Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Mortality and depopulation in domesticated bee colonies: the American case.

Abstract

Domesticated bee populations have been in decline in North America for approximately 20 years, but in recent years significant losses have been attributed to "Colony Collapse Disorder" (CCD). A 2007 survey showed the presence of CCD in 35 states in the USA and in one Canadian province, with losses of 30-90% of bees in apiaries being recorded. Adequate control measures cannot be taken without knowing the causes of CCD. The US administration has provided substantial funding for the development of a national surveillance network and research into the causes of this syndrome. One factor that may contribute to CCD is the use of pesticides, which can have toxic effects on bees and weaken colonies. Chemicals used in fighting diseases in bees, such as acaricides used against Varroa destructor, have also been cited as possible causes of CCD. American researchers have analysed samples of bees from colonies that have been affected with CCD for the presence of parasitic mites such as Acarapis woodi and V. destructor, as well as pathogens such as Ascosphaera apis, Nosema apis and Nosema ceranae, but have found no clear links between the presence of these parasites or pathogens and the occurrence of CCD syndrome in colonies. Other possible causes of CCD that have been considered include a lack of good quality pollen, toxic effects of nectar gathered from transgenic crops, poor beekeeping practices, decreasing genetic diversity in the North American bee population, and the effects of intensive farming. Researchers at ten American laboratories combined their efforts in an attempt to identify all pathogens present in bees from CCD-affected colonies. Of the 19 pathogens identified, the presence of only one was clearly correlated with CCD, namely Israeli Acute Paralysis Virus (IAPV). However, it is unclear whether IAPV is a causative agent or merely a marker of the syndrome. Symptoms shown by CCD-affected bees are not the same as those observed in IAPV-affected bees in Israel. An interaction between IAPV and the varroa mite, which reduces the immune defences of bees, may be involved. It appears almost certain that the causes of CCD are multi-factorial, and involve a combination of pathogens, beekeeping practices and environmental factors.