Although its in Toronto, I guess it still covers Ontario. Likely there aren't many other groups or resources for Ontario.

The Toronto Entomologists' Association (TEA) welcomes everyone who is interested in the insects of Ontario. We are an association of mostly amateur entomologists. Although our meetings are held in Toronto, we extend far beyond that in our field trips, our membership, and our seasonal summaries. Come to our meetings, join us on our field trips, purchase our publications, apply for the research grant, join us! The TEA is a registered charity and a non-profit educational and scientific organization formed to promote interest in insects, to encourage co-operation among amateur and professional entomologists, to educate and inform non-entomologists about insects, entomology and related fields, to aid in the preservation of insects and their habitats and to issue publications in support of these objectives.