|Larvae removed from the crown of a dying blueberry bush|
|Prionus feeding damage to the crown of a blueberry bush|
The only way to confirm the presence of these insects is to dig bushes and examine the roots and crown for damage or larvae. As pictured, the larvae are larger than most other grubs found in the root zone, are widest at the head end, with strong jaws, and with bodies that are elongated rather than the typical "C-shaped" grubs of other beetles.
Update, 2 February 2013
As Bill indicates, these larvae have only been observed on 'Duke' bushes. We aren't sure what this means, but we suspect that 'Duke' may be stressed in some way that predisposes it to infestation. It's also important to note that management action taken against larvae this size will likely be ineffective because they are so entrenched within plant tissue. If Prionus is a more wide spread issue than we currently believe, we will need to determine when adults are active and egg laying occurs, since this would likely be the most effective time to initiate management.