Biometeorologist forecasts aphids and plant pathogens

Biometeorologist forecasts aphids and plant pathogens

29 May 2018

“Beep, beep! Bird cherry-oat aphids will reach your area within the next six hours.” Farmers receive the alert to their mobile phones and are able to carry out prevention measures at the right place and time. As a result, delicate farmlands are protected from aphids that migrate in search of sap and spread plant pathogens.

A mobile app like the one described above could be designed based on the model developed by Finnish Meteorological Institute researcher Pilvi Siljamo in her project funded by the Academy of Finland. Instead of predicting the weather for Finland or Europe, the model forecasts pest insects and plant pathogens. Both of these problems cause significant material and financial destruction to agriculture and forestry.

The project’s mobility period abroad took place at the University of Worcester in the UK. The hills overlooking Siljamo’s home town of Malvern stand at 425 metres. Photo by Pilvi Siljamo

Climate change highlights the need for forecasting pest insects

Climate change highlights the need for identifying when and where pest insects and plant pathogens are travelling. In addition to bird cherry-oat aphids, Siljamo’s research focuses on the Alternaria genus of mould spores, a major plant pathogen and allergen. A secondary area of her research is the invasive harlequin or Asian ladybird beetle, which is a predator of both aphids and indigenous ladybirds.

“Particularly during the early summer, pest insects that arrive from the south and over long distances can catch the local agriculture and forestry industries unawares.” Accurate forecasts could serve to put an end to unnecessary pest control and improve monitoring in sensitive farmlands.”

Siljamo is also motivated by a scientific interest characterised by her outlook on academia from the viewpoint of physics: is it possible to imitate living nature through mathematical and physical models, no matter how small the brains of the objects under study?

Methodology: the atmospheric dispersion model, weather forecasts and data on insects

Insects and spores do not begin their airborne migration at random; instead, their migration follows the patterns of their area of distribution and particular circumstances.

“What’s needed is a map of the local area. In the case of bird cherry-oat aphids, this means a map of the distribution of birches, which currently coincides with the distribution of bird cherries. The development and instance of take-off of aphids is estimated based on the estimated accrual of heat summation for the area.”

This information is provided as the “emission source” and “emission date” for the Meteorological Institute’s SILAM dispersion model, which describes the travel of atmospheric particulate matter, wild-land fire smoke and radioactive materials. The model predicts the movement of cloud masses from the same data used by meteorologists to compile weather forecasts. In this project, the crucial elements are winds, rain and air humidity, as these influence the duration that spores and insects remain airborne. When the model estimates that aphids are ready for take-off and weather conditions are favourable, it can forecast the dispersion of aphids and their exit from the atmosphere.

Harlequin ladybirds were included in the model at the encouragement of British researchers. Pictured here are Pilvi Siljamo and Kate Ashbrook. Photo by Mark Cook

“The results of the model are compared against data. Data are collected from pollen and insect traps as well as by a weather radar that measures the echoes created by insects to reveal the direction of their travel and their vertical dispersion. Observations recorded in various systems by farmers and insect watchers are also useful,” Siljamo explains.

A modeller’s tool is the computer

Siljamo says that outwardly her daily work appears dull: “All I do is sit in my office and stare at a screen.” She became acquainted with computer monitors already in her first summer job in aviation weather forecast at Helsinki Airport. After this, chance and her studies led her to the world of weather and dispersion models.

The work of a modeller involves developing and testing models and processing data. Data are collected, requested and searched from a multitude of sources and converted into a usable format. After this, the model is programmed, coded and scripted. And, if at first you don’t succeed, try again.

How to simulate the movements of aphids: The weather model produces information used to calculate both the temperature sum and the dispersion of aphids. Bird cherries, the host trees of bird cherry-oat aphids, are replaced by a map of birches. The take-off and travel of aphids and their exit from the atmosphere are calculated in SILAM. The result is the current distribution of aphids in the atmosphere at intervals of one hour, for example. These maps can then be used to issue a warning on bird cherry-oat aphids.

“As an analogy, although it’s exciting to walk on the moon, the journey over isn’t particularly comfortable,” Siljamo says. A great deal of perseverance is needed before the exciting phase begins. The goal is to develop a model that can be reliably used in forecasts, but in theory, the task is endless: a model of the natural environment can always be improved to be more realistic and to cover more species.

The Academy-funded project is the global first of its kind

The pest insect warning system developed in the project is unique in the world. Instead of statistical analyses, it is based on an atmospheric dispersion model. The model is also developed for daily operative use and to cover all of Europe. According to Siljamo, the release and dispersion of mould spores have not been previously studied with the help of atmospheric models.

She also has some experience in “world-firsts”: Siljamo was among the first to combine biology with the SILAM model to produce a forecast of the long-distance migration of pollen. To achieve this, the first Europe-wide pollen forecast had to be created. The current Norkko warning system, in turn, is based on this forecast. The chain of events serves as a useful reminder that the work of researchers can result in significant further applications that might not become finalised products until long after the research was started.

“The first thought shouldn’t be that something is impossible, but to ask if and how it could be made possible,” Siljamo says, summing up her long-term approach to research.

During her research stint in the UK, Pilvi and her family also earned merit at a colour obstacle rush. Photo from Siljamo family album

Original text in Finnish by Nina Mäki-Kihniä


Learn more about the Finnish Meteorological Institute, the workplace of Pilvi Siljamo, PhD, and about the SILAM atmospheric model. Pictured here is an inspection a pollen trap on the roof of the University of Worcester. Photo by Carsten Skjøth

Last modified 29 May 2018
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