This protocol describes how to make a simple adult Drosophila behavior observation chamber, and how to take high-definition photographs/videos of the morphology or behavior of different types of fruit flies in the observation chamber through relatively simple and affordable methods.
Drosophila melanogaster is a very powerful model in biological research, but a bad model for photography or videography. This paper describes a simple but effective method to observe and document the behavior or morphology of flies. Flies were placed in a translucent observation chamber c.a. Ø15 x 5mm (no food inside) or Ø15 x 12 mm (with an 8 mm-high piece of food inside). After covering with an ultraviolet (UV)/clear filter with high light transmittance, the chamber was placed under a 5-50x zoom stereo microscope, and mini light-emitting diode (LED) video lights were placed on both sides of the microscope to illuminate the chamber to obtain uniform, soft, bright, and nearly shadow-free light. Then, a compact digital camera with 3-5x optical zoom, which can record 1080 P high-definition or higher resolution video (at a frame rate of ≥30 fps), was connected to the eyepiece of microscope through a bracket, and photographs or videos were taken through the eyepiece. By adjusting the zoom knob of the zoom stereo microscope, it was very easy to track the flies and take panoramic or detailed close-up images as needed, while the camera recorded everything under the microscope. Because the flies can stay at any position in the chamber, they can be observed and recorded from all directions. The photographs or videos taken are of good image quality. This method can be used both for scientific research and teaching.
Drosophila melanogaster is an outstanding model in biological research; however, it is a bad model for photography or videography, as it is too small for a camera or a camcorder and too large for a compound microscope1. Despite excellent research described in the literature, most studies have only provided blurred, unclear images, rather than clear and sharp photographs with clear detail that illustrate the fly behavior being described. Moreover, although fly behaviors have been extensively studied (e.g., courtship and fighting), most of these papers have used illustrations to explain their research to readers.
This paper describes a simple and economical approach. Using this method, not only the various behaviors of Drosophila can be observed, but also all the details that can be observed under a stereo zoom microscope can be recorded clearly and sharply. Of course, this method can also be used to record the morphology of flies, as when they enter a sleep or semi-sleep state, the stationary model allows the user to take a photograph or a stack of photographs with different focal planes to get an extended depth of field photo. These methods can be realized without complicated technology and expensive equipment or even superb manual skills.
The video component of this article shows videos of several typical behaviors of flies. The purpose of showing these videos is twofold: one is to let audiences know what can be captured and present the image quality obtained by using this method; the other is to let new students who are interested in Drosophila, but thus far have not had the opportunity to actually observe the behavior of flies understand the behavior of flies (such as courtship, fighting) through these clear videos rather than illustrations or blurred images.
Supplemental Video: Fruit Fly Behavior: Please click here to download this file.
1. Construction of the observing/documenting system
NOTE: The materials needed to construct the fly behavior observing/documenting system are shown in Figure 1, and the completed system is shown in Figure 2. The protocol to construct the system and how to use it are described below.
2. Protocols for observation and videography of fly behavior
Shoot through a UV filter for clear and sharp images
Perform a simple experiment to observe the difference between a UV filter and ordinary glass in the laboratory. Take a fly culture vial, remove the stopper, place it under a stereo dissecting microscope, and cover it (alternately) with a UV filter and a Petri dish lid. The photographs taken in these two cases are shown in Figure 5. The photograph taken through the UV filter is clear and sharp, very similar to the photograph taken when the culture vial is not covered. The quality of the photo taken through the glass of the Petri dish is very poor even when the focus is accurate. Ordinary glass (or acrylic sheet) is not coated, the highest transmittance is 92%14,15, and the clear/UV filter with multi-layer coating has a light transmittance of 98-99%.
Thus, the image shot through ordinary glass (or acrylic sheet) is not as clear as the image shot through the clear/UV filter. Another important defect of ordinary glass, such as the lid of a laboratory dish, is its uneven surface. It can be seen in Figure 5 that due to the unevenness of the glass surface, part of the photo is clear and part blurred. Therefore, clear/UV filters should be used instead of using ordinary glass or acrylic sheets to cover the FBOC. The UV filter used in this protocol (Figure 5) was cheap (~$10), unbranded, and its light transmittance unknown. In other words, even if it is a cheap UV filter, the image captured through it may be much clearer and sharper than that captured through ordinary glass.
Good quality without expensive equipment
Fly behavior was recorded with a JPEG-only camera with a considerably smaller sensor (1/2.3'). Video resolution is 1920 x 1080 pixels (at 30 frames per second, fps); the quality of the movie is satisfactory. A cheap UV filter was used to cover the FBOC, and the stereo zoom microscope was unbranded. The cost of the LED light (e.g., GODOX led-p120) was approximately $70 for two packs (see the Table of Materials). In other words, the equipment used was very economical; however, the video quality is good, clearly showing the panorama of some behaviors of flies, such as courtship and fighting, and the details of some behaviors, such as oviposition and excretion. In other words, even if it is a cheap UV filter, the image captured through it may be clearer and sharper than that captured through ordinary glass.
Figure 6 is a photograph taken from the video recording showing the details of each part of the fly's body. Obviously, the use of a camera and a stereo microscope with better image quality will yield videos or photographs with higher image quality. If the camera has a frame rate of ≥60 fps with good image quality, far more details can be captured in greater clarity in behavior with lots of action or movement. Another advantage of this system is that because the camera is connected to a zoom stereo microscope, it is very easy to shoot from panoramic to close-up shots using the zoom system.
All-round recording
Observation and videography are usually done from the top; however, as flies can stay on any part of the FBOC: the vertical FBOC wall, the inclined food surface, and even the UV filter (with the abdomen facing upwards), and their bodies are perpendicular to these surfaces, their behavior can be observed and documented from multiple viewing angles. For example, it can be clearly seen in Figure 7 that the female fly is constantly rubbing the ovipositor with her hind legs during the process of laying eggs. This detail of egg-laying behavior cannot be seen clearly from the side5.
Figure 1: Photographic equipment and other accessories used to construct fly behavior observing and documenting system. Abbreviation: LED = light-emitting diode. Please click here to view a larger version of this figure.
Figure 2: Drosophila behavior observation and recording system. Please click here to view a larger version of this figure.
Figure 3: Illustration of the size and shape of food. Please click here to view a larger version of this figure.
Figure 4: Illustration of the FBOC complex. Abbreviation: FBOC = fly behavior observation chamber. Please click here to view a larger version of this figure.
Figure 5: Comparison between the photographs taken through the UV filter, through the lid of the laboratory Petri dish, and taken directly without any cover. Please click here to view a larger version of this figure.
Figure 6: An image taken from the video recording. Please click here to view a larger version of this figure.
Figure 7: An unusual perspective to observe the egg-laying behavior of fruit flies. Please click here to view a larger version of this figure.
Light is at the very heart of photography and videography and is the decisive factor for obtaining high-quality images16. Here, two LED video lights with adjustable brightness and color temperature were used as illuminators, and a translucent material was selected to make the FBOC. The LED light panels on both sides provided enough brightness, and the translucent material softened and scattered light, eventually producing uniform, soft, and bright light to illuminate the flies in the FBOC, without producing unpleasant overexposed or underexposed areas. The ideal illumination can be achieved without sophisticated and expensive lighting equipment. Here, the UV/clear filter used had very high light transmittance and low reflection to cover the FBOC, and the light loss is very small. These measures ensured clear and sharp images.
We connected a digital camera to the eyepiece of the stereo zoom microscope through a bracket and took photographs or videos through the eyepiece. All images that could be observed under the microscope could be recorded. By rotating the focusing button and lifting the microscope, it was very easy to track the flies in the narrow space of the FBOC and to zoom in or out as needed to record local details or overall dynamics, which cannot be achieved by using a video recorder or camera for direct videography of the FBOC. At the same time, the camera can be selected according to the image quality requirements. In fact, a digital camera can be connected to any microscope with an eyepiece through a bracket. The corresponding author of this paper has successfully recorded experimental results in this way for many years.
The compact digital camera used to record the behavior of fruit flies must have 3-5x optical zoom (digital zoom should not be used for video recording). The telephoto end of these cameras (~100 mm focal length) is used to enlarge the image in the center of the field of view to the entire screen, so that the final image obtained is a pleasant image with no vignetting around it. If a camera has only a wide-angle fixed focus lens, or an optical zoom lens above 7x, there will be more or less unpleasant vignetting around the captured image. Neither digital single-lens reflex cameras nor camcorders are suitable for the method described in this article. The camera must be capable of recording video with a resolution of at least 1080 P at 30 fps. If the camera cannot be powered by continuous power, more spare batteries must be purchased for replacement at any time.
The flies can stand on a plane at any angle, their bodies are perpendicular to this surface. Even when sleeping, they can stand motionless on the vertical culture bottle wall. Therefore, when shooting from top to bottom, as long as we provide them with a plane at an appropriate angle, the behavior of the fruit fly can be observed and photographed in all directions, without the need to shoot its behavior from the side of an FBOC. This is the reason for the quadrangular food pyramid design.
However, in this system, the camera cannot focus and lock the flies and shoot automatically as they move across the frame. The experimenter must always use the focus and zoom functions of the stereo microscope to track the flies for shooting. It is for this reason that the diameter of the FBOC should be small, and the depth of the FBOC should be shallow, so that the experimenter can quickly track the moving fruit flies. Some behaviors may need to be recorded in the dark17,18. This article does not discuss those aspects of fly behavior.
The authors have nothing to disclose.
We thank Professor Li Xiangdong and photographer Mr. Cheng Jing for helpful discussions and suggestions. This work was supported by the Exploratory Project (20200101) of the Life Science Experimental Teaching Demonstration Center of China Agricultural University.
compact camera, Nikon P310 | Nikon | 3-5x optical zoom, cam record 1080 P HD video | |
ethylamine foam | 60 mm x 60 mm x 15 mm | ||
Food Blue No 1 | CAS 3844-45-9 | ||
mini LED lights and transformer | GODOX | LED-P120 | have 5000-5600 K color temperature |
small container (e.g. bottle cap) | about Ø 15 mm x 20 mm | ||
UV / Clear filter | high-quality UV/Clear filter with high transmittance, 30-40 mm | ||
zoom stereo microscope | 5-50x zoom |