Reasoning for the toxicity?
In the question "Was the toxicity event due to a pesticide product? " the 50% of the people registering the event replied positively and they also accused specific crops.

International scientists formulate a roadmap as evidence that anthropogenic stressors are seriously reducing insect and other invertebrate abundance across the biosphere

Several neonicotinoid compounds are used in seed treatments of the most widely grown grain and oilseed crops worldwide. Most applications are made prophylactically and without prior knowledge of pest populations. A growing body of evidence suggests that these compounds become contaminants of soil, water, and plant products, including pollen and nectar.

Wild and domesticated bee species are exposed to a variety of pesticides which may drive pollinator decline. Due to wild bee sensitivity data shortage, it is unclear if the honey bee Apis mellifera is a suitable surrogate species in the current EU risk assessment scheme.

We defined the last observation timepoint at which increases in mortality were lower than 10% as a steady-state mortality level.