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The Use of Sunflower Oil on Vigna Unguiculata Subspecies as a Pesticide with Callosobruchus Maculatus

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Introduction

The Callosobruchus maculatus (bean beetle) is a major economic burden to the societies in Africa and Asia due to the fact that these beetles are responsible for destroying farmers’ legume grains. The bean beetles have distinct appearances in relation to their genders. For example, the male beetles are smaller, brown, and have two back ligaments, while the female beetles are larger, black, and have one back ligament. The Callosobruchus maculatus live in conditions with low water supply and high temperatures. The Callosobruchus maculatus are an agricultural problem for the farmers because they lay their eggs on the legume plants burrowing their larvae into the pupate eventually killing these staple crops from the inside. This accumulates over time leading to a decrease in output for the farmers in these regions. In addition, according to E.A. Brown et al’s research, the two week lifespan of the Callosobruchus maculatus serves as a problem to the farmers, since the bean beetles spend most of their time mating and reproducing. This in turn leads to a bigger overall population of these agricultural nuisances.

The presence of Callosobruchus maculatus on the plants prevents the farmers from using pesticides to kill these beetles due to the fact that the pesticides inhibit the growth of the plants while at the same time only affecting some of the bean beetle larvae. According to the research done by Cruz et. al, the bean beetles are the biggest deterrent to the growth of cowpeas, which provide essential nutrients to humans and animals. Therefore, a safe alternative pesticide is necessary to protect these farmers’ crops.

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Specifically, sunflower and vegetable oils could inhibit the growth of Callosobruchus maculatus populations. Sunflower and vegetable oils are relatively inexpensive and easily obtainable for rural farmers. They have also been used previously to control other insect populations according to Boeke et al’s research. Sunflower oil reduces the adult life longevity of the bean beetles based on the research findings of Rajapakse. Additionally, based on Torres et al’s research, the bean beetles reproduce and bury their eggs inside the beans without the presence of food or other nutrients.

Based on the research previously mentioned, the hypothesis for this experiment is that sunflower oil can be used as a pesticide for the Callosobruchus maculatus. The sunflower oil will work effectively as a pesticide due to the fact that sunflower oil has already been used to control other insect populations in previous studies.

For the experimental design, the independent variable that will be used to test the hypothesis will be the concentration of oil ( 5 mL/1 kg or 20 mL/1 kg) placed in each bean environment. The dependent variable for the experiment will be the amount of eggs produced on the beans in each quadrant on the petri dish. The petri dish will be separated into four quadrants (A, B, C, and D). Quadrant A will have no sunflower oil, quadrant B will have a low concentration of sunflower oil (5 mL/1 kg), quadrant C will have no beans at all serving as the control, and quadrant D will have a high concentration of sunflower oil (20 mL/1 kg). The petri dish will contain five female beetles and five male beetles that will be introduced to the petri dish environment in quadrant C. The petri dish will be taped for the span of one week and the dish will be observed after one week. The overall assumption is that the environment with the most concentration of sunflower oil will lead to the least amount of eggs.

Materials and Methods

In this experiment, the main specimen observed was Callosobruchus maculatus (Bean Beetle culture, obtained from Carolina Biological Supply Company, item # 144180) and sunflower oil (Expeller Pressed Spectrum Organic Sunflower Oil, The Hain Celestial Group, INC.) to test the relationship between the number of eggs on each black-eyed bean (Vigna unguiculata) (First Street black-eyed peas Smart & Final brand) in order to see if sunflower oil is a an effective pesticide. In the experiment one petri dish was divided into four labeled quadrants (A, B, C, and D). In each labeled quadrant, there were different concentrations of sunflower oil on each bean to ensure that each of the beans had an equal amount of oil for its respective concentration. The three quadrants were labelled No Oil’, Low Concentration (5 mL/1 kg), and High Concentration (20 mL/1 kg). Ten regular black-eyed beans (were placed in quadrant A. In quadrant B, there were 10 black-eyed beans (covered with a low sunflower oil concentration (Expeller Pressed Spectrum Organic Sunflower Oil, The Hain Celestial Group, INC). In quadrant C, there were no beans. In quadrant D, there were 10 black-eyed beans covered with a high sunflower oil concentration. In the petri dish, 5 females and 5 males were placed in quadrant C. After placing the bean beetles in quadrant C, the petri dish was stacked and taped along the edges. The initials of each member of the lab group were then written on the back of the dish.

The controls of the experiment were the quantity of beetles that went into the petri dishes, the number of starting beans in each quadrant, and the different sunflower oil concentrations in each quadrant. The same population of beetles was used in the experiment to prevent any inconsistencies in the reproduction and mating process. The number of starting beans were also kept constant throughout the three dishes to prevent any inconsistencies in the number of beans would cause an increase in less egg production since the bean beetles use the beans as a place to lay their eggs: they burrow the eggs. Additionally, the different concentrations of sunflower oil in each quadrant was kept constant to provide a base for the experiment. If petri dish had different concentrations of sunflower oil, the data would be inaccurate. The plates were left at room temperature for approximately 7 days until the adult beetles died. After a week, the petri dish was cleared of all of the bean beetles. The dead bean beetles were disposed of properly and the eggs were collected in the culture. A stereo microscope was then used to examine each bean. No eggs were found burrowed in the beans.

Based on the findings of other groups, the bean beetles had no immediate reaction to the presence of sunflower oil. Our group concluded that the bean beetles migrated freely around the plates. In addition, there were significantly less eggs found on the beans with higher oil concentration (20 mL/1 kg) than the beans that had low concentration (5 mL/1 kg) and no oil (0 mL/1 kg). However, this did not apply to groups 2, 3, and 7. Groups 1, 6, and 7 demonstrated the trend that there was a higher mean number of eggs in quadrant A (no oil) of all three petri dishes, quadrant B with had the second highest mean number of eggs, quadrant D with the high concentration of sunflower oil had the third highest mean number of eggs, and lastly quadrant C had no eggs, since it served as the negative control. From the data, our group concluded that there is a negative correlation between the amount of concentration of sunflower oil on the beans and the number of eggs on the beans, disregarding quadrant C. After the experiment, our group discovered that sunflower oil is a pretty effective pesticide due to the fact that the environment with the high concentration produced fewer eggs than quadrants A and B.

Discussion

Based on the results that our class collected, our hypothesis was supported due to the fact that the natural sunflower oil served as an effective pesticide for the Callosobruchus maculatus for certain groups. The data from some of the other groups indicates a high standard deviation and average of eggs per bean on the higher concentration of oil saturated beans. This demonstrates that there was a major error in the experiment for these groups. The sunflower oil should have produced a low standard deviation and low number of egg production for quadrant; however, the exact opposite occurred indicating that the groups most likely did not put a sufficient amount of sunflower oil in quadrant D. In addition, two groups did not find any eggs on the beans for quadrants A and B, thereby shifting the averages and standard deviations for each quadrant. According to the research done by Fox et al, the sunflower oil should have suffocated the bean beetles. The oil gets rid of the insect eggs and larvae by penetrating the shells and stopping their metabolic and respiratory processes. Similarly, many other pesticides interfere with their biochemical processes killing them instantly. These biochemical processes are also present in humans and other animals affecting the which is why they can affect the crop yield for health of crop consumers and the surrounding ecosystem.

Ultimately, the sunflower oil should have lead to decreased averages in the number of beans for quadrant D and B due to the fact that sunflower oil works as a powerful pesticide. A source of error could have resulted in putting the same-sex beetles in the same environment. This would have led to a higher standard deviation for the mean number of eggs, since there would be less, different-sex beetles mating and reproducing in the petri dish. This would in turn lead to a lesser amount of eggs. Additionally, there may have been error in the experiment when the other groups picked up the bean beetles. Other groups might have potentially injured the bean beetles leading to a lack of beetles.

Lastly, the male and female bean beetles could have segregated themselves from each other inside the petri dish leading to a decrease reproduction and egg production. The major limitation for the study was the short lifespan of the bean beetles and the amount of bean beetles in the petri dish. If more time could have been alloted for this experiment and more bean beetles could have been provided, the experiment could have been more accurate. Additionally, more samples of sunflower oil could have lead to better results for the experiment.

Future experimentation could include using unrefined oils as pesticides against insects. Unrefined oils are oils that have not been processed by large amounts of heat, and bleached or deodorized after extraction, whereas refined oils include oils that have been bleached or deodorized. In this situation, sunflower oil and vegetable oil are both refined oils. Future experiments could compare the effects of the refined and unrefined oils. Additionally, three different petri dishes could be included in the experiment instead of just one. This type of experimentation would positively affect society because it would provide farmers with new sources of pesticides that could protect their crops and foster more crop output. By decreasing the populations of insects, such as Callosobruchus maculatus, the production of cowpeas will increase drastically benefitting the economies of Africa and Asia.

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