There has been a study looking at the economics of late-season feeding by flea beetles in canola.

The study was done at Agriculture and Agri-Food Canada in Saskatoon to determine how economical flea beetles are on canola in late summer and potentially develop an economic threshold. 

Their study concluded that: “Flea beetle feeding on canola in late-summer is rarely an economic concern.  Flea beetle feeding that occurs when seeds in lower pods of canola are at the green stage or beyond is unlikely to affect seed yields regardless of the infestation rate of flea beetles. Even when
seeds are translucent to green, numbers higher than 100 flea beetles per plant, and for some cultivars higher than 350 per plant, may be necessary to cause significant yield reductions”

(Soroka and Grenkow. Can. J. Plant Sci. 2012: 97- 107).