They account for this factor, and several others, in the study. There's an world wide decimation of insect populations, and it has received minor coverage relative to its likely significance to ecosystems.
what significant effects could there be on ecosystems by a decline in bugs? (I'm sure there are some, just curious)
Think of a food chain, bugs are near the bottom meaning they are a food source for many other creatures like birds, reptiles, small mammals, fish. Fewer bugs means less food for mice, that means fewer mice, leads to less food for snakes, leads to fewer snakes, leads to less food for birds of prey, leads to fewer birds of prey.
There are many chains like this where bugs are a vital source of food. If there were zero bugs then these chains would collapse. Also, bugs are needed to pollenate many fruit bearing plants.
Also, a huge portion of food production is dependent on bees and other pollinators.