Air Pollution Disturbs Chemical Communication Between Plants and Pollinators
Wed, April 21, 2021

Air Pollution Disturbs Chemical Communication Between Plants and Pollinators


Insect pollination is crucial to agricultural systems and is as simple as insects, like bees, moths, and butterflies, fly from flower to flower to collect nectar. When an insect lands on a flower to feed, pollen grains stick to its body and these pollen grains are transferred on other flowers that they visit. This fertilizes the plant or flowers to produce seeds. Unfortunately, too much wind or rain and pesticides can reduce the pollination process. A new study also finds that high ozone air pollution can disturb the chemical communication between a plant and its pollinator.

How floral scents become less attractive to foraging insects

The team of researchers from the Max Planck Institute for Chemical Ecology in Jena, Germany shared that floral scents that pollinating insects depend on to locate the host plants that may be altered by the atmospheric oxidants, making these cues unrecognizable or less attractive to foraging insects. As a result, it will decrease the pollinator efficacy.

During experiments, the team showed that tobacco hawkmoths (Manduca sexta) lost their innate attraction to the scent of their preferred flowers (Nicotiana alata) when the scent had been changed by the ozone. They conclude that such oxidizing pollutants can disturb the interaction between plants and pollinators, a relationship that has evolved for millions of years.

The reason why the team used the tobacco hawkmoth as an insect model is that it is highly attracted to flower odors and it also uses its visual system when locating flowers. Study leader Markus Knaden explained that flowers that attract hawkmoth usually share certain compounds in their blend and are noticeable (visually) because of their bright white color.

Ozone-altered floral blend production

First, the team determined the compositions of the flower odors with and without the increased ozone content. They also used gas chromatography (GC) to know the concentrations of individual odor components. To generate the floral blends, the researchers used two one-day-old flowers of Nicotiana alata that had been grown under the same climate conditions and light as the moth. These flowers were placed in a box with an inlet of clean air flowing. Three-day old virgin male moths were then used to test their responses in the behavioral assays in a wind tunnel. This process enables the moths to investigate both the ozone-altered floral odor and the original floral odor.

Knaden said via that they were “very surprised, even shocked” that the innate attraction of moths to the floral scent was “completely lost” in the presence of oxidizing pollutants.

Brynn Cook from the Department of Evolutionary Neuroethology in Max Planck Institute for Chemical Ecology and the team said that ozone is a highly reactive chemical that can trigger a variety of health problems, including respiratory diseases in human. Now, such a chemical compound is found to influence the attraction of a pollination moth to the scent of their favorite flowers.

Moths learning the ozone-altered floral scents

This finding led to various questions, such as whether ozone in the air would prevent hawkmoths from finding their food source, or would it spoil their appetite. Will they still be able to find out that even polluted flower scent can still provide them nectar reward? To answer these questions, the team tested the moths’ ability to learn ozone-altered flower blends.

First author Cook said that although their team anticipated that the tobacco hawkmoths could learn new floral scents or learn the polluted floral scent of their host flower, what they found out was that they could instead learn the polluted floral blend in several ways. For instance, they could learn a polluted scent separate from a sucrose reward. The authors added that this type of learning could be important in insects’ ability to cope with the rapidly changing environments. What is especially relevant and noteworthy about such kind of responsiveness is that it happens not over evolutionary timescales but in real-time, Cook continued.

The team demonstrates that even if the tropospheric ozone disrupts the innate attraction of hawkmoth to the odor of its preferred flower, associative learning and visual navigation helped offset the disruption. Such a kind of ability can lessen the negative impact that air pollution may have on plant- or flower-pollinator systems.

Their study, which appeared in the Journal of Chemical Ecology, highlights that pollination is integral to maintaining healthy and diverse ecosystems. It contributes to global food production. Even the Food and Agriculture Organization of the United Nations states that more than three-quarters of the world’s food crops rely at least in part on pollination by insects and other animals.



Toxic pollutants affecting the pollinating insects

The authors said that even if tobacco hawkmoths can learn to depend on initially unattractive and ozone-altered scents to recognize their favorite flowers, air pollution still poses a serious risk to pollinators and pollination.

In April, a study that was published in the journal Tropical Conservation Science also shows that although the pollination ecosystem contributes to food security, little is known about the farmers’ awareness of the ecosystem service to ensure the conservation of pollinating insects. The following month, Statista Research Department also surveyed 2,809 respondents (from French households) and asked them if they know pollinating insects contribute to the reproduction of most plant species. It appears that half of the respondents said they were aware in general terms of the role that insects play in the reproduction of plants. Twenty-seven percent answered “yes, very precisely,” 18% said they know rather vaguely, and 5% said no.



Air pollution

According to Our World in Data, the burden of air pollution tends to be greater across both low- and middle-income countries for the following reasons: reliance on solid fuels for cooking (indoor air pollution) and increase of outdoor air pollution as nations industrialize. In 2017, countries with the highest death rates from air pollution per 100,000 population includes Papua New Guinea (245.3), Afghanistan (183.9), Madagascar (155.1), Somalia (165.8), South Sudan (156.2), Central African Republic (199.7), and Guinea (160.5).

Climate change and air pollution can have a far-reaching impact on our health and ecosystem. The Max Planck Institute study shows that both problems could impact our food supply and nutritional security. We need to take steps to maintain a greater diversity of pollinator habitats as this issue is directly linked to our well-being.