To find the ratio of plain blue bugs to the total number of bugs, we can first count the bugs based on the information provided:
- There are 10 plain insects (5 in the first row and 5 in the second row).
- There are 2 insects with a different shading.
Therefore, the total number of bugs is:
\[ \text{Total bugs} = \text{Plain insects} + \text{Shaded insects} = 10 + 2 = 12 \]
Now, to find the ratio of plain blue bugs (which are the 10 plain insects) to the total number of bugs:
\[ \text{Ratio} = \frac{\text{Number of plain bugs}}{\text{Total number of bugs}} = \frac{10}{12} \]
To simplify this fraction, we can divide both the numerator and denominator by their greatest common divisor, which is 2:
\[ \frac{10}{12} = \frac{5}{6} \]
Thus, the ratio of plain blue bugs to the total number of bugs is:
\[ \boxed{\frac{5}{6}} \]