Bat response to experimental insecticide application against a defoliating moth in mixed oak forests
| Authors: | Sophia Hochrein, Andrew M. Liebhold, Soyeon Bae, Bernadette Wimmer, Benjamin M. L. Leroy, Sebastian Seibold, Wolfgang W. Weisser, Jörg Müller, Maike Huszarik |
| Year: | 2025 |
| Type: | Scientific Journal |
| Station: | Northern Research Station |
| DOI: | https://doi.org/10.1111/1365-2664.70104 |
| Source: | Journal of Applied Ecology |
Abstract
1. Bats are important but threatened insectivorous predators, making them a core group to consider when weighing the risks and benefits of insecticide use for combating pest outbreaks. Bats may benefit from open spaces created when insect pests defoliate tree canopies. Applying insecticides could also make treated areas less attractive to bats by lowering insect availability and increasing canopy densities.
2. Here, we examined the effects of a one-time insecticide treatment of oak forest plots with tebufenozide under outbreak and non-outbreak scenarios of the forestry pest species Lymantria dispar in a full-factorial and well-replicated field experiment. The activity of all bats and of closed-, edge-and open-space foragers was measured at 44 plots over 3 years using autonomous acoustic bat recorders. We simultaneously estimated the biomass of available flying insect prey using light trapping and quantified changes in tree canopy density using satellite-based radar.
3. Contrary to our expectations, we found higher bat activity in insecticide-treated plots than in untreated plots, including plots with predicted L. dispar outbreaks. There was no overall prey reduction at treated plots. Moreover, the high canopy density, particularly at treated plots, likely promoted biomass of non-moth, non-beetle flying insects. This suggests that bats, especially open-space foragers, responded to the increasing availability of other insects at treated plots with a higher canopy density, rather than to a decrease in prey availability.
4. Synthesis and applications: L. dispar drastically decreased the canopy density of outbreak plots, whereas insecticide treatment protected the tree canopy from defoliation. However, bats were not promoted by lower canopy density, and there was no decrease in insect prey availability between plots. Bats continued to be active at forest plots treated with tebufenozide, which may be due to insect prey harboured in the denser tree foliage at these plots. Overall, we did not observe the expected strong negative response of bat activity to tebufenozide treatment when using acoustic bat monitoring. However, there may be other risks to consider, such as pesticide exposure and food web alterations, which must be evaluated using different methods.