Hello again

Haven't posted for a while - small toddler, big garden, too little time
scenario - but I'd appreciate your help once again.

Last year we had a fab crop of raspberries but they all had little grubs
inside them. I understand that this is the larvae of the raspberry beetle.
So I've looked up some sources to see how to prevent attack (organic if
possible) and Pippa Greenwood suggests spraying with Derris (is that a dust
or liquid) and that timing is critical - at the 'pink berry stage'. Does
that mean just when the berry is forming, or when it starts turning ripe
(which to my mind might be too late)? And as berries are forming all the
time, does this mean lots of doses?

It's so irritating - how do shops manage to have such lovely produce and yet
home grown and tended gives 'nasties'. This was one of the things that
always put me off my Gran's fruit when I was little. It was horrid to think
that you had to soak them or put them in an airtight container to get bugs
out - and how could you be sure they were all gone? And we just love
picking strawberries straight off the plant and eating them and would love
to do the same with the raspberries.

All advice welcome.

TIA
--Poppy