Locomotor Behavior of Sarcophaga bullata in response to various light stimuli Introduction: The species Sarcophaga bullata (flesh fly) is from the Kingdom Animalia, Phylum Arthropoda and Class Insecta. Flesh flies live all over the world, generally in warm, moist climates. The flesh fly goes through the process of complete metamorphosis that consists of four stages: egg, larva (=maggot), pupa, to adult in about eight days. Through these different stages of metamorphosis the flesh fly is a parasite and a self-sustaining organism until it reaches full maturity. The job for the fly is then to disperse the species and reproduce. Flesh flies can be both pests and important aspects to human lives. They help in biological research and in criminal investigations but they also carry diseases that can harm humans.
The locomotor response is greatly dependent on inherited behavior also known as innate behavior. This means that the stimulus appears to trigger a fixed response that does not vary according to the previous experience of the organism, commonly found in invertebrates.
Two terms, taxis and kinesis can describe innate locomotor responses. Taxis is an automatic movement directly toward or away from a stimulus. Kinesis is random movement, caused by a stimulus but not necessarily oriented by it. The ability for a flesh fly to reproduce is greatly dependent on light and temperature. Flesh flies are dependent on light and temperature. They completely develop before the food supply is exhausted; the rate at which the flesh flies develop is one of the most important factors in determining both the survival and reproductive success of the flesh fly larvae. Warm, long days and lots of sunlight increases the rate at which larvae develop into pupae and most successively into adult flies. The female flesh fly deposits the living larvae into decaying flesh of dead animals or feces. This is the stage where they are specialized for feeding and growth.
These elements aid in the reproduction of flesh flies therefore; it is hypothesized that these insects will prefer an environment that is abundant in warmth and light to enable the flies to reproduce effectively. Another hypothesis on the reaction of flesh flies to the different wavelengths of light is that the flesh flies will prefer green light over the red and blue. The reason this was hypothesized was because green appears to be the darkest and warmest color and the color to absorb light the fastest which will allow it to become warmer in a smaller amount of time as opposed to red and blue.
Materials and Methods: The materials and methods used to perform the experiments to test the hypothesis are stated as follows. For the first experiment dealing exclusively with white light, a sample of ten larvae were used to run the experiment. The track was set up using a strip of cloth towel that we dampened with water in the bottom. Most of the lights in the lab room were turned off and an electric lamp was set at one end of the track at a distance so that it would provide precisely nine foot candles (fc) at the center using the digital light meter. Four two-minute time trials were run with the larva being collected at the edges of the track at both ends. The larva were started off in the middle and after two minutes, which ever light they went towards they soon fell off the track into cups at the drop-off point of the track at both ends where we could count the number of larva attracted to each color of light. The number of larva on both sides of the center line and the temperature (measured in Celsius) for all three sections of the track is the information recorded. After each trial the light is moved to the other side and placed again at nine foot candles to ensure that the larva are not just traveling because they learned the behavior.
For the second experiment the effect of different wavelengths of light on the larvae is being researched and it is patterned after the previous experiment. The track is set up again with a moist cloth towel on the top of the track with the two cups and lamps at both ends. The foot-candles were measured at nine for the middle and the temperature was measure at the sides and the middle of the track with a thermometer. The track and environment remain the same. The variables are the color films place over the lamps. For this experiment red, green and blue are being compared. The trials are run with the red vs. blue films three times through letting each trial go for at least two minutes. We then counted the number in each cup at the ends of each side of the track. The next test was the red vs. green conducting the same three trial and then with the green vs. blue.
Results: Results for both of the experiments were developed from the data collected through the trials. For the first experiment the class data shows 96.944% of the larva responding to the light side of the track and 3.056% responding to the dark side (table 5). The second experiment shows a 90%-10% ratio in green compared to red, blue and red have a 90%-10% ratio also which is similar but, blue and green have a 70%-30% ratio.
Discussion: The data collected through the first experiment allows for the first hypothesis to be accepted. The larva generally shows positive taxis reaction to the light in comparison to the absence of light. The second hypothesis however, provided evidence for being true because data shows green to be the color with the most larvae attracted to it. Although, this does disagree with other group's results this could be due to many different things. For example, only three trials were done, if more were done we might conform to the majority. The intensity of the green and blue light is the component that makes it most appealing to the larva because of the intensity. This adaptation that larva have is likely to help them survive in their natural environment due to the fact that they slow down in cold temperatures and if they do not develop into the pupa stage before their food supply runs out they are unable to reach full maturity.
Many aspects of these experiments were strictly controlled. In the light vs. dark experiment the intensity of light, the length of the track, and the elimination of any actions due to habit were all monitored. Although, a few aspects should have been controlled, for instance, the temperature of the room and other lights left on. These elements all could have affected the results, but would have been equalized though the class data and individual results. An example of this is an experiment being performed near the back of the room may not be accurate because the larva might have been attracted to the ceiling lights instead of the control light.
Some of the data in the light vs. dark experiments does not follow the consensus because it has been found that some larva could show innate biological variability. That is they could have different genetic or environmental qualities that affect their reactions to light. This is one of the reasons why it is important to run many separate trials in experiments. When only a few trials are run, the results may not be consistent and will not show random sampling of the behavior.
The natural environment of the flesh fly larva is in dead animals or feces. This type of environment provides many other stimuli for the larva. Moisture and temperature both affect the larva; the rate at which flesh fly larvae develop into adults is greatly influenced by light and temperature because it determines the survival and reproduction rate. The stimuli in the experiment differ slightly from the normal environment because of this; the larva could act abnormally. For instance, the larva are not exposed to such radical changes in light, the possibility of them not being accustomed to such extreme conditions like presence of predators could affect the outcome.
The larvae have adaptations that allow them to obtain food and survive in nature. The oral hooks are an example of these; they are able to full in vital supplements like food that enables them to survive. Another adaptation is their light receptors; these are sensors that the larvae use in order to detect light. These could possibly be found in an experiment that consists of covering the body of the larva leaving one section open and change the area covered until the flesh fly shows reaction to a light stimulus.
The experiments that compare light versus dark worked well for providing the data needed. The pair data differed slightly from the class data for a few different reasons. For instance, each group had different larvae and each experiment was held in a different part of the room. These slight changes could have an affect on the data even slightly. This experiment could have provided information that was more accurate if a few things were changed. For example, the running of more trials could have provided a better representation of the actions. Also, longer time trials to see if the reaction to light is a longer process.