you might be able to purchase the correct water bourne fluid from the likes of 'safeguard chemicals'?
that way you know you have obtain the proper stuff,from ebay you might just be buying water??
normally if you have found it in 1 area of the attic then you probably have in other areas.
have you used a hammer to bang the rafters to see if any frass comes out?
if it does it might be a good idea to lay some white paper directly underneath the suspected area to see if any fresh frass appears.
iirc this is the time for the adults to sort migrating out of the timber,depending on type of worm.
make sure you use the correct ppe,and a decent fume mask,also before spraying make sure you sweep the whole of the roofing timbers down
then lift any insulation,then you can spray to your hearts content.
also advisable to turn off electrics apart from the cooker socket,
but we used to use a pump and hose/lance setup,you may well be using a garden sprayer?
bear in mind what above has been said though.it MAY be old flight holes,but for peace of mind only you can answer that.