Step 1: Identify Blastophaga.
Blastophaga is a fig wasp.
It is associated with pollination in fig plants.
Step 2: Understand fig inflorescence.
Fig has a special type of inflorescence called syconus.
Inside the syconus, different types of flowers are present, including male flowers, female flowers and gall flowers.
Step 3: Egg-laying site.
Blastophaga lays its eggs in gall flowers.
The gall flowers provide a suitable place for the development of larvae.
Step 4: Final conclusion.
Therefore, Blastophaga lays its eggs
\[
\boxed{\text{in the gall flowers}}
\]