Radiofrequency electromagnetic fields reduce bumble bee visitation to flowers.

Insects are exposed to anthropogenic electromagnetic fields, especially in urban areas where these fields are widespread. They typically encounter these fields in two ways: when their nests are located in exposed areas or when they cross such fields in search of food sources or nesting materials. Recently, there has been an increase of publications in this emerging field of research on the effects of radiofrequency electromagnetic fields (RF-EMF) on pollinators. The authors of the current paper asked whether exposure to commonly used Wi-Fi frequencies could affect pollinators' flower visitation rates and thus their foraging behavior. If this radiation causes interference or has negative effects, it could make exposed areas in cities less attractive to bee species, which would represent a disruptive factor that could affect pollinators in highly developed areas.

The experiment was conducted during the summers of 2023 and 2024 at the State Institute of Apiculture, University of Hohenheim, Germany. The goal was to study the short-term effects of electromagnetic fields on the visitation rates and foraging behavior of honeybees and bumblebees. Although the electromagnetic treatment may affect the plants as well, the researchers carried out an experiment to investigate only its direct effects on pollinator visits. A total of 12 flower pots with 3 plants each were used: 6 with Lavandula angustifolia (n= 18) and 6 with Salvia species (n = 18). To ensure consistent exposure, the flower pots were placed 2 m from the radiation source.

A software-defined radio (SDR) simulated realistic Wi-Fi radiation at 2.45 and 5.8 GHz. In technical terms, the radiation source corresponds to commercially used Wi-Fi devices. The new experimental setup included repeated exposure and control tests carried out at close intervals. Alternating frequently between short exposure and non-exposure periods every four days controls for interfering factors, such as natural temporal variations. This alternation occurred throughout the 2-year experimental period, resulting in 21 EMF exposure periods and 23 non-exposure periods.

To determine the effects of different pollinators on flower visitation rates, insects were recorded on 92 days spread over 2023 and 2024. All plants in each pot were observed together. A total of 1,307 observations of flower pots were made. Each flower pot was observed for visiting pollinators for exactly 5 minutes. Flower visitation rates were analyzed using generalized linear mixed models (GLMM).

The authors recorded a total of 2,876 flower visitors, 50.4% of which were honeybees (n = 1,450) and 32.5% of which were bumblebees (n = 936) over the two years of the study. Overall, the main model revealed a significant negative effect of EMF on flower visits (EMF: 0.15, p = 0.0118). Closer analysis of the data showed that this effect was particularly evident among bumblebees (EMF: 0.25, p = 0.0029), which were observed significantly more frequently (28% higher) on flowers when plants were not exposed to RF-EMF. In contrast, this effect was not observed among honeybees (EMF: p > 0.05).

The use of electromagnetic fields to transmit information is enormously important for humans and technological progress. However, as these fields become more prevalent, we need to understand their potential impact on insects, especially pollinators. The experimental approach outlined here is suitable for determining weak EMF effects on pollinator flower visitation rates. This approach requires a large sample size and measurements taken over the course of days and months to control for environmental variability. Although no effect on honeybee visit frequency was found, the authors found that bumblebees reduced their visits when plants were exposed to RF-EMF. This suggests that bumblebees may avoid plants in urban areas when exposed to widespread Wi-Fi frequencies. Such avoidance reduces the availability of food sources and could force bumblebees to switch to other nectar and pollen sources. This could result in greater foraging effort and additional nutritional stress for these pollinators. At the same time, this could negatively impact plants by reducing their pollination rate.

Editor's notes:

This is an excellent semi-field study in terms of methodology, with conditions as close to reality as possible. Further efforts in this direction using other insects (although honeybees and bumblebees are certainly the most important pollinators) or radiation sources other than the Wi-Fi signal used here would be interesting, e.g. high-voltage transmission lines or mobile phone base stations. It is possible that the findings presented here may be applicable to other technical radio frequencies. The only question that would need to be answered is what distance from a base station would correspond to the 2-meter distance to the Wi-Fi router used here. (AT)