Vine Weevil in the Kitchen
Many thanks for your e-mail to Harrod Horticultural.
With respect to your first question on Vine Weevils, adults feed on the leaves of a number of plants. Favoured plants I have found them to be on are Fuchsia, Cyclamen, Yew and Ivy. Primula is one that many people have mentioned to me they have found them on. If you haven't found any damage on your house plants or larvae in the pots, I would imagine the adults you've come across have wandered in from outside. You are right they don't fly, but will roam quite a distance in search of food and are attracted to light so often end up indoors.
Your second question about using gravel, well personally I find gravel works well if its of larger size and non-uniform. Pea gravel, gravel of similar size or smaller I have found to be a problem as it does compact together leaving less gaps for water to drain. The coir bale will also be great for helping with drainage as it prevents the soil from compacting. I've grown numerous vegetables in soil containing coir and never had a problem, so hopefully you shouldn't experience any either.
Many thanks for your questions,
Pest Control Expert