This herbicide is said to have sub-lethal effects that fly under the radar of ecotoxicological studies
A study just published in Scientific Reports indicates that the glyphosate-based herbicide sold under the trade name Roundup does not adversely affect the survival of bumblebees. On the other hand, this product is said to substantially reduce male fertility, which could have repercussions on colony size and, ultimately, on the fertilization of plants that depend on this native pollinator.
The sub-lethal effects of pesticides are often overlooked in studies of the impacts of these products on organisms other than those they target, the study’s signatories point out. "We wanted to document one of these sub-lethal effects, namely the repercussions on the fertility of a pollinator native to Quebec, the febrile bumblebee, Bombus impatiens," explains research team member Pierre Giovenazzo, a professor in Laval University’s Biology Department.
In Quebec, the febrile bumblebee is an important pollinator of wild plants, as well as crop plants such as tomatoes, peppers, blueberries, cucumbers and cranberries. Its use in the pollination of these plants is recommended to ensure the production of quality fruit.
The scientists evaluated the effect of Roundup on 208 male bumblebees placed in crates in the laboratory. "In particular, we measured how exposure to this herbicide affected the number of live sperm produced by the bumblebees. The doses tested correspond to those found in fields after application of this product", explains Professor Giovenazzo.
The first surprising result was that the median survival of bumblebees exposed to Roundup was 28 days, compared with 23 days in a control group of 104 bumblebees. we don’t know what accounts for this increased longevity," admits the researcher. However, on day 10 of the experiment, males exposed to the herbicide had 34% fewer live sperm than those in the control group. The longer the exposure to herbicide, the fewer live sperm. Longer exposure could therefore have even more marked effects."
This drop in fertility can have substantial repercussions, especially for plants that depend on this species for pollination, explains Prof. Giovenazzo. "In the febrile bumblebee, the queen only mates once in her life. If mating takes place with a male that has few live sperm cells, the queen will have reduced fecundity and, consequently, there will be fewer workers to ensure plant pollination."
Assessing the risks posed by pesticides to species that are not their primary target, such as insects, focuses on the survival of these organisms. "Our study shows that to get a more complete picture of the impacts of these products, we also need to consider their sub-lethal effects. If we rely solely on survival, we could falsely conclude that a product is safe for insects, whereas it affects important traits such as fertility and fecundity", concludes Professor Giovenazzo.
The article published in Scientific Reports is signed by Andrew Brown, Verena Strobl, Peter Neumann and Lars Straub, of the University of Bern, Pierre Giovenazzo , of theUniversité Laval, Marilène Paillard, of the Centre de recherche en sciences animales de Deschambault, Andrée Rousseau, of the Centre de recherche en sciences animales de Deschambault and also a doctoral student at Université Laval, and Annette Van Oysteayen, of Royal Holloway College, University of London.
