What are the lethal and sub-lethal effects of neonicotinoid insecticides on bees?
Updated July 13, 2019
Neonicotinoids are the most widely used class of insecticides. They attack an insect’s central nervous system, causing paralysis and death. While most uses aren’t intended to kill bees, research shows that significant incidental harm can occur; even at sublethal exposure, neonicotinoids can damage a bee’s ability to communicate, smell, navigate and simply move its body. Here’s what we currently know about the impact of neonics on bees, based on a recent review of the scientific literature on this topic.
After reviewing the literature, the specific effects in a study were each grouped into one of nine different categories. As you can see above, Reproduction is the category of impact most commonly documented. However, this could simply be the result of the number of studies looking at that particular outcome. And Reproduction, like all the categories, covers a range of specific effects. The tables below provide a look at the specific effects within each category.
|bee immobility||IM||Moffat et al. 2016|
|breathing||IM||Hatjina et al. 2013|
|feeding||TH||Elston et al. 2013|
|hygienic behavior||IM||Tsvetkov et al. 2017; Wu-Smart & Spivak 2016|
|locomotor skills in queens||IM||Wu-Smart & Spivak 2016|
|motor function||CL, DN, IM||Williamson et al. 2014|
|pollination services||TH||Stanley et al. 2015b|
|proboscis extension||AC, TH||Alkassab & Kirchner 2016; D̩mares et al. 2016; Thany et al. 2015|
|swarming||CL&TH||Sandrock et al. 2014a|
|time grooming||TH||Williamson et al. 2014|
|worker movement||CL, IM, TH||Scholer & Krischik 2014|
|learning||TH||Stanley et al. 2015a|
|memory, long-term||CL, IM||Alkassab & Kirchner 2016; Williamson & Wright 2013|
|memory, short-term and mid-term||IM, TH||Stanley et al. 2015a; Williamson & Wright 2013|
|foraging activity||CL||Arce et al. 2016; Wu-Smart et al. 2016|
|flight duration (chronic exposure)||TH||Tosi et al. 2017|
|flight duration (acute exposure)||TH||Tosi et al. 2017|
|flight distance (chronic exposure)||TH||Tosi et al. 2017|
|flight distance (acute exposure)||TH||Tosi et al. 2017|
|flight velocity||TH||Tosi et al. 2017|
|forager recruitment||IM||Gill et al. 2012|
|foraging performance||IM||Cresswell 2011|
|foragers returning to patch||IM||Karahan et al. 2015|
|foraging trips||IM||Karahan et al. 2015|
|homing capacity||CL, IM, TH||Fischer et al. 2014; Yang et al. 2012|
|pollen load||IM||Gill et al. 2012; Stanley et al. 2016|
|pollen stores||IM||Wu-Smart & Spivak 2016|
|pollen trip (duration)||IM||Gill et al. 2012|
|pollen trip (successful)||IM||Gill et al. 2012|
|rate of return to colony||TH||Stanley et al. 2016|
|time spent foraging||TH||Stanley et al. 2016|
|workers lost during foraging||IM||Gill et al. 2012|
|daily mortality||IM||Abbo et al. 2017|
|life span||CL||Straub et al. 2016; Tsvetkov et al. 2017|
|mortality||IM||Alaux et al. 2010; Trayner et al. 2016|
|mortality (synergistic effects)||CL, TH||Sgolastra et al. 2016; Zhu et al. 2017|
|worker mortality||IM, TH||Mommaerts et al. 2010|
PARASITES, PATHOGENS, DISEASE
|parasites and pathogens (abundance)||various||Sanchez-Bayo et al. 2016|
|parasites and pathogens (spread)||various||Sanchez-Bayo et al. 2016|
|immune response||IM||Czerwinski & Sadd 2017|
|varroa infestation||CL&TH||Alburaki et al. 2015; Alburaki et al. 2018|
|body mass||IM||Abbo et al. 2017|
|depolarization in neurons||IM||Moffat et al. 2015|
|gene expression (variety of genes)||AC, CL, IM, TH||Christen et al. 2016; Simmons & Angelini 2017|
|hemocyte count||CL||Brandt et al. 2016; Hernandez-Lopez et al. 2017|
|neural stimulation||CL, IM||Moffat et al. 2016|
|neural sensitivity to substances||IM||Moffat et al. 2015|
|size of hypopharyngeal glands||IM||Alaux et al. 2010; Hatjina et al. 2013|
|thermoregulation||TH||Tosi et al. 2016|
|vitellogenin levels||IM||Abbo et al. 2017|
|wild bee density||CL||Rundlöf et al. 2015|
|olfactory associative behavior||IM||Yang et al. 2012|
This review is based predominately on two sources of information:
1. Supplementary materials from Mitchell and colleagues’ 2017 study, “A worldwide survey of neonicotinoids in honey”. Table S8 in those materials contains an extensive list of effects and references to the studies demonstrating each effect.
Mitchell, E. A. D., B. Mulhauser, M. Mulot, A. Mutabazi, G. Glauser, and A. Aebi. 2017. “A Worldwide Survey of Neonicotinoids in Honey.” Science, October, 109–11.
2. The IPI database which contains summaries of research articles on pesticides and their effects on invertebrates. The articles in the database have been reviewed and summarized by Xerces Society staff. This list was built from the results of a search for “neonicotinoids, bees”.
Effect: The impact descriptions were taken from the summaries of research in the supplemental materials and the IPI database. When necessary, I referred to the abstracts of the original research work for clarification. In listing the effects and grouping together different studies with similar effects, I was particularly careful not to combine effects that could be subtly but distinctly different (ex. decreases in “nest building” and “nest reproduction” are not necessarily the same thing); I preferred to risk duplicating effects on the list rather than miss an important distinction between them. In the interest of making the list easier to navigate and read, I grouped together effects into different categories that seemed to make sense.
Type of Change: The direction of each impact – “decrease” or “increase” – was also taken from the summaries of research in the supplemental materials and IPI database. When both “decrease” and “increase” are listed, it indicates mixed results within a single study or between studies. “Altered” is my own category for results that did not seem best represented by “decrease” or “increase” or both.
Type of Bees: The category “Honey bees” includes Apis mellifera. “Bumble bees” includes Bombus terrestris and Bombus impatiens. “Solitary bees” includes Osmia bicornis with a single occurrence of Osmia lignaria.
This project is on-going. If you have additional research that you believe should be included in the review, please get in touch with me [link to contact page].