Lund University

Lund University, founded in 1666, is home to a number of revolutionary discoveries. Ultrasound, dialysis and Bluetooth technology, to name just a few, were created here. Today the university remains one of Sweden’s strongest and broadest research environments. The Department of Biology alone comprises twenty-one research groups exploring a variety of areas, from protein production to ecological systems, and from genetic code to behavior. A specific area of research investigates flight control within complex environments. This research is led by Marie Dacke, Associate Professor, and Emily Baird, Assistant Professor, at Lund University. Their lab is part of the Vision Group.

Research on Flight Control

Set-up of the MotionBLITZ EoSens® Cube6 centred above a wind tunnel.

The purpose of their projects is to discover and describe how flying insects use visual information to control flight, avoid obstacles and to navigate safely through unpredictable environments. Their strategies not only reveal how a simple brain can extract and apply information from the visual scene to control flight, but they also suggest new, biologically-inspired ways as to how these tasks can be achieved in autonomous flying vehicles, across a broad range of natural environments, from bright open fields, to dark, cluttered rainforests.

Experiments on visual flight control are performed on a diverse array of insects, from bumblebees and butterflies to beetles and moths. A typical set-up of an experiment consists of an experimental wind tunnel and a high-speed camera mounted above it. The Dacke-Baird lab has two MotionBLITZ EoSens® mini1 and two MotionBLITZ EoSens® Cube6 high-speed cameras.

“The Mikrotron cameras are, in general, ideal for us because we can synchronize them,” says Emily Baird. “This enables us to reconstruct insect flight trajectories in three dimensions.” The trajectories are then used for computer modelling and simulation. The fields of research are numerous; this case study will introduce just four of them.

The aerodynamic function of the elytra

Flying beetle
During flight, the dung beetle (Heliocopris hamadryas) holds its elytra high above the wings.

One of the most important features of the beetle is its elytra. The elytra act as protective cases for the wings underneath and allow the beetle to exploit habitats that would otherwise cause damage to the wings and body. Many beetles fly with their elytra extended, suggesting that these influence aerodynamic performance.

To determine the aerodynamic function of the elytra, researchers in the Dacke-Baird lab explored the wake of beetles and compared it to the wakes of other flying animals. Six dung beetles (Heliocopris hamadryas) were tethered, thereby only allowing a pitching motion, and flown in a wind tunnel. Two synchronized MotionBLITZ EoSens® Cube6 high-speed cameras filmed the beetles while using lateral and top views to enable three-dimensional kinematics. The sample rate of 200 frames per second and wing beat frequency of about 40 Hz generated approximately five images per wing beat. Nineteen sequences of 100 frames were analysed. They show that while elytra support the beetle’s weight, they reduce its aerodynamic efficiency. You can view the research paper here

Ground speed control in bumblebees

Insects use optic flow to navigate through the world. Imagine a honeybee flying through a garden full of flowers. While passing the flowers, they appear to move backwards, creating a pattern of motion on the honeybee’s retina. This motion is known as optic flow. The flowers closer to the honeybee move faster than the flowers further away, similar to what we experience when driving a car. Distant objects like clouds and mountains move so slowly they don’t seem to be moving at all. Very close objects such as road signs move so fast they whiz right by you. Honeybees regulate their ground speed by keeping the optic flow speed constant. This means that they fly slowly when in dense vegetation and faster when entering an open field. Such a strategy ensures that their speed of flight is automatically adjusted to a level that is safe and appropriate to the environment.

The bumblebee needs 1,434 seconds, to fly from one region of interest to the next.
The bumblebee needs 1,434 seconds, to fly from one region of interest to the next.

While much scientific research has been performed on how honeybees use vision and optic flow for flight control, little is known about flight control in bumblebees. Do they apply the same strategy? How quickly do they detect and respond to changes in their environment? In order to explore these questions, the Dacke-Baird lab conducted a series of experiments. Bumblebees were trained to fly through an experimental tunnel consisting of parallel vertical walls. A MotionBLITZ EoSens® Cube6 high-speed camera was mounted above the centre of the tunnel, recording at a frame rate of 60 Hz.

The position of the bee and the orientation of the long axis of the body were determined using an automated tracking program. The results reveal that bumblebees detect and respond to environmental changes at a minimum viewing angle of 23 – 30 degrees, therefore reacting well before the new environment is entered. The research paper is available here

Visual flight control in naturalistic and artificial environments

When investigating visual flight control in insects, studies have usually been conducted under controlled indoor conditions. The insects would primarily see artificial stimuli such as computer-generated graphics shown on a display or two-dimensional images printed on paper. Studies, however, have shown that the neural response to moving visual stimuli varies, depending on whether the insects are presented with natural scenes or artificially generated patterns. Does this apply to the behavioural response as well?

Slow motion recording of flying bumblebees
To explore the effect of tunnel width on flight control, the bumblebees were recorded flying through a 30 cm wide tunnel (top) and a 15 cm wide tunnel (bottom). The frame rate was set at 120 fps.

To answer this question, researchers in the Dacke-Baird lab investigated how flight control in bumblebees is affected by whether the visual scene is two- or three-dimensional, naturalistic or artificial, or whether the experiment is conducted indoors or outdoors. The bees were individually marked and trained to visit a plastic sugar water feeder. This was placed at the end of an experimental tunnel, two metres in length. Indoor experiments were recorded using a MotionBLITZ EoSens® Cube6 mounted above the tunnel. Outdoor experiments were recorded using a Casio EXF1 video camera. Ground speed was calculated by digitising the position of the bee in each video frame and then finding the two-dimensional distance travelled between successive frames. The results suggest that visual flight control in bumblebees is not strongly affected by the differences between artificial and naturalistic environments. All the results are outlined in detail in the published article.

High-speed recording in rainforest

Infrared recording of a sweat bee on its way into an experimental tunnel.
Infrared recording of a sweat bee on its way into an experimental tunnel.

While working on this case study, Emily Baird went on a field trip to Panama. She took both MotionBLITZ EoSens® Cube6 cameras with her. Among other insects she recorded a sweat bee (Megalopta genalis) on its way into an experimental tunnel. This species flies exclusively at night, foraging shortly before sunrise and shortly after sunset. Their nests are found under thick canopy in the understory of Central and South American rainforests. The videos were therefore recorded in complete darkness while using infrared illumination. The MotionBLITZ EoSens® Cube6 was set at 50 frames per second and at the full resolution of 1,280 x 1,024 pixels.

“The cameras are easy to set up and easy to use – even in the middle of a rainforest at night,” Emily Baird points out. “They are extremely sensitive to light and we can film in the dark using infrared illumination from commercially available lights.” The EoSens® technology offers a photosensitivity of 2,500 ASA and was the reason why Emily Baird selected the MotionBLITZ EoSens® Cube6 over its competitors. Asked about the camera’s most important features, Emily Baird sums it up by saying: “They are light-sensitive, robust and easy to use.”