Combined impacts of pesticides and parasites on social bees: from the individual to colony level

Gemma Baron

Research output: ThesisDoctoral Thesis

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There is strong evidence for a decline in wild and managed bee populations. This is of concern both for conservation and agriculture, as bees play an important role in the pollination of wild plants and commercially grown crops. Agricultural intensification is likely to be one of several drivers of bee declines, in particular the habitat loss and increased use of agrochemicals with which it is associated. Bees in agricultural environments are therefore faced with a range of anthropogenic stressors such as pesticides in addition to the natural stressors to which they are normally exposed. This thesis explores the impacts of pesticides on life-history traits of social bees, and particularly in combination with additional stress from naturally occurring parasites.

The four research chapters explore impacts across a range of levels, from whole bumblebee colonies, to individual bumblebees, to the gut microbiota of honeybees. In Chapter 2, chronic exposure to a pyrethroid insecticide resulted in the production of smaller workers by Bombus terrestris colonies, but had limited effects on other aspects of colony development. In Chapter 3, colony founding B. terrestris queens, an essential yet vulnerable stage of the colony cycle, showed a reduction in colony initiation after exposure to a neonicotinoid. However, no interactive effects with the parasite Crithidia bombi were found. In Chapter 4, a reduction in feeding and oocyte development in multiple species of bumblebee queens was observed after exposure to a neonicotinoid. Finally, in Chapter 5 symbiotic lactic acid bacteria found in honeybee guts were exposed to a range of pesticides in-vitro. Both inhibition and promotion of bacterial growth occurred, although no consistent patterns were detected.

Overall, I found variable impacts of environmentally realistic doses of pesticides on lifehistory traits of bees. Some of these have important implications for conservation and agricultural policy and management.
Original languageEnglish
Awarding Institution
  • Royal Holloway, University of London
  • Brown, Mark J F, Supervisor
  • Raine, Nigel, Supervisor
Award date1 Jul 2015
Publication statusUnpublished - 2015

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