In Rio Grande do Sul, around 400 million dead bees were found by beekeepers - with another 100 million deaths reported in four other Brazilian states in the last three months.
Vice President of Brazil's Rio Grande do Sul beekeeping association, Aldo Machado, told Bloomberg his colony was decimated in less than 48 hours.
"As soon as the healthy bees began clearing the dying bees out of the hives, they became contaminated. They started dying en masse," Machado said.
Pesticides containing chemicals such as neonicotinoids and fipronil, which are partially banned in Europe, were branded as the main cause of the deaths.
The EU enacted a partial ban on neonicotinoids last year due to their threat to bees, while Brazil controversially lifted any restriction on the pesticide.
According to the BBC, environmentalists opposing the pesticides branded them as 'poison packages'.
Last year, researchers believed heavy use of pesticides in the French countryside was also the cause of a massive decline in bird populations in the area.
Conservation Biologist Benoit Fontaine, who described the situation as 'catastrophic', said: "Our countryside is in the process of becoming a veritable desert."