Used properly, neem oil can be very effective at repelling Japanese beetles and other insects that feed on foliage. Be sure to purchase the pure, cold-pressed product, as other extraction methods can significantly reduce the amount of the active ingredient (azadirachtin) in the end product. I use the product packaged by Dyna-Gro. It works better than any other neem oil containing product I've used.

Al

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I usually just pick them off by hand as they much prefer the flowers to the foliage and will often remain inside the flowers feeding and/or mating after the flowers rolls up at sundown. I just give them a squeeze until I feel that satisfying crunch of squashed beetles inside and I don't get my hands dirty. The bumblebees feed heavily on the pollen of the flowers so I don't spray or do anything to risk harming them.