Recently published research is the first to demonstrate the sub-lethal effects of pesticide residue exposure on honey bees, which play a critical role in the production of one third of the food that human's consume.
Judy Wu, a former entomology graduate student at Washington State University and Ph.D. student at the University of Minnesota, found that low levels of pesticides build up in honey bee brood comb wax and cause serious consequences for developing worker bees and the adult worker bee lifespan. Brood comb is the breeding quarters of a hive and the place where food is stored.
Bees are economically critical because of their pollination services, so colony health is a high research priority. While honey is valuable, it doesn’t compare to the contribution bees make as pollinators.
Contributing to colony collapse?
Wu surmises that the pesticide residue contamination in the brood comb and its effects may be a potential contributing factor to losses associated with colony collapse disorder (CCD). The term was coined in 2007 to describe the mysterious phenomenon that results in the disappearance of worker bees from hives. In recent years, the number of hives that beekeepers think should be healthy, but are not, has increased significantly.
Professor Steve Sheppard, chair of the Department of Entomology at WSU and a widely respected authority on bees, said CCD has many possible causes. However, he is confident that while sub-lethal pesticide effects alone do not explain the disorder, Wu’s research shows that low levels of pesticide accumulation cause abnormal honey bee development.
So is honey safe to eat?
The problems seen in honey bee brood combs are unlikely to occur with honey storage combs, so the honey people eat is unlikely to become contaminated. This is because:
1) honey combs are only used for the brief period during the year when bees are making honey from blooming plants;
2) the pesticides are generally highly lipid soluble, meaning they easily migrate into wax, but are poorly soluble in aqueous solutions such as honey; and
3) honey combs are not used to rear broods.
The pesticides involved in Wu's study include those used by beekeepers, growers and homeowners. They include miticides, insecticides, fungicides and herbicides. The accumulation occurs because beekeepers reuse combs to save on the expense of replacement.
Effects on development cascade through hive
Some of the consequences to honey bees that Wu found were delayed larval development and a shortened adult lifespan, which can result indirectly in premature shifts in hive roles and foraging activity.
Shortened bee lifespans dramatically change the dynamic of a hive. According to Sheppard, foragers are the bees that provide pollination and bring food back to a hive.
“A bee’s life span as a forager is on average only the last eight days of its life,” he said. “This research shows that, if raised with pesticide residues in the brood comb, an individual’s foraging life span is shortened by four days, a 50 percent cut.”
If there are not sufficient foragers, the colony makes up the deficit by using younger bees that are not physiologically ready. The result is a negative cascade through the hive all the way down to the larval bees because individual nurse bees must prematurely move toward foraging behavior and stop feeding larvae, Sheppard said.
In addition, according to Wu’s study, longer development time for bees may provide a reproductive advantage for Varroa destructor mites. Varroa mites are parasites that live in hives and prey on honey bees. The extended bee developmental period enables these mites to produce more offspring that devastate hives.