Billions of insects join the “mile high club”

Entomologists have discovered that there are far more insects flying around above our heads than previously thought. Speaking at the Royal Entomological Society’s national meeting Entomology 2002, which will take place at Cardiff University on 12–13 September 2002, Dr Jason Chapman will say that in a typical summer month, around 3.5 billion insects fly over a square kilometre. This equates to one tonne of insects flying over Hyde Park in London, or Trelai Park in Cardiff, every four weeks in summer.

The discovery was made using a new Vertical-Looking Radar (VLR) monitoring system at Rothamsted Research. Using the VLR system, entomologists have also discovered that migrating insects can set their flight path to a particular compass direction, and that insects fly in discrete bands at different altitudes, much like the corridors used by commercial airliners. According to Dr Chapman of Rothamsted Research: “Data from the VLR show dense accumulations of insects occurring in discrete layers, often at altitudes as high as 800m.”

The VLR uses relatively inexpensive marine radar and microcomputer technology, and operates 24 hours a day. The radar transmits a narrow conical beam up into the sky, like a search light. The plane of linear polarisation in the beam is rotated, and the beam also wobbles by a very small degree about its central axis. These modifications allow the insect’s body alignment, and its position within the beam, to be accurately pinpointed. From the back-scattered signals, entomologists can work out the size and shape of insects (and thus often their identity) flying over the VLR, as well as their height and direction of flight.

“The VLR has many possible applications. Improving our understanding of insect migration could be important in tracking migrations of agricultural pests and their natural enemies. We may also be able to use the data to understand variations in breeding success of insect-eating birds and bats, and monitor the effects of global warming on insect populations,” Dr Chapman says.

Also speaking at Entomology 2002 will be Dr Richard Harrington, who will tell the meeting about a new pan-European aphid monitoring system known as EXAMINE (Exploitation of Aphid Monitoring IN Europe). The EU-funded project brings together, for the first time, aphid monitoring data from 19 countries. Because aphids are one of the most agriculturally important pests in Europe, the database will help entomologists to forecast aphid attacks and understand the impact of climate change on these insects.

According to Dr Harrington of Rothamsted Research: “Aphids are likely to respond more strongly than other insects to climate change because of their extraordinary reproductive prowess. Under current conditions, aphids can have 17 generations a year. With the 2°C warming expected this century, aphids would produce another five generations a year, and changes in pest status could strongly influence the viability of certain crops – and hence where we can grow them – in the future. Results from the UK show that after mild winters, many aphid species appear earlier, and in greater numbers at sensitive phases of crop growth. A 2°C warming can lead to aphids migrating a month earlier than normal.”

Dr Chapman and Dr Harrington will present their full findings at 10:40 on Thursday 12 September and 11:50 on Friday 13 September 2002, respectively.