The headlines today are reporting massive bee kills in Dorchester County, South Carolina. On Sunday, August 28, 2016 the county sprayed the pesticide naled in an attempt to control mosquitos that vector the Zika Virus. Notification, which consisted of a post on a website, did not reach area beekeepers and did not give adequate warning. If a warning is received in time, beekeepers can reduce contact between bees and the pesticide spray by covering their hives and confining the bees to the inside the hive. Some beekeepers only learned about the spray after their bees were dead. One beekeeper who failed to receive the message reported the loss of 3 million bees in dozens of hives. Other area beekeepers have also reported bee mortality.
The pesticide naled has documented bee toxicity. Zhong and colleagues* studied the effect of naled sprays on honey bees and investigated ways of minimizing the effect on bees by controlling spray droplet size. They found that smaller ultra-low volume droplets deposited less residue, killed fewer bees provided more effective mosquito control. They noted that naled is more toxic to bees than malathion but much less toxic to bees than carbaryl or the supertoxic neonicotinoids.
Spraying only when bees are inside the hive will provide the greatest reduction in contact between bees and pesticide. At night, most bees are protected within the hive. In the South Carolina case, pesticides were sprayed after dawn, between 6:30 and 8:30 am. Planes must spray in daylight in order the see and avoid crashes. However, in the warm southern mornings, it is not unusual for bees to be actively foraging before 8:30 am.
Dorchester County is reviewing its notification system and updating it to provide direct alerts to local beekeepers. The most effective mosquito control relies on treating the larvae in their breeding sites. This requires advance preparation to survey sites and have a treatment plan. In general, aerial spraying is less effective, but used as and emergency measure when other mosquito control has failed. It is not clear that Zika is present in the South Carolina mosquito population and the sprays are a response to a document threat or if the threat is unknown and undocumented because the US government still is not fully funding Zika prevention in the US and its territories.
*HE ZHONG, MARK LATHAM, STEVE PAYNE, AND CATE BROCK. Minimizing the Impact of the Mosquito Adulticide Naled on Honey Bees, Apis mellifera (Hymenoptera: Apidae): Aerial Ultra-Low-Volume Application Using a High-Pressure Nozzle System. J. Econ. Entomol. 97(1): 1Ð7 (2004)