Explain how availability of food leads to variation in beetle population ? Is it inherited or not ? Why?

Explanation

When the beetle population expands by sexual reproduction, the bushes start suffering from a plant disease. The amount of leaf material that can serve as food for the beetles is reduced. As a result, the beetles are poorly nourished. The average weight of adult beetles decreases from what is used to be when leaves were plentiful.

The body weight decreases in such conditions. Such variations are not inherited traits.
Decrease in the body weight due to starvation is an acquired trait in beetles during their life time. It will not bring any change in the DNA, thus, this trait cannot be inherited.
After some time period beetle generations also decline resulting into elimination of the plant disease. Later, more leaves of bushes become available as food for the beetles, making them gain weight. The subsequent generations can then become more bulky.