Effects of ivermectin and imidacloprid on telecoprid dung beetles straight-line orientation behaviour

Abstract

As many arthropods, telecoprid dung beetles are deeply affected by anthropogenic pressures, including the extensive use of pesticides. Ivermectin, the main endectocide employed to treat livestock nowadays, drives population and species loss, and causes locomotion and sensory disorders in dung beetles. Imidacloprid, the major insecticide used to combat crop pests, is highly toxic towards pollinators, and disrupts foraging and flying performances. Numerous studies highlighted the detrimental effects of both pesticides towards non-target species, yet it is currently not known if they affect straight-line orientation abilities in telecoprids. Here, I evaluate the potential effects of pesticides on orientation performance of two ball-rolling species of telecoprids. I found that, despite no significant effects in the ability to maintain a set bearing, ivermectin caused a reduction in Ateuchetus semipunctatus rolling speed over time. Besides, findings suggest that higher concentrations of imida-cloprid impair the straightness of rolled trajectories in smaller Kheper lamarcki. Impacts on orientation behaviours could have repercussions on species survival and the entire ecosystem. This study is a first step towards our understanding of the effect of pesticides on oriented behaviours in dung beetles.

Popular Abstract

Think about a fresh, smelly, juicy pile of dung. Not appetizing? Well, dung beetles would fight to even get a tiny piece of this feast.

When it is time to feed, hundreds of dung beetles fly over to a dung pile, each competing fiercely to try to get their share of the food. To avoid getting their food stolen by others, ball-rolling dung beetles have a trick: they shape a portion of the dung into a ball and roll it away from the dung pile, until they find a safe place to bury their precious loot in the ground to enjoy it in peace. By removing and relocating dung, they also ensure the good health of the soil.

The most efficient way to escape the competition at the dung pat is to steer in a straight path away from it. To do so, these rollers set their internal compass by using cues in their environment, and steer along a bearing. These can be visual cues, such as the position of the sun in the sky, or mechanosensory cues, like the direction of the wind.

However, like many arthropods, dung beetles also suffer from a number of threats because of us humans, including the exposure to pesticides. Pesticides can be found everywhere in their environment, from the food they eat to the soil they walk on and dig in. Yet, we do not know the effect of pesticides on dung beetle behaviour, especially on their orientation skills, and this is what I aim to investigate in my thesis.

To do that, I went to Sardinia and South Africa to find and collect beetles from two diurnal species of ball-rolling dung beetles. Back in Lund, I expose them for 10 days to two very common pesticides, via the dung or through soil. I measured their rolling performance before, during and after exposure, to understand how their orientation abilities are affected over time.

My two species showed different responses to pesticides. The sardinian dung beetles were less active as more pesticide was present in their food. I also found that the beetles were rolling their balls more slowly compared to beetles feeding on lower concentrations of pesticide. This means that they are less efficient at rolling their ball. In nature, they would take more time to escape the dung pile and thus be more prone to competition. However, I did not find a decrease in activity or rolling speed for the south-african species, which could mean that the two species have different sensitivities to the pesticide. Besides, when exposing the south-african species to high concentrations of pesticides in the soil, I found that beetles of smaller body sizes were less able to roll straight compared to larger ones. This happened while orientating with a simulated wind cue in the lab, which could mean that smaller body-sized beetles would have trouble setting their compass with mechanosensory cues because of pesticides. Remarkably, both species were able to remain quite precise in their chosen bearing despite the pesticides in their food or in the soil.

This is a first step towards a better understanding of the effect of pesticides on dung beetles and insect orientation behaviour. It is a novel field of research, so there is still plenty more to discover!

• author: Deck, Lena
• supervisor: Claudia Tocco; Marie Dacke
• organization: Degree Projects in Biology
• course: BION03 20241
• year: 2025
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9188127
• date added to LUP: 2025-05-07 13:34:50
• date last changed: 2025-05-07 13:34:50