Introduction
Native to many third world countries, specifically concentrated in Africa and Asia, grain legumes, specifically black-eyed peas (Vigna unguiculata) are a large source of protein and oil. As a very valuable food, they yield high value nutrients that are critical to the third world nations’ welfares (Fery, 2002). The presence of pests in these environments is detrimental to not only the health but also the economy of these communities depending on organic black-eyed peas because these peas are extensively grown and sold as a central crop.
The Callosobruchus maculatus, also called by its common preferred names Cowpea Weevil and Bean Beetle, is a widespread, dominant species of the beetles with an African origin. The Bean Beetle is a major agricultural pest of host organisms that are suitable for the larval development of the beetle species. The Callosobruchus maculatus has a short lifespan of no more than 14 days and during this time, female beetles will mate and lay as many offsprings as possible up to 115 eggs. As they reproduce and fertilization occurs, the transparent eggs get glued to the surface of the host organism as shown in Figure 2. The Callosobruchus maculatus’ life cycle consists of rapid reproduction and larval development on widespread host plants, making the species a major global pest. The offsprings of the Callosobruchus maculatus develop on the surface of the beans. Once developed and pupated, the adult bean beetle emerges from the bean, infesting the bean and leaving a visible hole.
The Callosobruchus maculatus is easily manipulated and therefore can be frequently seen in the laboratory setting. In this specific experiment, the manipulation of the beetle is important and significant because it allows the testing of sunflower oil as a pesticide for this species under controlled settings and regulations. This species prospers in between the temperatures of 25° and 30° Celsius and do not need to feed. Alpha-amylase inhibitors are used to restrict the fertilization of the Callosobruchus maculatus larvae.
Many people have taken many attempts to alleviate the aftermath of the Callosobruchus maculatus’ developments. Many farmers and harvesters depended on insecticides to kill the pests. However, the ramifications of this was more detrimental than beneficial to the Vigna unguiculata population because it imposed more environmental hazards, causing not only seed and pod damage but also harming the bean beetles (Hamacher et al., 2002). As an alternative, oils are found to preserve the bean beetle population while also decreasing the rate of oviposition of matured Callosobruchus maculatus, which would also decrease the damage on the legume surfaces.
In this experiment, we will test sunflower oil as our Alpha-amylase inhibitors to see if it is a successful non-chemical alternative to an insect pesticide. Instead of killing the beetles, we are testing to see that it will rather protect the beans with a slippery surface so the eggs can not glue onto the surface. Mahshid Alibabaie and Mohammad Hasan Safaralizadeh (2015) tested the fumigant toxicity of nutmeg seed essential oil on Callosobruchus maculatus and found that M. fragrans can be used as a pest control.
To test the sunflower oil, 5 female beetles and 5 male beetles are placed in a petri dish that is separated into 4 quadrants, labeled A, B, C, and D. Each quadrant will have different concentration of sunflower oil: the control with no sunflower oil, low concentration (5mL/1kg), and high concentration (15mL/1kg). The petri dish will be kept at room temperature and left for a week for the beetles to mate. After a week, the dish will be revisited and the number of eggs on the beans of each quadrant will be compared and recorded to see if the sunflower oil could be a potential pest control.
After receiving the data collectively as a lab section, the numbers only partially supported our hypothesis. However, there was fragmented data from other groups that could potentially support the hypothesis.
The sunflower oil, as a successful repellent, would be beneficial to the harvest of the grain legumes, reviving the plant in its nations. If the sunflower oil demonstrates success as a pest control for the Callosobruchus maculatus and Vigna unguiculata, then it would be able to serve as an antidote to the epidemic and could be implemented as a inexpensive commercial product.
Materials and Methods
To test the hypothesis, four groups within the lab section completed the same procedure to get the highest possibility of reliable data. Originally, the procedure was set to use 15 beetles of each gender and to repeat the same steps on three different petri dishes. However, due to the lack of resources, the number of beetles and petri dishes were proportionally cut down to 5 beetles of each gender and 1 petri dish.
As shown in Figure 1, one petri dish divided into four sections and labeled A, B, C, and D. The petri dish held ten beans in each quadrant with quadrant B holding no beans as shown in Figure 1. The beans were from Signature Kitchens brand by Better Living Brands, LLC. Ten regular Vigna unguiculata were placed in Quadrant A with no oil. Ten black-eyed peas covered with low sunflower oil concentration (5mL/1kg) were placed in Quadrant B. No black-eyed peas were added to Quadrant C. Lastly, ten peas covered with high sunflower oil concentration (15mL/1kg) were placed in Quadrant D. The Expeller Pressed Spectrum Organic Sunflower Oil was obtained from The Hain Celestial Group, INC. Five female bean beetles and 5 male bean beetles obtained from Carolina Biological Supply Company, item # 144180, were pulled and placed into Quadrant C of the petri dish. The petri dish was taped together and kept at room temperature for a week.
The control of this experiment was Quadrant A that held the ten regular Vigna unguiculata with no oil because it served as a comparison to what the natural effects of the beetle would be if a repellent was not used. This control would demonstrate the comparisons and the differences in the number of oviposition on beans depending on the presence or absence of the sunflower oil each quadrant of the petri dish. Quadrant C quadrant served as a negative control that allowed the beetles acclimatize into this environment from their previous environment.
A stereomicroscope was used to count the number of eggs laid on each black-eyed pea. After counting each egg on each bean, it was recorded on a drawn diagram of the segmented petri dish to gather the numbers. The starting number of Callosobruchus maculatus and Vigna unguiculata was ten beetles and 30 beans. After recording the changes after the procedure, the standard deviation and group averages were calculated for the sake of test accuracy.
Results
Figure 1. The petri dish held ten Vigna unguiculata in each quadrant with quadrant B holding no beans.
Figure 2. The transparent Callosobruchus maculatus eggs get glued to the surface of the Vigna unguiculata
Table 1. Number of Callosobruchus maculatus eggs laid on Vigna unguiculata manipulated with different concentrations of Sunflower Oil.
Effect of Presence of Sunflower Oil at Different Concentrations on the number of Callosobruchus maculatus eggs laid on Vigna unguiculata
Observed from the overall data, there seems to be the largest number of eggs in Quadrant A over the span of all five lab groups. After one week, there was an average of 40 eggs in Quadrant A which was the quadrant with no oil on the beans. When observing the data of Quadrant B containing a low concentration oil at 5 mL/1kg, one can notice a drastic decrease in the number of pupation from the preceding quadrant. In the negative control, Quadrant C with no sunflower oil and no beans, there was no oviposition observed across all lab groups. Lastly, in Quadrant D with high concentration oil of 15mL/ 1kg, data was observed where the numbers were a lot closer to those of Quadrant B than Quadrant A. Each lab group individually observed similar data to one another. When referring back to Figure 3 however, the high number of 61 eggs in Quadrant A for Plate/Lab Group 1 stands as an outlier against all the other lab groups for that specific quadrant.
Discussion
Across all group’s populations, the average number of pupation was highest at Quadrant A with no Sunflower oil and decreased continuously for Quadrant B and Quadrant D, respectively as shown in both Table 1 and Figure 3. This data means that within the population of 10 beetles, 5 male and 5 female, the female beetles pupate on more beans with no oil than on the beans with low and high concentration. However, it is important to note that the results could be less reliable because the sample size is smaller due to the lack or resources. Similar to the concept of hardy weinberg equilibrium, if the population or sample size is small, it shows less variation more possibly due to a small population rather than the effect of the independent variable. Other experiments with larger sample sizes, however, show similar results of natural oils being effective repellents of pupation of the bean beetles.
Kéita et al. (2000) conducted an experiment on Callosobruchus maculatus using essential oils as is testing repellent and resulted with a similar conclusion that the natural oil worked as pest control. Alibabaie and Safaralizadeh (2015) also tested the same species with nutmeg oil and resulted with the oil working as a repellent once the species is exposed for 24 hours. Rhaman and Talukder (2006) experimented with a different procedure, directly immersing the beetles in the oil and also on the beans. The effects of this was that the mortality rate was higher with the oil immersed beetles.
The high standard deviations in Table 1 can show room for variation and error. A small sample size could be a possible explanation to a higher standard deviation. However, with the results of this lab across all five lab groups with additional support from previous experiments and practices, it is shown that a larger population or sample size will not drastically change the data to disprove the hypothesis.
The sunflower oil demonstrated success as a pest control for the Callosobruchus maculatus and Vigna unguiculata and could serve as a more affordable pest control product, solving the epidemic more in harvest and economically.
References
- Alibabaie, M., & Safaralizadeh, M. H. (2015). Fumigant Toxicity of Nutmeg Seed Essential Oil
- (Myristica fragrans Houtt.) (MF, Myristicaceae) on Cowpea Weevil, Callosobruchus maculatus F. (Coleoptera: Bruchidae). New Horizons in Insect Science: Towards Sustainable Pest Management.
- Fery, R. L. (2002). New Opportunities in Vigna. p. 424-428.
- Hamacher, L., Faroni, L., Guedes, R., & Queiróz, M. (2002). Persistence and activity towards
- Sitophilus zeamais (Coleoptera: Curculionidae) of pirimiphos-methyl sprayed at different temperatures on maize. Journal of Stored Products Research, 38(2), 167-175.
- Kéı̈ta, S. M., Vincent, C., Schmit, J., Ramaswamy, S., & Bélanger, A. (2000). Effect of various essential oils on Callosobruchus maculatus (F.) (Coleoptera: Bruchidae). Journal of Stored Products Research, 355-364.
- Rahman, A., & Talukder, F. A. (2006). Bioefficacy of some plant derivatives that protect grain against the pulse beetle, Callosobruchus maculatus. Journal of Insect Science, 6(3), 1-8.