New Meta-Analysis Examines How Landscape Fire Smoke Affects Insects
By Laura Kraft, Ph.D.
During the 2019-2020 bush fire in Australia, some entomologists wanted to calculate the area burned and the total number of insects that may have been killed during the blaze. While those calculations were based solely on the charred acres, a new research review published in September in Environmental Entomology attempts to map previous research on how landscape fire smoke, including smoke from bush fires like the one in Australia, affect insects—and where gaps lie in knowledge that new research could fill.
Yanan Liu, a Ph.D. student in geography at King’s College London, led the study. She and colleagues first searched through more than 9,000 articles that linked to their search terms related to smoke. After carefully parsing through the literature and removing articles on smoke from sources like cigarettes or vehicles, the team ended up with 42 total publications focused only on landscape fire smoke, which includes wildfires, prescribed burns, and agricultural residue burns. The selected studies spanned 15 different countries.
The papers represented show an inordinate amount of research that tracks how smoke affects beetles, with fewer papers focusing on effects on flies, bees, and butterflies. And, Liu’s team found, the general consensus is that there is no general consensus. Landscape fire smoke both positively and negatively affects insects in a variety of different ways. Says Liu, “I expected the smoke to repel all the insects or have a negative effect, but it depends on the insect order. For example, beetles are actually attracted [to landscape-based fire].”
For some of those beetles, though, including the red flour beetle (Tribolium castaneum) and the rice weevil (Sitophilus oryzae), smoke produced from burning cow dung and neem leaves caused high mortality. Smoke produced from rice paddy burning with high carbon dioxide levels at 5,000 parts per million may have also caused 50 percent mortality in the rice weevil and the lesser grain borer (Rhyzopertha dominica) in one study.
When it doesn’t cause death, particulate matter in smoke appears to block the antennal receptors in some insects, including bees. While European honey bees (Apis mellifera) famously show signs of decreased aggression in response to smoke (which is why beekeepers have long used smoke to work in hives), other stinging species, like the Sonoran bumble bee (Bombus pensylvanicus sonorous) and the western yellowjacket (Vespula pensylvanica), also show a dramatic reduction in attacks due to smoke. “We normally use smoke to repel bees if you want to get honey from the bees’ home … and when you use a smoker, the bees fly away from their nest. If this smoke influences some insects and changes their behavior, maybe smoke from the landscape fire or from wildfire changes the behavior of other insects,” says Liu.
There are some signs that landscape fire smoke may affect insect flight and migration. Some butterflies initiate flight in response to savanna fires, and painted lady butterflies (Vanessa cardui) show decreased flight performance when subjected to smoke. Other insects have been shown to delay their flights until sky conditions are clear, which may be due to smoke affecting the polarization of light that the insects would typically follow.
Some insects benefit from landscape fire smoke and are attracted to it. This includes wood-burrowing beetles from insect families Cerambycidae and Buprestidae. Some species of these beetles are attracted to smoke and rush back to damaged trees to reproduce at higher rates and colonize the newly damaged trees.
In addition, black army cutworm moths (Actebia fennica) doubled the amount of eggs they laid in response to the volatiles produced from burning vegetation due to increased reproductive hormones. And they weren’t the only butterflies to benefit. During severe forest fires in Borneo in 1997and 1998, most insect species declined, except the butterfly Jamides celeno (family: Lycaenidae) that increased its abundance out of all butterflies in the region from just 5 percent to 50 percent of the assemblage.
Despite having publications from five of the seven continents, one of the trends that the researchers found was a clear bias toward papers from the United States and Canada, with a moderate amount from Australia and far fewer stretched out over developing countries in Africa and Asia. While Western readers are familiar with many wildfires in those regions that hit major news outlets, Liu’s team points out that average levels of particulate matter—the small, often toxic particles making up smoke—are often even more highly concentrated in other regions; a study published last year identified central and west Africa and south and southeast Asia as regions most affected by landscape fire smoke globally. Clearly, there is need to increase research studying how landscape fire smoke affects insect populations in these understudied regions.
These few examples of how landscape smoke dramatically affects some insect populations, both positively and negatively, show that more research is needed to expand our understanding of the effects of landscape fire smoke—for a wider diversity of insects, in a broader range of behaviors, and over a larger geographic area.
In the meantime, Liu and her colleagues are now chipping away at some of these questions by studying how smoke affects painted lady butterfly flight behavior.
Laura Kraft, Ph.D., is an entomologist, science communicator, and world traveler currently based in Orlando, Florida. Email: email@example.com.