Subject: can environmental variables induce visible mutations in fruit flies

I am designing a science fair project.My hypothesis is: If wild fruit flies are 
exposed to significantly altered environments (reduced or increased temp., 
greater and lesser amounts of light, lower and higher acidity in diet)then the 
fruit flies will produce greater numbers of mutant offspring.  I have a $300 
microscope. Will I be able to see the mutations if they occur or will they be 
more subtle?  Are there some better variables I could use?  Thank you very much 

Re: can environmental variables induce visible mutations in fruit flies