A new study draws on weather data to reveal how crop pests make the most of convection currents and promises to provide farmers with better predictions of crop attacks.
Surplus and freely available atmospheric data from weather-tracking ground stations in the US have enabled scientists to unlock a classic mystery of insect flight that will provide farmers with more notice of pest strikes to enable them to protect crops more efficiently.
The work, published online by Nature in Scientific Reports, comes from a joint team of scientists from Rothamsted Research and the University of Greenwich. It shows how insects rise in updrafts but at a slower speed than the surrounding air, and slower still as air speed increases, and fall freely in downdrafts, often faster than the surrounding air.
“Small migratory insects are lazy hitchhikers, using updrafts to fly upwards when the going is easy but barely resisting downdrafts when the going gets tough,” says Charlotte Wainwright, co-author and meteorologist at Rothamsted. “These findings will help scientists to predict when and where these pests will strike next.”
The team, for the first time with such a large dataset, tracked the vertical movement of insects in convection currents using data from high-resolution cloud radar to pick them out and from the pencil-sharp laser beam of Doppler lidar to plot their speed.
“These instruments are built, operated, and maintained for meteorological applications, and insect observations are generally considered a worthless by-product,” says Phil Stepanian, co-author and meteorologist at Rothamsted. “While useless to some, these measurements are pure gold for entomological studies, which have revealed the flight behaviour of millions of insects as they navigate a churning atmosphere.”
For past research, much of it at Rothamsted, scientists relied on nets tethered to barrage balloons to gauge insect densities and predicted dispersal with weather models that simulated aerosol movement.
The latest research shows how insects travel differently to aersols, and so disperse differently, which emerging mathematical models, based on observations from field trials at Rothamsted in the 1940s, have confirmed independently.
“It was immensely pleasing to see that the idiosyncratic behaviours of minute insects flying hundreds of metres above our heads in turbulent airstreams were predicted accurately by a mathematical theory that was crafted on a whiteboard months before the observations were processed,” says Andy Reynolds, co-author and theoretical physicist at Rothamsted.
A further achievement of the research is the way that it links observed density profiles of insects in the atmosphere to insect behaviours, a linking of patterns and processes that is a key objective of movement ecology.
