Ah yes, because insects have nothing to do with leaves... And glyphosate is the only chemical in it.

Wait, neither of those are actually true, are they?

Let's have a goo at the top three search results for "round up effect on insects"...

> "The chemical compound glyphosate, the world's most widely used herbicide, can weaken the immune systems of insects, suggests a study from researchers at the Johns Hopkins Bloomberg School of Public Health"

> "The active ingredient in Roundup, glyphosate, does not affect insects in the same way it impacts plants, but it does kill insects, either directly -- as in the case of a small number of honeybees in Monsanto's research -- or as a consequence of killing weeds."

> "Glyphosate—the most widely used herbicide globally—inhibits melanin production, which could have wide-ranging implications in the health of many organisms, including insects. ... Glyphosate also increased the burden of the malaria-causing parasite Plasmodium falciparum in A"

This doesn't seem like such an "unlikely" candidate to be playing a role to me.