A doctoral student at Tel Aviv University has found that insects less than a millimeter in size are able to navigate upwind thanks to unique adaptations in their wings and flight mechanisms – a discovery that may improve their effectiveness as natural pesticides.
Guy Britzman, Zavit – Science and Environmental News Agency
The laws of physics are changing, and with them the familiar rules of flight. The breeding of tiny flying insects. Photo: Amir Sarig
Insects are the smallest flying animals on Earth. Some, less than a millimeter long, have taken miniaturization to the extreme. In a world this size, the laws of physics change, and with them the familiar rules of flight. Research presented In the 53th Annual Conference on Science and the Environment, presents evidence that even microscopic insects are capable of flying and even do so against the direction of the wind.
Doctoral student Amir Sarig, from the laboratory of Prof. Gal Ribak, Faculty of Zoology at Tel Aviv University, and a fellow interface program, studied the flight of some of the smallest insects, including parasitic wasps, aphids, cambiums, and thrips. The goal of his research was to understand how such small creatures manage to rise into the air at all, and, more importantly, whether they are able to control the direction of their flight, or whether they are simply carried and drifted by the wind.
To test this, an experimental system was set up in the laboratory that included a wind tunnel adapted for insect flight with an observation window. There, the movement of their wings and flight was recorded. What turned out to be quite surprising: "We saw that they tended to fly against the wind direction," even when the wind speed was higher than their own flight speed. "It's just not what we expected to see," says Sarig.
Comb-like wings
This ability to fly against the wind stems from a series of structural and locomotor adaptations that insects have developed during evolution. Among other things, instead of sealed wings, certain species of tiny insects have wings that are sealed only at the base with comb-like decorations on the edges. Other species have a network of thin, dense bristles that completely replace the sealed wings, thus reducing the mass of the wing and making it easier to flap, without losing the ability to move the air flow around the wing surface. This can be likened to flapping a comb – an easier action than flapping a sheet of sealed paper.
In addition, some insects use a flight mechanism called "clap-and-fling." In this mode, the wings are pressed together and then suddenly opened on the side facing the direction of movement, creating a sudden air current that contributes to lift. Another mechanism documented in observations is a circular motion of the wing, reminiscent of a rowing motion. "This movement, which seems to draw a crescent moon, becomes more pronounced the smaller the insects," explains Sarig. "They probably propel themselves."
Very small insects. Tobacco aphid. Photo: Amir Sarig
The Lord of the Rings
In addition to the physical challenges, insects also face severe sensory limitations. Unlike our "normal" eyes, which consist of a single lens, insects have compound eyes that are made up of a very large number of small units. The smaller the insect, the smaller its compound eyes become, and the number of units they contain decreases. This means that its range of vision is very limited. However, in a series of experiments, it was found that the tiny parasitic wasp (Eretmocerus mundus), which is about 0.7 mm in size, is able to detect visual targets, such as ultraviolet light, and move towards them.
Simulations using the experimental results showed that when the target is larger, the insects detect it from a greater distance. However, the rate of successful landings on it decreases. This is likely due to the fact that when the target area is increased, even distant insects detect it, but not all of them manage to overcome the wind in their flight towards it. However, the higher the aerial flight ability of the insect, and the longer its flight endurance, the greater the chance that it will be able to reach the target even when the wind may be an obstacle.
During the observations, another finding emerged, indicating deliberate behavior: the wasps increased their flight speed when flying against the wind, as if trying to compensate for the resistance of the air current. Even when the wind direction was different from the direction of the light source, a consistent preference was recorded for flying upwind. This behavior suggests a unique navigation mechanism.
The four tiny insects. Photos: Prof. Gal Ribak and Amir Sarig
Going against the wind
One hypothesis for the preference for flying against the wind is that the wind helps insects identify odors in their environment. If an insect is drifting with the wind, the odor molecules also move with it, so it samples fewer odor molecules. Conversely, flying against the wind allows it to be exposed to airborne information and orient itself accordingly.
From the study Additional interesting results emerged for the parasitic wasps. In the wind tunnel in the laboratory, the wasp was able to move forward against wind speeds of up to 0.32 meters per second. Above this speed, it was unable to move forward and drifted backward. Its airspeed was measured at an average of about 0.34 meters per second, a value considered low compared to the winds blowing outside the laboratory walls and that characterize open areas. When wind speed was measured in the insects' natural habitats, it became clear that it weakens the closer they get to the ground or into dense vegetation. This phenomenon, known as a boundary layer, allows the tiny insects to fly in an area where the wind is less noticeable, thus improving their ability to control air movement.
These findings may also have important implications for agriculture. Insects such as the parasitic wasp are now an integral part of biological pest control systems, especially in greenhouse crops. Understanding the flight and navigation patterns of these insects could help with their precise and effective release, and improve their effectiveness as natural pesticides. The study offers a new perspective on the dispersal of tiny insects in the field: they don't just float on the wind, but their flight is purposeful, energetic and efficient, even in conditions that require them to cope with strong winds. It turns out that even when you're so small that you can barely be seen, you can still take off, choose a direction and fly against the wind.
More of the topic in Hayadan:
