LAUSR

BACKGROUND The safety of fungal insecticides to apiculture is publically concerned but remains poorly understood. This study seeks to evaluate whether, how and why wide-spectrum Beauveria bassiana insecticides are safe to honey bees in a novel assessment system. RESULTS Mesonotum dipping with a 108 conidia/ml suspension and body contact with conidial suspension in sucrose solution caused high mortalities of adult forager bees at 25°C optimal for conidial germination and hyphal invasion. Intriguingly, colony sizes in the hives contaminated by the forager bees contacting viable and inactivated conidia at two sites (1.2 km in distance) respectively showed similar increase percentages (31.7% versus 29.2%) during a 4-week summer period of exposure to environment. No sign of fungal infection was found within each of monitored colonies. Neither was fungal outgrowth observed on surfaces of bee cadavers cleaned from each hive at either site. Hourly counts of cleaned cadavers from videotapes presented no significant difference in colony-cleaning behavior between the two sites. During the period, in-hive temperatures at both sites were persistently stabilized at ~35°C, which abolished conidial germination and were far above out-hive temperature range. CONCLUSION It is colony heating that protects honey bee populations from a risk of forager bees' contact with formulated conidia applied for arthropod pest control. No role was detected for colony self-cleaning behavior in protecting the bee colonies from the risk. This article is protected by copyright. All rights reserved.