In response to a question from an Internet user:
Are nematodes the panacea for eliminating the beetle larvae that infest my garden and that of my neighbour? There is no panacea when it comes to wrestling. I know that on Reunion Island they use a mushroom called
Beauveria Bassiana , which infects the larva. The results look promising. The nematode that seems most effective against cockchafer larvae is
Heterorhabditis bacteriophora. It enters the larva and the bacteria it contains destroy the larva. But there are two constraints, the soil must be moist for 5 weeks and its temperature above 12°C. The
total soil cover continuously by straw 5-7 cm in place or between crops gives good results. This cover provides shelter for populations of ground-dwelling insects that feed on larvae and eggs. But larvae resembling those of the cockchafer are numerous. It can also be other beetles, which certainly does not detract from the harmfulness of the larvae. But that can modify your action on the adults. At home in the south-east (you do not say where you are from) it is the larvae of
cetonines which are many. But mulching and picking up adults on spring evenings keep the number at an acceptable level.Below, a
cetoine 
rose chafer
