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1BraunBiology 1108 Research ArticleFrank Braun 19 March 2014

Mealworm Larvae Consumption Rate in Relation to Varying Environmental Temperature

Abstract:Digestion is an important function in all organisms, and with this in mind it seems logical that temperature should affect how much an organism is willing to consume. The purpose of our experiment was to determine at what temperature mealworm larvae would most effectively consume a food source. We chose to use mealworms as the subject in our experiment due to their constant drive to consume, so we created 4 different environments at (25, 30, 35, and 40 degrees Celsius) by heating water in a beaker on a hot plate. We then placed a petri dish filled with food and mealworms on the opening of the beaker. We let the mealworms eat within each set environment for 45 minutes, and after we compared the amount of food lost (in grams) in order to determine at what temperature they consumed the most comparably. We hypothesized that if mealworm larvae are placed in a moist environment with temperatures varying between 30.0C and 35.0C, these conditions should increase the rate at which they will consume, but we interpreted our data and concluded that as the environmental temperature increased, the amount consumed increased as well, proving that there is a direct relationship. Our experiment did not indicate an optimal temperature range, but instead exponential consumption as temperature increased. If there is a decrease in consumption, it exists outside of our tested parameters and could be tested with further experimentation.Introduction: Mealworms (Tenebrio molitor) play an important role in the care of many household pets and research specimens around the world today. They act as a large source of protein, and because of this they are bred and sold to pet stores, research facilities, and universities all over the world. Our group is interested in the area of mealworm digestion in relationship to temperature, but after digging for information we found most of the work done prior utilizes the mealworms as a food source for the subject instead of the actual topic research. Research has shown that there is a definitive relationship between environmental temperature and the rate of digestion/consumption, but we were not able to find any examples related to ectotherms (Krams 2014). Most of the work we found was done instead with endotherms, (which we are not dealing with), so we began to question whether the same was true in ectotherms. We then narrowed our focus to whether there is an optimal temperature/ temperature range where ectotherms consume the most, and we decided that mealworms would serve as the best test subject due their drive to consume in the larval stage.Mealworms are obviously ectothermic, and research has shown that when body temperature is raised, dietary processes and metabolic rate will increase as well (McConnanchie and Alexander, 2004). The ideal temperature range for mealworm egg development is from about 21.1C to 37.8C, and outside of these parameters mealworms cannot naturally hatch. It takes approximately 71 days for a mealworm to reach full maturity, and from the point they reach the larval stage their only goals are to eat and survive (Voris, Pfost and Woodbury, 1994). Even though our experiment is not related to the egg stage, it is important to understand at what temperatures mealworms live naturally. Because we know the temperature range that mealworm eggs hatch under, we can use that information to create realistic parameters for our experiment. This means that the data we accrue will be much me scientifically relevant and useful when viewed realistically. Temperature even plays an important role in the time frame of the life-stages, meaning that certain temperatures can hold back or speed up mealworm development due to internal factors receiving signals from external stimuli (or the external temperature). Tenebrio molitor undergoes complete metamorphosis (which means that there is no nymph stage, but instead develops from a larval to pupal stage).Mealworms also play an important role economically, which makes the understanding of how their consumption is impacted by temperature that much more valuable. As stated before, mealworms meet the needs of a high protein diet and are used to feed many specimens and pets. Mealworms are usually sorted and sold by size based on what size organism the consumer may have. So understanding how to manipulate size without the use of any hormonal stimuli would be an extremely valuable concept. Manipulating size via temperature instead of hormonally would be more cost effective as well as much more natural.Based on all of this information, we hypothesized that if mealworm larvae are placed in a moist environment with temperatures varying between 30.0C and 35.0C, these conditions should increase the rate at which they will consume (meaning anything above or below the stated range will diminish consumption).Methods and Design: We wished to determine an optimal temperature range for consumption in mealworms, so they best way we saw fit to test this was by creating four separate and testable groups of mealworm larvae. We chose 15 mealworms for each of the four groups from the population that we had been provided with for the experiment. We placed each group of 15 in a petri dish that was filled with an equal amount of food. We accurately weighed each group of food prior to placing it in the petri dish, and we recorded the weights so they could be compared with the final weights after the experiment was finished. We decided to use apples and potatoes as the food source in this experiment because they are not difficult to break down. Apples were used in trial 1, and potatoes were used in trial 2. We mashed up the apples and potatoes to ensure that the mealworms could spend the allotted time actually consuming and not just struggling to break off small pieces.The dependent variable for the experiment was the amount of food consumed by the mealworms, and our independent variable was the controlled temperature of the petri dish environment. Each petri dish environment differed by 5 degrees Celsius, and they were isolated to ensure that no extra heat was transferred. Group one was exposed to 30 degrees Celsius, group two was exposed to 35 degrees Celsius, group three was exposed to 40 degrees Celsius, and group four was exposed to 45 degrees Celsius. To conduct the experiment, we heated four 500mL beakers on hotplates with 200mL of water in each beaker. Once the beakers had reached the correct experimental temperature, we allowed them to stabilize and then placed each of the four petri dishes on top of the beakers. A thermometer was kept in each beaker throughout the course of the experiment to make sure that the temperature could be closely regulated and monitored. We let each dish sit for 5 minutes on top of the beakers without the mealworms. This allowed each environment to reach the proper temperature before actually beginning. Also by elevating each petri dish we were able to make sure that the mealworms were only exposed to the change in the air temperature inside the beaker instead of actually being exposed to the water. Once the 5 minutes was up, each group of 15 mealworms was placed in their heated environments and was allowed to eat for precisely 45 minutes. The mealworms were transferred as quickly as possible into each petri dish, and as soon as the larvae were properly moved the lid was closed and another group member immediately recorded the initial time. The mealworms were allowed to eat for a complete 45 minutes while each of our group members carefully monitored the temperature to make sure that the plates didnt throw off our set environments.After the 45 minutes had ended, each petri dish was removed, and all of the mealworms were quickly removed with tweezers to guarantee that the mealworms were not eating after the allotted time had elapsed. Once complete, we then weighed the remaining food on the same scale used prior (to keep consistent data) and subtracted the final weight from the initial weight. This calculated number represents the total amount of potato/apple eaten (in grams) by the 15 mealworms within the 45-minute period. We then compared the data taken from each of the four temperature groups and attempted to determine the relationship between increasing temperature and the rate of consumption in mealworms. Two trials of the experiment were conducted, and there were a couple changes made trials one and two. In trial one we took a water loss sample to reduce error caused by evaporation while the environments were heated. We knew that there would be no way to distinguish between the weight eaten by the mealworms and the water weight lost to simple evaporation due to heat. So in trial one, we sectioned off a portion of food inside the dish so mealworms couldnt access it and calculated the weight before and after to figure out what the water loss percentage was at that environmental temperature. We began our experiment using apples as our food source in trial one, but when we went to conduct trial two the following week there was only potatoes. So we went ahead and used potatoes as the food source in trial two.

The four groups being tested

A visual aid to help explain the setup described in the methodsThe four test groups and equipment from a different view

Results:

(Figure 1) Each temperature expressed on the graph represents each one of our environmental groups. The graph represents the amount of food that each of the 15 mealworms ate within the 45 minute testing period while under one of our four set environmental factors/temperatures.

Trial 1 displayed an increase in food consumed from .248 grams at the 30 degrees(C) environment to .661 grams in the 45 degrees(C) environment respectively; as the temperature increased there was a dramatic increase in the amount of food consumed by the mealworms (Figure 1).Trial 2 displayed the same trend as the amount of food consumed increased from .114g at the 30(C) environment to .168 grams at the 45(C) environment. As the temperature increased so did the amount of food eaten, but not at the dramatic rate seen in trial 1 (Figure 2 vs Figure 1).

(Figure 2) Each temperature expressed on the graph represents each one of our environmental groups. The graph represents the amount of food that each of the 15 mealworms ate within the 45 minute testing period while under one of our four set environmental factors/temperatures.

Trial 1 Data:(Table 1) represents the calculated weight differences of the food eaten in trial 1 by the mealworms before and after the 45-minute period. Temperature (C)Initial Weight of Food (g)Final Weight of Food (g)

303.0012.753

402.9972.688

403.0012.680

452.9932.332

Trial 2 Data Table:(Table 2) represents the calculated weight differences of the food eaten in trial 2 by the mealworms before and after the 45-minute period. Temperature (C)Initial Weight of Food (g)Final Weight of Food (g)

304.9204.806

355.0224.910

405.0224.875

455.0034.835

Trial Data Differences:(Table 3) represents the total data differences for trial 1 and trial 2.

Food Consumed (g) 30(C) Environment35 (C) Environment40 (C) Environment45 (C) Environment

Trial 1.248g-------------------.315g.661g

Trial 2.114g.112g.147g.168g

After viewing the data from the separate trials and the differences between the two overall, it is obvious that there is a much larger weight difference in trial 1 when compared to trial 2 (Tables 1 and 2). Both trials express that consumption increases while being influenced by increasing temperature, which leads us to believe that there is a direct relationship between consumption and environmental temperature. We were not able to identify a temperature (or a range of temperatures) that acted as an optimal level for mealworm consumption, but we instead saw an overall increase in consumption under increasing temperature.

Water Loss Data:

(Figure 3) represents the amount of water lost as the temperature in each in environment increased. The water loss calculations were conducted to analyze the amount of weight lost due to evaporation.

(Table 4) Represents the data used in the graph from Figure 3Isolated Food Before heating (g)Isolated food after Heating (g)Calculated Percentage (%)

.501.4725.8

.500.4568.8

.499.4588.3

.504.45110.5

In trial 1 we set up a test within our experiment to determine the amount of water lost simply due to heat. As the temperature increased, we saw an increasing percentage of our experimental mass becoming lost due to evaporation (Figure 3). The calculated percentages can be applied to our prior data by subtracting the percentage lost by evaporation to determine a rough value of reduced error (Figure 4 and Table 4).

Trial Averages: (With Water Loss Factors)

(Figure 4) This graph compares the average of the food consumption trials with and without water loss. The water loss series was calculated by using the water loss percentages to subtract from the original trials.

When the two trials are averaged as well as when the water loss is applied to one and not the other, it becomes obvious how large of a role evaporation played in this experiment. Though both lines maintain the same trend on the graph, one has considerably less mass than the other. This is seen as the calculated percentage of evaporation increased from 5.8% to 10.5% throughout the course of the temperature increase.Results Summarization:Our data indicated that there was a direct relationship between consumption in mealworms the temperature of their environment. We were not able to identify any ideal or optimal range, and we reject our hypothesis because there were no signs indicating that the 30-35C range was ideal. Our data expressed an exponential increase, and there was never a sign of decreasing consumption, so our data provides no evidence of any optimal range.

Discussion and Conclusion: After analyzing our data and viewing our graphic trend we came to the conclusion that as temperature increased, so did consumption (which implies a direct relationship), but we also realized that there was no evidence of an optimal temperature range within our experimental data. We hypothesized that the mealworms would consume the most in the 30-35 degrees Celsius range, but that was not the case. Our data displayed that as temperature increases, digestion increases directly, but we were not able to discover an optimal range. If our data had given evidence of an inverse quadratic shape it would have been easy to determine a range, but our data increased exponentially instead (Tables 1 and 2). Our original hypothesis was based off the concept behind how ectothermic organisms respond to temperature. We knew through our research that many ectothermic insects are stored at cold temperatures to cause a drop their metabolic processes, so we assumed the opposite would work in the case of our experiment (Krams 2014). Our maximum temperature was based around what the normal environmental temperatures are for mealworms, so we chose 45 (C). We figured that once the mealworms became too hot (hotter than their natural environment) their eating would decrease, and we could find the best environmental range. The 30-35(C) range was chosen in our hypothesis because that is around the temperature that mealworms naturally occur, so we hypothesized that their natural environmental state is where they would consume the most, but that was not the case in either of our trials (Figure 1 and Figure 2). Consumption never dropped off as the temperature went up, but it instead kept ascending to the end of our set parameters.There were some important sources of error within this experiment that negatively affected our data. In trial 1 we conducted a water loss test (Figure 3 and Table 4), but there were so many issues with maintaining the accuracy while conducting the test that we did not feel it was worth attempting in trial 2 (mainly because of the time constriction). Also in trial 1, we had issues maintaining the 35(C) environment. We had to average the data from two 40(C) environments instead because we could not keep the 35(C) stable enough to include it as viable data (Figure 1). One of our final sources of error was the fact that we had to switch from apples to potatoes between trials 1 and 2. There is much more water to be lost in apples, which could have put a serious toll on the accuracy of our data when we switched to the new food source. We also noticed that there are major weight differences between trials 1 and 2, but there are many unknown factors that could have influenced this (Table 3). The mealworms could have simply taken preference to the apples over the potatoes (which seems to be the most logical explanation) because even though our water loss test was not the most accurate, it does not seem plausible for that much water to have evaporated. Overall, swapping food sources was a serious issue in this experiment, but we had no choice due to our time constraints and the fact we did not have an apple available during the second trial. If we could conduct this experiment again with multiple trials and more time in the lab, we could utilize the information we learned from our data and set higher parameters to determine if the mealworms ever stop eating before they die from overheating. Most all of the mistakes were simple, and they could be quickly solved and corrected through another round of testing. We were not able to completely answer the question we were asking, but it can easily be found through further experimentation. After facing all of the issues we dealt with in this experiment, our group could apply what we have learned to do the experiment over properly and much more accurately. Answering these questions could have an important economic impact, and could reduce the use of unnecessary chemicals and hormones through the simple understanding of how heat impacts the consumption and growth of mealworms. Understanding how to manipulate organismal size at the time they are sold could be invaluable scientific knowledge, and through more testing and experimentation these answers may not be that far away.

References

Krams, I. (2014). High Repeatability of Anti-Predator Responses and Resting Metabolic Rate in a Beetle. Journal of Insect Behavior, 27(1), 57-66.

McConnachie, S., & Alexander, G. J. (2004). The effect of temperature on digestive and assimilation efficiency, gut passage time and appetite in an ambush foraging lizard, Cordylus melanotus melanotus. Journal of Comparative Physiology B, 174(2), 99-105.

Voris, J., Meyer, J.,Pfost, R., & Woodbury, R. (1994). Temperature affects lesser mealworm populations in turkey brooder houses. California Agriculture, 48(2), 18-21.