Insects and Society: Be less salty this winter season. Insects might thank you.

By Amanda Miloserny, Anne Howard, Anaís Juliano

If you grew up in a cold climate, you've probably had to deal with the unfortunate consequences that accompany the chilly weather. From the abundance of snow to the slick roads and sidewalks, winter affects key areas of transportation. We often find ourselves driving on slick midwestern roads, wondering why the city has not brought out the salt trucks and de-ice the slippery roads. Or when we were younger, having the chore of salting the pathway leading up to our front door. Needless to say, in the winter, we are quick to use salting roads as the solution to our icy problems. It was not until recently that we learned that salt that we often can’t wait to be put on roads and sidewalks has detrimental effects on surrounding insect ecosystems.

[1] Image of de-icing salts on a sidewalk.

In this blog post, we will examine Mangahas, McCauley, and Murray’s research from the University of Toronto on dragonfly larvae and their exposure to high concentrations of road salt. In the coming pages, we will define their research question, the methods they used, and the results they found.

Studies have shown that the salts that run off into water supplies can negatively affect the insects that rely on those water sources. Dragonflies, in particular, have experienced a negative effect with their larvae due to winter salts entering the water since dragonflies spend the start of their lives in streams and wetlands. Dragonflies are considered to be a top predator in the insect ecosystem, so any impact from de-icing salt would have a butterfly effect down the food chain.

In order to explore the potential harm de-icing salt would have on the larvae, Mangahas, McCauley, and Murray, researchers at the University of Toronto, used sub-lethal concentrations of salt that mirrored what nearby larvae might experience from a wintry season.

[2] Image of Anax junius, the dragonfly on which the study was conducted.

Like humans, larvae need a healthy immune system to respond to infections or parasites. Researchers wanted to see if the salt exposure would impair the larvae’s ability to combat an infection. First, they collected the larvae from a local pond and transported them back to the lab. The larvae were then kept in de-chlorinated water for three weeks before the experiment and fed with prey from the local pond. Then, the researchers separated the larvae into groups to explore the impact of the concentration of salt, duration of salt exposure, and also a control group with no exposure. The larvae were each put in a cup individually with one of the three conditions.

Researchers wished to see if the salt concentration impacted the level of melanization of a parasite they would simulate. The larvae’s ability to defend itself relies on covering the parasite with melanized blood cells. In order to simulate the parasite, the larvae were injected with sanded monofilament 1mm in length. Depending on the exposure length, the larvae either stayed in their concentration or were moved back to the de-chlorinated water, and then the monofilament was removed 96 hours later. Then, photos were taken of the monofilament to analyze and measure the melanin sections.

From measuring the melanin sections, the researchers could see that the larvae chronically exposed to high concentrations of salt had a decrease in their ability to defend against the simulated parasite. Those exposed to low concentrations at any duration and high concentrations at acute exposure had no significant impact on their ability to cover the parasite with the melanized blood cells. If a larva is exposed to high concentrations of de-icing salt for four days, its immune response to a parasite will suffer. This compromise could make the larvae more vulnerable to parasites that exist in the aquatic ecosystem. Additionally, the uptick in salt exposure could generate a stress response from larvae.

While this study narrows in on just dragonfly larvae, the impact of salt pollution can potentially burden all areas of freshwater ecosystems. Freshwater ecosystems are a key area of importance for us, too. From drinking water to fishing, humans utilize freshwater ecosystems all the time. We should then look to ways in which we can protect and promote freshwater ecosystem structure, diversity, and health. We must examine how our actions affect small communities to maintain rich biodiversity within our environment. However, it might not be practical to do away with using de-icing salts completely. Instead, we should be careful with when and how much we apply. Additionally, it might be time to explore alternative solutions to de-icing salt or look at ways to improve pavement to reduce runoff. Based on what we have learned, we know we will not be so quick to use salt as the holy grail of the winter season next time it gets icy out.

Insects and Society

Thursday, December 14, 2023

Be less salty this winter season. Insects might thank you.

The Buzzing Consequences of Microplastic Pollution

Report Abuse

Labels