Climate Change is Affecting Plant-Insect Interactions

Author: Torin Hicks, Edited By: Emilyann Ashford

Nature and its beauty are a result of a complex web of mainly stable interactions between organisms and their environment.  The existence of animals like frogs comes from their ability to compete well in a specific niche for energy.  At the base level of every energy driven interaction are plants.  Most plants don’t consume, but instead generate energy by photosynthesis—utilizing inorganic materials such as carbon dioxide and water with the help of sunlight.  Higher level consumers, i.e., a sheep that eats a plant, or a wolf that might eat a sheep are dependent on the ability of plants to generate energy to move into the food web.  These are called trophic levels.

A trophic level is the position that a species is present within a food chain, plants and insects are at the very bottom, and any change in their dynamics can be seen having a bottom up effect on the environments they inhabit. One way climate change has affected this dynamic is by altering the interactions between plants and insects—namely by changing pollination and herbivory.

Change in Pollinator-Insect interactions

Pollination is a process in which the male gamete of the plant, the pollen, meets with the anther of a plant—fertilizing the egg and later developing into a seed.  Some plants can self-pollinate, whereas others are obligate; this just means that they require a pollinator to introduce a pollen grain to their anther from a different plant to reproduce.  Even self-pollinating plants benefit from pollination since fertilization across individuals results in greater genetic diversity (FS FED).  

Climate change affects pollination in a few different ways. For example, plants and insects can change their phenology. This means that they can either behave or even look physically different, which can result in several things like mismatches between a pollinator and the anther, or inability to be pollinated because of a change in flowering timing. There are other anthropogenic stressors that impact pollinators which are worsened by climate change such as: habitat loss, disease, and the spread of invasive species (UCSUSA).

Affected Pollinators

There are numerous examples of pollinators which have been impacted by climate change rooted shifts in plant-insect interactions, a classic example being the honeybee.  Honeybees are an extremely economically valuable species, contributing an estimated 117 billion USD annually (9).  Climate change has resulted in an increase of extreme droughts and wet seasons. Acacia-flowers, which the honeybee forages from, decrease their nectar yields in particularly wet seasons—causing honeybees to starve in some instances. On the contrary, drought reduces the production of nectar by lavender, again either starving the honeybee or causing them to find plants with better yields (5).

Another Pollinator that’s been affected by climate change is the Tiger Moth.  You might not think of moths as important pollinators, but they are.  In fact, a variety of other insects are pollinators too, such as wasps, beetles, and butterflies. Some species of tiger moth are important pollinators of Atlantic forest plants, like orchids.  Climate change has drastically altered tiger moth species’ ranges (the spaces they inhabit), tending to move to colder environments. The result of these changes have led to the shrinkage of Tiger Moths’ ranges, and in turn species that rely on them as pollinators losing their diversity and robustness (3).

The figure above depicts the loss in species richness from 1950-2000 (present) and 2051-2080 (future) of the tiger moth in the Atlantic Forest Biodiversity Hotspot, Brazil with two different modeling methods and climate models. Overall, there’s a decrease in species richness (3).

The figure above depicts the loss in species richness from 1950-2000 (present) and 2051-2080 (future) of the tiger moth in the Atlantic Forest Biodiversity Hotspot, Brazil with two different modeling methods and climate models. Overall, there’s a decrease in species richness (3).

Changes in Insect Herbivory

To begin, herbivory is a specific kind of predation, in which living plant tissue is consumed by any animal. In the same way that non-insect animals are having their feeding habits altered by global climate change, insects are too. There are obvious direct effects, such as certain insects seeing increased success due to milder winters, or an increase in range of insect herbivores due to more favorable conditions. Not only are there direct effects—indirect effects are also very prevalent. For example, increased summer rainfall, which results in increased vegetation cover, can lead to an increased abundance of Auchenorrhyncha—which is a kind of cicada that feeds on plants (6).

Affected Insect-Herbivores

There are plenty of examples of insect herbivores whose interactions with plants have been altered due to climate change. One such example is the pine processionary moth. The adult pine processionary moth itself does not feed on pine needles or pine trees, but its larvae do. Pine processionary moth larvae eat the pine needles of specific conifers during winter nights, causing the formation of crooked trunks that permanently injures the tree. Milder winters have altered pine processionary moth larvae’s behavior to allow for increased feeding activity during the winter months (8). Not only this, but these increased winter temperatures have also increased the range of the pine processionary moth, allowing for even more herbivory (1).

Another good example of an insect herbivore’s changing behavior with plants in-part due to climate change is Doratifera quadriguttata. They are an insect herbivore that feed on: red mangrove, brush box, water gum, acacia, and eucalyptus. The increase in atmospheric carbon dioxide concentration is predicted to influence the quality of plant leaves.  Eucalyptus herbivores are likely particularly sensitive to this effect since the rise in carbon dioxide decreases their already low leaf nitrogen concentration, increasing feeding events to make up for the lowered nitrogen concentration in the herbivore’s diet from lower quality leaves (7).

This isn’t to say that every outcome of climate change leads to increased herbivory in every insect herbivore, but it does indicate that certain insect herbivores are clear winners—ones that benefit from extreme drought, wetter summers, and warmer milder winters (6). Not only this, but certain plants, like those losing nitrogen content from rising carbon dioxide (eucalyptus), are clearly suffering from climate change driven herbivory.  

Putting it All Together

Plant-insect interactions are strongly disproportionately impacted by global climate change, and as such they are very responsive—and easily observed.  Global climate change indicates to us that insects tend to be a clear winner in shifting plant-insect interactions, with their high reproduction rate and fast response times they tend to outpace plants’ response to climate change, which plant range and coverage has suffered for (4).

An all-too-familiar effect widely known is the impact global climate change has had on pollinators, the function of which are not only important for maintaining plant diversity, but also yield great economic value. They’re a part of food security and directly impact 75% of human grown crops (10).  Mitigating the impacts climate change has would be crucial to returning stability at the base level of the food web, which has numerous bottom-up effects in so many different ecosystems.

The figure above shows pressures between various biological stressors that all play an important role on pollinator-plant interactions (10).

The figure above shows pressures between various biological stressors that all play an important role on pollinator-plant interactions (10).

Solutions and Mitigation

There’s plenty that can be done to mitigate the impacts of climate change.  To start, globally we can try and reduce the overall carbon emissions and footprint that we leave, which directly mitigates the rate at which both global temperature and atmospheric carbon dioxide concentration will rise (2). On an individual level you can do things like driving an electric car or hybrid rather than a fossil fuel burning one or using less electricity.  This will lead back to things like harsher winters, making it harder like insects like the pine processionary moth to feed. This decrease in atmospheric carbon dioxide content could also see the return of higher nitrogen concentration in plants like the eucalyptus which could reduce the increased eating of their leaves by herbivores like Doratifera quadriguttata (7).

Mitigating the impact of climate change will also lower the rate of range shifts for insect herbivores, which allows the plant life a longer time to adjust. Lastly, we’ll see a decrease in the stressors many pollinators face, like habitat loss and increased competition (10). The damage to the environment is already done as far as global change goes, however, there are different more optimistic models which paint a more hopeful and less drastic picture for loss in biodiversity if we can achieve them.

Works Cited

  1. Battisti, A., Stastny, M., Netherer, S., Robinet, C., Schopf, A., Roques, A., & Larsson, S. (2005). Expansion of geographic range in the pine processionary moth caused by increased winter temperatures. Ecological applications, 15(6), 2084-2096.

  2. Betsill, M. M. (2001). Mitigating climate change in US cities: opportunities and obstacles. Local environment, 6(4), 393-406.

  3. Ferro, V. G., Lemes, P., Melo, A. S., & Loyola, R. (2014). The reduced effectiveness of protected areas under climate change threatens Atlantic Forest tiger moths. PLoS One, 9(9), e107792.

  4. Hodkinson, I. D., & Bird, J. (1998). Host-specific insect herbivores as sensors of climate change in arctic and alpine environments. Arctic and Alpine Research, 30(1), 78-83.

  5. Le Conte, Y., & Navajas, M. (2008). Climate change: impact on honey bee populations and diseases. Revue Scientifique et Technique-Office International des Epizooties, 27(2), 499-510.

  6. Masters, G. J., Brown, V. K., Clarke, I. P., Whittaker, J. B., & Hollier, J. A. (1998). Direct and indirect effects of climate change on insect herbivores: Auchenorrhyncha (Homoptera). Ecological Entomology, 23(1), 45-52.

  7. Murray, T. J., Tissue, D. T., Ellsworth, D. S., & Riegler, M. (2013). Interactive effects of pre-industrial, current and future [CO 2] and temperature on an insect herbivore of Eucalyptus. ---Oecologia, 171(4), 1025-1035.

  8. Netherer, S., & Schopf, A. (2010). Potential effects of climate change on insect herbivores in European forests—general aspects and the pine processionary moth as specific example. Forest Ecology and Management, 259(4), 831-838.

  9. Reddy, P. R., Verghese, A. B. R. A. H. A. M., & Rajan, V. V. (2012). Potential impact of climate change on honeybees (Apis spp.) and their pollination services. Pest Management in Horticultural Ecosystems, 18(2), 121-127.

  10. Vanbergen, A. J., & Initiative, T. I. P. (2013). Threats to an ecosystem service: pressures on pollinators. Frontiers in Ecology and the Environment, 11(5), 251-259.

Emilyann Autumn