Effects of mixed neonicotinoid and fungicide exposure on the pollen collection and colony development of Bombus terrestris

Abstract

Bumblebees are essential pollinators for a wide range of plant species and thus essential for global ecosystems and food security. However, recent declines in their populations have made understanding their underlying causes necessary. One of those causes is the application of pesticides in agricultural landscapes. The toxicity of these pesticides is commonly assessed in isolation, which oftentimes fails to account for synergisms between pesticide mixtures that pollinators are often exposed to. In honeybees one of those synergisms that has been observed is between ergosterol biosynthesis inhibiting (EBI) fungicides like tebuconazole and neonicotinoids like acetamiprid and imidacloprid. Acetamiprid is the last remaining pesticide approved for outdoor use in the EU, since it is commonly shown to be less toxic to pollinators that other neonicotinoids like imidacloprid. However, the basis of research for that assumption is mostly focused on honeybees (Apis mellifera) and without taking into account synergisms. Therefore, this study aimed at characterizing effects of acetamiprid, tebuconazole and a possible combined effect on the buff-tailed bumblebee Bombus terrestris, with the well-studied neonicotinoid imidacloprid as a baseline for effects. Specifically, effects on colony development, pollen collection, and colony performance were evaluated. However, due to an insufficient degree of exposure to and possibly a short period of observation, no effect of acetamiprid and tebuconazole could be documented. The only effect seen was imidacloprid decreasing the amount of pollen collected by foragers on a foraging bout. Other covariates like the initial weight of the colonies, their batch and site, were found to affect colony development and colony performance. This being said, future research addressing those methodological problems is promising to understand the complex relationship between combined pesticide effects, foraging behaviour, and colony development.

Popular Abstract

It’s time to BeeReal!

I don’t know about you, but I personally enjoy having food. Pesticides? Not so much. However, they are an important part in modern agriculture, protecting crops from many pests, like fungi and insects. But sadly, those pesticides don’t just harm pests, but also many other plants and animals, like bees. That is why in my master’s project I wanted to research some of those effects on my favorite kind of bee. The very adorably named buff-tailed bumblebee B. terrestris.

Imagine you are a bumblebee, the cutest and fluffiest of all bees. You live in loosely organized colonies with your mother (the queen) and up to 350 of your sisters. You all work together, on the many chores you have to do around the colony. You help raising more of your sisters, cleaning the hive, or going out, foraging for pollen and nectar, while pollinating many plants. Life is good. But more and more of those flowers you need to survive disappear, and the ones that are still left often contain strange poisons that make you forgetful, clumsy, and maybe even change what flowers you like. All of that makes it harder for you to collect enough food to keep the colony alive, and maybe even next year, when some of your sisters are supposed to found their own colonies, they are too weak to do so. Which means that less and less of you are around each year, leaving many of the plants that rely on your hard work unpollinated and unable to produce fruit. This process has been happening to bumblebees worldwide for decades now. Changes in the environment and pesticides have caused declining numbers year after year. That is the reason why we humans must understand how pesticides affect pollinators. Because without them pollinating so many of our crops, we can’t produce nearly as much food as we do now.

This is why for my thesis, I was looking at the effects that the pesticides acetamiprid, and tebuconazole have on bumblebee colonies. As a comparison, I included imidacloprid, which is known to have multiple effects on bumblebees, including reduced colony growth and foraging efficiency. It can even alter the foraging preferences of exposed bumblebees! I wanted to know if exposure to these pesticides prevented the colonies from growing, if fewer worker bees survived, if they produced fewer larvae, and if they collected pollen from other plants, and that change would affect the nutritional value of the pollen. To study this, we placed 32 colonies of bumblebees around the ecology building during the summer and watched them grow and collect pollen for 3 weeks.

However, we did not see any change in most of the measured variables. As it turns out, our bumblebees got off too easy. The problem was that we underestimated the size of the colonies and did not give them enough pesticides for them to be really affected. But we are still not giving up, which is why we are already planning to do an adjusted study again this summer, after which we will hopefully know more.

Master’s Degree Project in Conservation Biology, 45 credits 2024
Department of Biology, Lund University

Advisor: Lina Herbertsson
Department of Biology, Lund University

• author: Heck, Alexander
• supervisor: Lina Herbertsson; Ola Olsson
• organization: Degree Projects in Biology
• course: BION02 20232
• year: 2024
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9154610
• date added to LUP: 2024-05-27 14:17:20
• date last changed: 2024-05-27 14:17:20