Simulator game in python
As mentioned in comments above, your question is about gamedesign. But since you brought your code here already, here's a suggestion: use better variable names - aa and b are very non-descriptive and as the amount of code will grow, you'll have a hard time to understand what's going on there with variables like these.
So instead of b, use something like MAX_POLLEN. When you'll see it in the code you'll immediately know what it is. And since it's UPPERCASE, which is a Python's convention for constants, you'll also know it won't change its value over time.