Hi Kevin! You must be getting quite frustrated by now! This doesn't seem to be an easy one because there seem to be so many symptoms that don't coincide with each other!
There are only two bugs that fit the description you have given for roses. One is maybe a Fuller Rose Beetle, although they usually show other signs of being there before the bush just up and dies, like eaten leaves, etc.
The other is cockchafer and if you read it's life cycle, it sounds like it might fit. The cockchafer has a three year life cycle. After mating the female digs about 20cms into the soil to lay her 10 to 20 eggs. The eggs hatch after 21 days and the larvae remain in the soil for a further two years feeding on roots.
The cockchafer larvae are a creamy-white colour, with a brown head. They are equipped with a strong pair of pincers for chewing through roots.
If you pick one up it will make a squeaking sound by rubbing a row of pegs on its hind legs against its middle legs.
When they are about 5cms long they are ready to pupate in the soil. After pupation, the adult beetles emerge in October, and remain until the following spring.
The cockchafers are brown in color, slim, with four wings.
The other thing we haven't talked about is nematodes. These are tine worms that cannot be seen to the naked eye, but can also cause these symptoms. The clue to whether you have these is if there are small lumps, knots or galls on the roots. There are usually several of them. So you should check your roots for these.
Check these out and see what you think. We'll keep on the track, don't worry!
Val
