Prof. Joe Cummins explains why bees are especially susceptible to pesticides
Colony Collapse Disorder (CCD), a growing scourge of honeybees has struck again this year. The United Sates Department of Agriculture (USDA) reported a 36 percent loss of colonies in managed hives over the winter, up 13.5 percent from the previous year . USDA has yet to identify a single pathogen responsible for the disease, and has finally begun to study the interaction between pesticides and viruses or varroa mites as possible causes .
CCD is characterised by the complete absence of adult bees in the colonies with little build-up of dead bees in or around the colonies, but capped brood and food stores of both honey and bee bread are present, and are not immediately robbed by other bees. Attacks by hive pests such as wax moth and small hive beetle, if any, are noticeably delayed.
In a colony undergoing collapse, the workforce is insufficient to maintain the brood, and seems to be made up mostly of young adult bees. The queen bee is present, but the cluster is reluctant to consume provided feed such as sugar syrup and protein supplement .
The Institute of Science in Society has reviewed the evidence on the impact of pesticides and the synergistic interaction between pesticides (including Bt biopesticides now widely incorporated into genetically modified (GM) crops) and pathogens such as the fungal parasites [4-6] (Requiem for the Honeybee, Mystery of Disappearing Honeybees, SiS 34; Parasitic Fungi and Pesticides Act Synergistically to Kill Honeybees? SiS 35). That evidence was the basis for question to the European parliament urging immediate bans on the pesticides such as the neonicotinoid insecticides as well as GM crops containing Bt biopesticides  (Emergency Motion on Protecting the Honeybee, SiS 35).
In 2008, the German government took the extraordinary step of banning neonicotinoid pesticides (see Emergency Pesticide Ban for Saving the Honeybee, SiS 39).
The honeybee genome has been sequenced, and while rich in genes for behaviour and learning relative to other insects, it is deficient in genes for immunity and the ability to detoxify toxic chemicals such as the pesticides . The genes families involved in insecticide resistance in other insects are completely lacking. These shortfalls contribute to the sensitivity of bees to insecticides . Bees have been found to have immune systems comparable to insects such as flies and mosquitoes, but with about one third less genes devoted to immunity than other insects. Insects immunity i nvolves inducible synthesis of anti-microbial peptides and constitutive melanisation-encapsulation response to pathogens The reduced immune flexibility of the honeybee may be compensated by social activity such as hive cleaning . When bees are challenged by a bacterial pathogen, genes in the head of the bee are differentially expressed, and show neuroimmune-behaviour interactions similar to those of vertebrates . A dysfunction in both its immune response and behaviour triggered by exposure to pesticides could easily result in CCD.
The genetics of honey bees is now actively investigated. The male honeybee has 24 chromosomes (linkage groups) and mapping of the numerous genes has been achieved. Males are nor mally haploid, but diploid males are observed at low frequency. Worker bees and queens are diploid. One queen bee provides over 2 000 eggs per day; unfertilized eggs become males while fertilized eggs become workers . Bee breeding has had some success, but complicated by the breeding habit of the queen, which copulates while flying to avoid inbreeding depression. The problem of inbreeding in honeybees has been studied for over fifty years, and before that, beekeepers have recognized the problem for centuries. The population genetics of inbreeding and homozygosis (too many genes existing as identical pairs) was worked out in 1950 by James Crow and William Roberts in . Heterosis (hybrid vigour) in the honeybee was described in 1955 by Gladstone Gale Jr. and John Gowe r . There has been no evidence that inbreeding contributed to CCD because the experienced beekeepers recognize the problem and overcome it by providing for out-breeding. However, it is clear that the toll of CCD may result in obligatory inbreeding due to shrinkage of the bee population, and that will accelerate the demise of the honeybee.
Organic farms are proving to be sanctuaries for the honeybee from the ravages of CCD. The honeybees are exquisite social animals perfectly adapted for pollination and honey making, but far too delicate to withstand the onslaught of systemic pesticides and GM crops. Regulators are slow to control the environmental insults to the honeybees and unprepared to act on the precautionary principle. Saving the honeybee may be among the most compelling reasons to shift comprehensively to organic agriculture  (Saving the Honeybee Through Organic Farming, SiS 38).
Article first published 11/06/08
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