Evaluate the algebraic expression for the given values of the variables.
\[
-x^{2}-4 x y+4 y^{3} ; x=-2, y=-1
\]
When $x=-2$ and $y=-1,-x^{2}-4 x y+4 y^{3}$ is (Simplify your answer.)

Step 1 ：Given the algebraic expression \(-x^{2}-4 x y+4 y^{3}\) and the values of the variables x=-2 and y=-1.

Step 2 ：Substitute the given values of x and y into the expression. This gives us \(-(-2)^{2}-4(-2)(-1)+4(-1)^{3}\).

Step 3 ：According to the order of operations, first calculate the exponents. This gives us \(-4-4(-2)+4(-1)\).

Step 4 ：Next, perform the multiplication and addition operations. This gives us \(-4+8-4\).

Step 5 ：Finally, perform the addition and subtraction operations. This gives us -16.

Step 6 ：So, the simplified value of the expression \(-x^{2}-4 x y+4 y^{3}\) for x=-2 and y=-1 is \(\boxed{-16}\).