Japanese beetles, once again

Japanese beetle. Photo credit: University of Wisconsin Cooperative Extension.

My first Japanese beetle sighting this year was June 12 — just a couple bugs. In less than 24 hours, I have seen about a dozen Japanese beetles in 4-5 visits to the grapevines. I have crushed nearly all of the bugs. However, I see somewhat more evidence of munching that I'd expect from just these few pests.

Last year at this blog, I announced my first JB sighting on June, in similar fashion — just a few bugs. The 2011 infestation was not as bad as 2010, and here's hoping that this year will confirm the trend. Still, it only takes a handful of hungry pests to chew through a few grape plants.

By the way, I'm using a fruit tree spray that has captan, malathion and carbaryl — highly recommended for JB's. However, it does not seem to be working.

Question: How much leaf damage can the vines sustain without harming the fruit? I'd prefer to monitor and crush rather than wrap the vines in garden netting at this stage of the season. Thoughts?