmetics including nail polish, mascara and hairspray. Shellac is also used to create “Confectioners glaze” or food additive E904, which adds a shine to a variety of sweets, as well as oranges, lemons and apples. Add to this the fact that almost all tablets are coated in pharmaceutical grade shellac to allow distasteful medicine to be swallowed and to stop them dissolving too quickly in the harsh conditions of our stomach and intestine, and it is very likely you have recently consumed the secretions of a scale insect!
We are currently just over half way through the collection. However, it is not until the whole collection is digitised that we can accurately say how many slides it contains and exactly what the geographic and temporal spread of the collection is. What is known for certain however, is how important it is to share the data held in our collections with the scientific community and the public:
“The Museum scale insect collection contains many unpublished distribution and host-plant species records. Making images of the slides will make this valuable data available to researchers, increasing our knowledge and understanding of where pest species occur and what crops they attack. Our present project is documenting the Kenyan fauna but there are many other countries where the fauna is undocumented, so the images will provide data for many similar projects in the future.”
Dr Gillian Watson, a researcher at the museum working on the Darwin Initiative project.
Unlocking the Museum’s collections and making them available to all is the mission behind many of our digitisation projects and is one of the Museum’s strategic priorities. There are over 1.5 billion natural history specimens in collections around the world that have the potential to play a critical role in addressing the most important challenge that humans face over the next years: how to map a sustainable future for ourselves and our changing planet. To see the scale insects digitised during this project, and over 4.4 million other specimens, visit the Museum’s Data Portal.