Bean Beetle Lab Report - lab PDF

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Morgan Rice, Madison Miluk, Kimberly Wadsworth, Emily Kemen BIOL1081L Section 014

Tuesdays 5:30-8:20 11 September 2018

The effect of bean size on oviposition in bean beetles (callsobruchus maculatus)

Abstract Bean beetles are a pest that can cause farmers to lose a large majority of their crops. By conducting our study we can better understand what size beans are prefered by bean beetles, so farmers can modify production of whichever size they prefer. We simulated the bean beetles in a controlled environment to test which beans they prefer, We found that bean beetles prefer whole mung beans to half mung beans. This means that farmers should modify their beans in a way that stops bean beetles from laying eggs on their whole mung beans.

Introduction Pests are organisms that attack other organisms, only for their benefit. A great deal of pests attack crops, and use them as shelter, or food. Studying the oviposition of pests can enlighten farmers of what the pests look for in a crop. Additionally, this will help farmers to genetically modify their crops, based on what the pests are not interested in. Specifically, we will be looking at how the Callosobruchus maculatus is a pest to bean farmers. This species of beetle,

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also called the bean beetle, is native to Asia and Africa. Studies of the C. maculatus has increased dramatically within the past couple of decades, along with the many discoveries of pesticides, and genetically modified organisms. There has been a discovered pattern of the oviposition of the female C. maculatus. Females tend to lay their eggs on larger, uninhabited beans in order to increase the chances of their young’s survival (Fox and Messina 2017). Additionally, it is important to know what reasoning is behind the oviposition of the female C. maculatus, because it could lead to pest control techniques. One technique that females use to determine where they want to lay their eggs is competition. Competition plays a large role in the survival of several larvae in a bean. There is a limited amount of resources for shelter, and nutrition. Inside of smaller beans, there is more competition between two larva for space. Therefore, usually only one larva is able to mature into an adult per small bean (Mano and Toquenaga 2008). C. maculatus females lay their eggs on larger beans because they will provide more nutrients, protection, and they will decrease the amount of competition between other larvae. Our experiment consisted of whole mung beans, and half mung beans. There was a significant difference in the amount of eggs laid on each. The female C. maculatus laid most all of their eggs on the whole mung beans because they were larger. Based on the results from this experiment, we hypothesized that the female C. maculatus would lay more eggs on the whole mung beans, rather than the half mung beans. Our null hypothesis was that the size of the bean does not affect the amount of eggs that a female C. maculatus lays on bean. We predicted that if we placed whole and half mung beans in a medium sized petri dish, the females would chose to lay more of their eggs on the whole bean because they are bigger.

Methods For this study, the bean beetles used where from the University of Cincinnati’s research lab. While studying bean beetles it was observed how they lived their life out, “Bean beetles complete their life cycle entirely on dry beans. For most species, eggs are deposited on the surface of beans” (Dowling et al). To correctly analyze the data received there was 4 separate replicas of this experiment to receive the most accurate and desirable outcome. There was a total of 5 bean beetles used in each experiment, there was 2 males and 3 females. To find the most preferred bean type there was 30 whole mung beans, and 30 half mung beans placed into medium petri dishes to effectively use the space the petri provided. Then the petri dishes where

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set aside for exactly one week, to be observed and report back the results. When the week was up, the collection of how many eggs were laid on each bean was recorded, to determine which beans had been more preferred by the bean beetle. The size of the beans was chosen from whole to half sized - beans to distinguish which bean would have been more likely to have oviposition. The amount of eggs were dependent on which beans the female bean beetles decided to laid eggs. To control certain variables that would take place in this experiment was the type of bean was chosen based of its size, the number of genders were chosen based of the possibility that one or more beetle could not, or would not perform at the necessary means for this experiment. The size of the petri dishes, and the amount of beans were to insure the beatles were comfortable enough complete the experiment.

Results There was a significant difference between the amount of eggs laid on the whole mung beans rather than the half mung beans (t-value= 8.93752527, df = 23, p >.005). More female beetles prefered to lay their eggs on the whole mung beans, rather than the half mung beans (see Figure 1). Total amount of eggs laid on the whole mung beans (n=24) averaged 61.5 eggs per petri dish (s=6.60588231). In contrast, the total amount of eggs laid on the half mung beans (n=24) averaged 3.29166667 eggs per petri dish (s=0.70061869).

Discussion During our study of the effect of bean size on oviposition in female bean beetles we have failed to reject our hypothesis that female beetles prefer to lay their eggs on whole mung beans rather than half mung beans. C. maculatus has been a problem for bean farmers, because of our study we have found that the smaller the beans the less likely a bean beetle is to lay their eggs. Females oviposit on the largest unused eggs first (Mitchell 1975). Our purpose was to help bean farmers find a solution, that will prevent them from losing anymore mung beans to bean beetles. This information is vital for bean farmers, they now have a clear understanding of which beans attract the most beetles. With this information farmers can find a way to modify their beans in order to keep beetles off of them. Making the Mung beans smaller would be the most beneficial route for farmers, it would lessen the chance of c. maculatus ovipositing on their beans. We found that our results correlate heavily with those of other studies. Small beans held the least amount of eggs, this is due to competition between larvae, if there is more than one egg

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planted on a small bean only one would mature due to the limited amount of resources per small bean (Fox and Messina 2017). This correlated with our study because many females avoided small beans in general, and mostly oviposited only on the large beans. Due to the many studies of C. maculatus farmers now have a clear understanding of how bean beetles lay their eggs on beans. They can use this information in order to benefit and increase the production of vendible mung beans.

References Downey, M. H., Searle, R., Bellur, S., Geiger, A., Maitner, B. S., Ohm, J. R., . . . Miller, T. E. (2015, October 08). A comparative approach to testing hypotheses for the evolution of sex‐ biased dispersal in bean beetles. Retrieved from https://doi.org/10.1002/ece3.1753.

Fox, C. W., & Messina, F. J. (2018, January 04). Evolution of larval competitiveness and

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associated life‐ history traits in response to host shifts in a seed beetle. Retrieved from https://onlinelibrary.wiley.com/doi/full/10.1111/jeb.13222

Mano, H., & Toquenaga, Y. (2007, May 05). Wall-making behavior as a proximate mechanism to generate variation in larval competition in Callosobruchus maculatus (Coleoptera: Bruchidae). Retrieved from https://link.springer.com/article/10.1007/s10682-007-9167-7

Mitchell, R. (1975). The Evolution of Oviposition Tactics in the Bean Weevil, Callosobruchus maculatus (F.). Ecology, 56(3), 696-702. doi:10.2307/1935504

Figures

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Figure 1: Mean number of eggs laid on each petri dish, in both the whole and half mung beans. Error bars indicate standard error....