pollinating strawberries

I have a few strawberries in the greenhouse. Do I have to pollinate them manually? There are not many insects around, especially in the greenhouse.

Thanks, sunshine. I have been pollinating them with a small paintbrush, but wondered if I need to do it.
Some of the middles are starting to swell up into a yellow cone, but some flowers have a black middle when they open which does not swell. Have you ever come across this? There are normal flowers as well as the ones with black middles on the same plant.

Thanks, Mum.
How interesting.. I bought new plants which arrived a month or so ago and put them in the greenhouse, so they must have got frosted in there. The black centres do look rather odd, but the plants are flowering a little early. Actually it might be a good thing that they will not develop as it will weaken the plants to produce too much fruit first season. They are the ones that bear fruit all summer.