The Effect of Macromolecules on the Movement of the American Cockroach, Periplaneta americana
by Nicole Steel
To determine macromolecule preference over short increments of time, we measured the movement of Periplaneta americana (American cockroaches). Cockroaches use their antennas to detect odors in their environment, which also serves as a tactile method to discriminate between food options. Cockroaches assess the benefits of food benefits through odor using the sensors on their antennas. Here, we provided cockroaches with several macromolecules (carbohydrates, lipids, proteins, and a mixture of the three) to assess their food attractiveness. We measured food attractiveness by what food the cockroach first approaches, regardless of consumption. The carbohydrate option (banana) attracted the most cockroaches when the food was placed at the edge of the choice chamber possibly because it provides immediate energy; however, when the food was placed at the center of the choice chamber, cockroaches most preferred the peanut butter.
KEY WORDS: Periplaneta Americana, macromolecules, short intervals
Insects interpret their environment using sensory receptors and have evolved physical adaptations (i.e. receptors on antennae, number or length of wings and legs) to meet their life needs. American cockroaches use the sensors on their antennas to detect odors in their physical environment and use this as a tactile method to discriminate foods that provide them with nutrients (Okada & Toh, 2001). Selection of food indicates that cockroaches will consider the benefits of the food and determine what is most beneficial to consume and to expend the energy for digestion. Once their antennas to detect chemical cues from their food, this signal is processed by the hypothalamus in their brain to produce a sense of hunger (Okada & Toh, 2001).
The nutritional demand changes over the cockroach lifespan. Food sources provide various ways to provide those requirements; for example, carbohydrates have been shown to accelerate the development of immature stages of German cockroach development while an adult female tends to consume high protein-level diets to increase reproductive rates (Mosayebian et al., 2017). Carbohydrates provide a fuel and fiber source for the organism as well as for the exoskeleton that protects the soft inner tissue of the cockroach (Srere et al., 2000). Lipids sustain long-term energy stores and compose the biological membranes of organisms (Srere et al., 2000). Proteins give structure to cells and release chemical signals (Srere et al., 2000). Understanding the nutritional (i.e., macromolecule) content of food will provide insight as to why the American cockroaches will prefer a specific type of food. We will analyze this preference over short-term trials to fill a niche in the scientific community which typically has tested over long-term trials such as in Lauprasert et al.’s experiment. While carbohydrates have the ability to turn into a form of sugar for quick energy, cockroaches face a more difficult challenge when digesting lipids. However, the relationship between environmental cues from macromolecules and the decisions made by the cockroaches require further investigation.
This experiment plans to investigate the relationship between food attractiveness of macromolecules and the rebuilding of a cockroach’s exoskeleton. Since amino acids compose new tissues and carbohydrates fuel this development, insects tend to consume foods with the appropriate balance of carbohydrates and proasZtein (Gall & Behmer, 2014). Identifying which macromolecule the cockroaches consume the most will provide insight into how injury could affect macromolecule preference.
The sex of the American cockroaches plays a role in food preference. Females generally require more protein for egg development while males do not require protein for fertility purposes (Lauprasert et al., 2006). To determine whether the sex of cockroaches affect food preference, we will compare the percentages of food that each sex is attracted to.
In this experiment, we will test determine macromolecule preference of American cockroaches by measuring food attractiveness (initial preference of the cockroach, defined as movement toward food), regardless of consumption. Previous work has investigated only long-term food preferences rather than immediate preference; therefore, we will use foods that represent combinations of macromolecules to examine what macromolecule is most important for the diet of cockroaches and how this is affected in short-term intervals. Cat food, olive oil, banana, and peanut butter represent protein, lipid, carbohydrate, and a mixture of all three macromolecules, respectively. We selected Dr. Tim’s All-Natural cat food to ensure high protein and low carbohydrate levels. We expect that there will be a relationship between movement of the cockroaches to the food of the highest energy, which will provide them with the greatest energy source. If given the choice of the three macromolecules and the combination of the three macromolecules, the American cockroach will choose the highest energy option, the banana.
To determine the food preference of the American cockroach, we evaluated the relationship between injuries and the sex of the cockroaches with their preference towards a specific food. We inferred a relationship between their food preferences and their movement. The significant effect of these two variables on food preference will be determined from the percentages calculated of food preference for each injury group and sex. A potential relationship of sex and injury on the significance of the food preference will be analyzed.
We tested fifteen American cockroaches, twice each, for a total of thirty trials. Cockroaches were placed in the center of four choice chambers that include a tablespoon of one of the following: peanut butter, olive oil, ground-up cat food, and banana. Olive oil represented lipids, cat food for the protein, banana for the carbohydrate, and the peanut butter as a mixture of all three of these macromolecules. We ground up the cat food with a mortar and pestle to ensure that the cockroaches detect the odor of the dry food. We tested two different conditions: food at the center or edge of the chamber. A closer proximity increased the odor of the foods and allowed the cockroach to detect all four types of foods easier. We collected data by examining food attractiveness. We based food attractiveness on which food the cockroach first detected by which chamber the cockroach first entered. However, if the cockroach consumes the food or if it travels to another chamber within thirty seconds, this information should be recorded.
Before the cockroach was tested, we examined its body condition to determine if the presence of physical injuries influences their food preference. We assessed damage to the cockroach’s antennas, wings, and six legs. These examinations of all fifteen cockroaches will be useful when assessing whether damaged or healthy cockroaches preferred similar foods depending upon the macromolecule necessary for their maximum functioning ability. Damaged cockroaches require more short-term energy than healthy cockroaches and therefore approach the banana (carbohydrate) at a higher frequency. The different levels of damage to the legs, antennas, and wings will be defined as the following: extreme damage is three detected injuries, major damage is two detected injuries, minor damage is one detected injury, and no damage is no detected injuries. The sex of cockroaches must also be examined. Males have styli on their rear next to their cerci while females do not have styli.
Controlling the experiment included using the same species of cockroaches and allowing all chambers to receive natural light. After each trial, we checked the amount of each food visually to ensure approximately one tablespoon of food remains in each choice chamber. Some aspects of the experiment proved to be uncontrollable. For example, the lab coordinator fed the cockroaches used in the second trial before the experiment. This led to more inconclusive trials, or that the cockroaches did not select a choice chamber. If the cockroaches consumed food before the experiment, their desire to consume food for any reason (i.e. long or short-term energy) would have decreased. Regardless of what food the cockroaches consumed before the experiment, we will not be able to evaluate the true macromolecule requirement of the cockroach. If the cockroaches consumed more of one macromolecule before the experiment, this would not have been measured and will provide an inaccurate reading for the actual experiment. Additionally, inconclusive results would mean a disinterest in any food, which means the previous food satisfied their appetite. This would not test the effect and benefits of macromolecules.
When food was placed at the edge of the choice chambers, the cockroaches preferred the banana the most followed by the peanut (Fig. 1). The cockroaches approached olive oil the least, and displayed a slight greater preference for cat food. When food was placed in the middle of the choice chambers (Fig. 2), there was more variability in cockroach preference than when food was located at the edge (Fig. 1).
During the second condition of food-centered cockroaches, the cockroaches preferred the peanut butter, followed by a preference for olive oil (Fig. 2). Banana, the first choice for the trials where we place food at the edge, fell to third preference. Cat food and inconclusive movements ranked lowest. In both trials, the cat food showed a small preference by the cockroaches. The cockroaches that we used for the second condition did have food in its terrarium before we conducted the experiment, unlike the cockroaches used for condition one, creating an unplanned limitation.
We analyzed the sex of the cockroaches used for the food-centered choice chambers. Males most preferred the peanut butter and least preferred the cat food. Females preferred the olive oil and cat food and disliked the banana and peanut butter. Using ANOVA two factor without replication, the sex of the cockroach does not affect the food preference; we identified no statistical difference between males and females since the p-value exceeds 0.05.
Table 1: The effect of damage on the food preference of American cockroaches. Extreme (3+ injuries), major (2 injuries), minor (1 injury), none (0 injuries).
Only the extremely damaged cockroaches did not select a choice chamber (inconclusive trials). The cockroaches with no damage detected traveled to the peanut butter and olive five times each, followed shortly by a preference of banana four times. Across all four levels of damage, cockroaches preferred the cat food the least. Using ANOVA two factor without replication, the health and condition of the cockroach based on injury does lead to a significant difference among the food preferences due to a p-value lower than 0.05.
To assess the food preference of American cockroaches over short-term time intervals, we evaluated the food attractiveness and movements of the cockroaches over thirty second periods. We also examined if injuries and sex of the cockroaches contribute to this preference. When food was placed at the edge of the choice chambers, we observed that most cockroaches preferred the banana over the other three food options according to food attractiveness. These results demonstrate the cockroaches preferred the banana with high levels of carbohydrates, possibly because it increased energy levels. Lausprasert et al.’s study examined the food preference of cockroaches over a 48-hour time period and presents data that shows consumption of all four macromolecules with varying levels of proportion. Males and females consumed the carbohydrates the most in this study. We observed similar trends in food attractiveness. For example, cockroaches preferred the banana (carbohydrate) the most and the cat food (protein) the least. However, when examining consumption of food in our study, the cockroaches ate only the banana in our short-term experiment. Therefore, it is possible that time duration does not affect the most consumed macromolecule.
When the center of the chamber contained the food, peanut butter, olive oil, and the banana became the most preferred foods (Fig. 2). During the second condition of the experiment, the cockroaches only consumed the banana. Since the cockroaches only ate banana, the odor of the peanut butter and olive oil could have overwhelmed the banana’s odor, so cockroaches were drawn to those choice chambers by the stronger scent rather than the benefit of the macromolecule. The benefit of the banana outweighed the benefit of the peanut butter and the olive oil due to the short-term gain of energy provided by the banana (Lausprasert et al., 2006).
In contrast to the first condition, in which the food was placed in the center of the choice chamber, we observed American cockroaches with no movement. When the food was placed at the edge of the choice chamber, the cockroaches selected a macromolecule in each trial.
During the first condition, we observed that male and female cockroaches consumed the protein the least because cat food offers a significant amount of protein. While female cockroaches need protein for egg development, too much protein lead to a rapid death while too little protein reduces reproductive rates as well as the size of their oothecas (Mosayebian et al., 2017). However, we observed no significant difference between the food attractiveness of males and females (Fig. 3). Although this experiment abided by shortened trials in comparison to the 48-hour trials of Lausprasert et al.’s study, we did not uncover a sex-linked preference for a particular food. This rejects our hypothesis that female would consume a higher amount of protein than the male cockroaches.
We observed a statistically significant relationship between injury and a type of macromolecule; however, using ANOVA, we determined that one of the injury categories had a statistical significance from the types of injured cockroaches. Therefore, the type of of injury does have implications towards the selection of macromolecules, but the extent of its significance requires further testing.
Only those designated with extreme damage fell into the inconclusive category with no movement (Fig. 4). Prior damage affected the mobility of the cockroach and its food preference in our experiment. For example, if a part of the cockroach’s body which has tactile hairs such as antennas or legs incurred an injury, the movement declines due to less receptors to detect sensory information (location of macromolecule), providing a slower overall reaction time for the cockroach (Tuthill & Wilson, 2016); therefore, we hypothesize that this is why only those with extreme damage fell into the no movement category (Table 2). This warrants more research on the effect of damage on the food preference of cockroaches.
Here we addressed the question of how limited periods of time affects food attractiveness, the effect of sex and injury on short-term trials, and how a mixture affects food preference of American cockroaches. This experiment suggests a trend between food preference and sex as well as food preference and injuries of cockroaches. This gives us a greater understanding of what variables affect the food preference of cockroaches. Additional research on the effect of specific nutritional needs over short-term intervals is needed. A long-term study should be performed for examining food attractiveness and food consumption, rather than just food consumption as done in Lauprasert et al.’s experiment.
Cockroaches create specific associations with macromolecules and their nutritional benefits through odor, which lead to their macromolecule preference over short-term intervals. Because the cockroaches only consumed the banana, this supports our hypothesis that the banana increased the energy level of the American cockroaches most when compared to peanut butter, olive oil, and cat food. This study fills a niche in the scientific literature community because it examines how sex and varying levels of damage affect the food preference of cockroaches; additionally, this experiment examines food preference over short intervals of time (two trials for a total of one minute per cockroach). Other studies examine food preference of the American cockroach over longer durations up to two days. Applications of this work include luring cockroaches with their greatest macromolecule preference into traps for extermination purposes. Since cockroaches are known for being pests, it is helpful to know what will be most desired by cockroaches in order to attract them. By incorporating macromolecules into a cockroach trap, we can lower cockroach populations in desired locations. Further research could evaluate food preferences with unique or novel traits.
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Acknowledgements: My Graduate Teaching Assistant, Margot Popecki, revised this countless times with me; her work is greatly appreciated.