Need some help with designing an experiment. In 2012, the U.S. experienced one o

Question

Need some help with designing an experiment.

In 2012, the U.S. experienced one of the hottest years on record (2016 was hotter). Drought engulfed >60% of the country. The drought stressed pine trees in the Southwest and many died from bark beetle infections. One pathogen that attacks bark beetles is the fungus, Beauveria bassiana.

You notice in the field that certain strains of the fungus appear to kill more bark beetles than other strains. As a way to understand the interaction between bark beetles and strains of Beauveria bassiana, you are interested in determining, do different isolates of Beauveria bassiana differ in their ability to kill bark beetles? You have cultured two different strains of Beauveria bassiana from dead bark beetles in the Sacramento Mountains and collected numerous other bark beetles from ponderosa pines.

Design an experiment to test your question – it is fine to use a graph or a table in addition to words to describe your design. Make sure you design an experiment and NOT an observational study. Your answer should include a discussion of how your experimental design addresses each of the four key elements of experimental design (12 pts). Feel free to use a separate page to explain your experimental design.

What is your null hypothesis for this experiment? (1 pt)

What are your independent and dependent variable(s)? (2 pts)

What is your experimental unit, which is the unit of independent replication? (2 pt)

What is your sample size (this should be a number)? (1 pt)

Of the choices we covered in class, what statistical test would be most appropriate for analyzing your data? (1 pt)

What is the single greatest advantage of taking an experimental approach, rather than an observational approach, to address your question? (1 pt)

Explanation / Answer

Hi,
Aim: To detemine whether different isolates of Beauveria bassiana differ in their ability to kill bark beetles.
Principle: The bark beetles are susceptible to the pathogen. There are two different isolates from the infected sample. These pathogens can be artificially inoculated onto the test species of bark beetles.

Procedure:
1. Collect the two strains of pathogen from Sacramento Mountains.
2. Collect atleast 10 -20 bark beetles from both sacramento mountains (control) and from ponderosa pines (Test)
3. Infect artificially to botht the samples with each strain independently.
4. Prepare another set where both the samples are infected with the two pathogenic strain simulataneously.
5. Keep the beetles in the chamber and observe them every 2 - 4 h.
6. record the reading after 24 - 48h.
7. Isolate the pathogen from the dead beetles and confirm that they are the same strains which you used earlier. [ Koch's principle]

Observations:
The pathogens if have braod host range will kill both control and test samples. If the kill is present only in simultaneously infected case, then both the strains of pathogen are needed for infectivity.

The proposed experiment should have a hypothesis before initiating. We shall call it as null hypothesis.
So our null hypothesis is that, the Beauveria bassiana from dead bark beetles in the Sacramento Mountains does not kill the bark beetles from ponderosa pines.
We need variables to start an experiment. So our variables are bark beetles from both the places mentioned. Beauveria bassiana isolates.
Experimental unit is the infection of Beauveria bassiana to bark beetles from ponderosa pines.[test sample]
Independent replication unit is the infection of Beauveria bassiana to bark beetles in the Sacramento Mountains [control]
We need large sample size in order to confirm the data. Atleast 10 - 20 samples we need to test.
One of the best statistical test to determine whether the infection is successfull or not is student's T-test.
The infection and subsequent kill can sometimes be a chance event. We need to confirm that the pathogen has broad host range and for this, statistically significant results are needed. Observational appraoch does not include statistical component and hence can be biased.

Related Questions

Navigate

• Browse (All)
• Browse N
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.