A recent study of insecticide use on American crops found that these biocides have become more toxic to honeybees in the past few decades despite significantly lowered application rates.
American environmental ecologist Maggie Douglas and colleagues studied the specific effects of insecticides on honeybees from agricultural application 1997–2012. Separate estimates were made for contact-based toxic loads, such as when a bee is sprayed directly, and oral-based toxic loads, when a bee ingests the pollen or nectar of a plant that has recently been treated.
The poundage of insecticides applied decreased. Contact-based bee toxicity remained constant. But oral-based bee toxic load increased by a 9-fold average, albeit with great variability. “The most dramatic increases occurred in the Heartland (121-fold increase) and the Northern Great Plains (53-fold increase),” reported Douglas.
“The main contributor to the increase in oral toxic load was insecticide intensity: a 16-fold increase in oral potency far surpassed a 64% decline in application rate. This dramatic increase in oral-based toxic load is connected to a shift toward widespread use of neonicotinoid insecticides, which are unusually toxic to bees when they are ingested,” said Douglas.
References:
Margaret R. Douglas et al, “County-level analysis reveals a rapidly shifting landscape of insecticide hazard to honey bees (Apis mellifera) on US farmland,” Scientific Reports (21 January 2020).
“Insecticides are becoming more toxic to honey bees,” ScienceDaily (21 January 2020).
Ishi Nobu, “Buzz off,” (30 March 2013).