Experts on Camera

Dr. Rachel Mallinger: Pollinator gardens

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Many flowering plants that humans consume and admire could not reproduce or bear fruit without insect pollinators, but evidence suggests that populations of these animals are declining in the United States.

On April 1, 2024, SciLine interviewed: Dr. Rachel Mallinger, an assistant professor of entomology at the University of Florida. See the footage and transcript from the interview below, or select ‘Contents’ on the left to skip to specific questions.


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RACHEL MALLINGER: I am Rachel Mallinger. I’m an assistant professor in the department of entomology and nematology at the University of Florida, and I study pollination—both of crop plants and also of wild plants—and the pollinators, primarily insects that do the pollination. My focus is on native wild bees, but we also in my lab study any insects that pollinate, that includes a variety and diversity of insects, and we study their behavior, their conservation, and their general biology.

Interview with SciLine

What kind of insects pollinate?


RACHEL MALLINGER: A lot of different insects pollinate: anything that will visit a flower. And insects visit flowers for different purposes, often for food, to get nectar, or to get pollen, but sometimes they’ll visit flowers to mate, or to lay eggs, or as refuge. The insects that pollinate include bees. Those are primary pollinators for a lot of plants, also flies, wasps, beetles, butterflies, and even additional insects beyond those groups, but those are the primary groups.

What can you tell us about the ecological importance of insect pollinators?


RACHEL MALLINGER: About 85% of flowering plants require animal pollinators. The remainder, the 15%, would be pollinated primarily by wind. About 85% of these flowering plants are pollinated by animals, which can include things beyond insects, things like birds, bats, other mammals, but insects are the main pollinators for the vast majority of those plants. And pollination is a part of how these plants reproduce. So without insects and without pollination, these plants would not be able to reproduce, and we would see a dramatic decline in plant diversity and in plant abundance. But there are other consequences if we didn’t have insect pollinators. Not only would these plants not be able to reproduce, but they wouldn’t produce the seeds and the fruit that feed other animals, things like birds, mammals, a variety of animals that feed on seeds and fruit.

What can you tell us about the economic importance of insect pollinators?


RACHEL MALLINGER: Roughly 75% of crops are pollinated by animals, with insects being the most important of these animal pollinators. The 75% of crops that rely on animal pollinators, primarily insects, that makes up about 1/3 of our agricultural production in terms of acreage. And studies have valued this at, for example—in the state of Georgia alone—over $350 million per year in crop pollination services provided by insects. Globally, our best estimates are over $150 billion dollars per year in insect pollination services.

What sorts of resources and habitat do insect pollinators need to be healthy?


RACHEL MALLINGER: Insect pollinators need food, and this is primarily in the form of pollen and nectar that flowers provide. But some insect pollinators require additional food sources. For example, butterflies, as adults, they’ll visit flowers for nectar and feed on nectar, but in the caterpillar stage, they need foliage from their host plants. Other insect pollinators, like wasps and flies, need different little arthropods and insects to feed on in the larval stage. They’re carnivores in the larval stage. So different pollinators have different food requirements, including pollen and nectar from flowers, but also including things like foliage, or little arthropods, and insects. Beyond that, they need nesting habitat. The majority of our insect pollinators nests below ground and so they need ground that is relatively undisturbed, bare, and accessible. Other pollinators nest in woody debris, stems, and reeds. And some pollinators, like butterflies, for example, just lay their eggs on host plants. Additionally, pollinators need environments that are free from toxins. So they need environments that are not regularly sprayed with pesticides, including insecticides. Food, nesting habitat, and protection from toxins you can think of as the three main needs.

What can you tell us about the declines in insect pollinator populations?


RACHEL MALLINGER: There have been some recent studies that have shown pretty dramatic declines in insects generally, and this has been shown even in areas that are relatively well preserved in conservation spaces. Thus, we think that in highly managed, highly developed areas, insects declines are probably even more dramatic. I study primarily native wild bees, and within native wild bees—here in North America—we have between 4000 and 5000 species. Of those: Many species, we don’t know if they’re declining. Of the ones that we do have some information for, it’s estimated that about half are declining, and about a quarter are imperiled and potentially on the road to going extinct and being endangered. We have pretty good evidence for the declines of some bumblebee species, and also some bees in Hawaii, and some are even listed as federally endangered. The insect pollinators that tend to be most at risk are ones that are specialists that require really unique, specialized food or nesting resources. Also ones that already have a limited range. For example, maybe they are found only on islands or in a small area. Those make the insect pollinators much more vulnerable to declines.

What sorts of stressors are leading to declines in insect pollinator populations?


RACHEL MALLINGER: I would say there are five main stressors. Land use change is a major stressor. This can be the conversion of wild lands to agriculture or to development. Climate change is another stressor, it changes the average temperature that these pollinators are experiencing. It also increases the chance of extreme temperatures and also increases the chance of extreme weather events—things like hurricanes, flooding that can be really detrimental—can destroy the habitat for pollinators. Thirdly, pesticides and chemicals more broadly, there are other chemicals and toxins in our environment beyond pesticides, but pesticides are a primary one. Invasive species, fourthly, so invasive plants can take over an area and replace the native plants that pollinators depend on, and this can be really detrimental for pollinators. And then, finally, pathogens and parasites. And these things can interact. For example, climate change may increase the likelihood of invasive plant species or of pathogens and parasites. Land use change can also increase the likelihood of invasive species, for example, but those are the five main stressors for pollinators broadly.

How do stressors that impacts native pollinators and commercial honeybees compare?


RACHEL MALLINGER: Commercial honeybees have a few unique stressors, for example, long-distance transportation. They’re carted all around the country to pollinate crops, and that’s a unique stressor. I would also say pesticides might be a more significant stressor, both because there are some that are applied directly to the hive, but also honeybees are often placed in environments like crop fields where pesticides are routinely applied. For wild pollinators, I would say land use change is probably the biggest stressor. Because we can’t pick up these wild pollinator populations and just move them to a better habitat. They’re really dependent on the natural native habitat. And then there are other stressors, like, I would say, climate change probably affects managed pollinators and wild pollinators pretty equally.

What sorts of strategies can homeowners and land managers employ to provide habitat and resources for pollinators?


RACHEL MALLINGER: Pollinators need flowering plants. So providing flowering plants for pollinators is one of the best things that you can do. Focus on native flowering plants. Focus on planting in clumps, having a high density of floral resources available for pollinators. You can plant additional food resources: for example, for butterflies, host plants. Also, managing your area to be as chemical-free as possible. This includes reducing pesticide use, especially on flowering plants and when plants are in flower. I also think it’s important to remember that advocacy and supporting conservation are important for pollinators. There are many pollinators that you can find in your yard and that you can find in developed spaces. But there are a number of specialist pollinators that you’re unlikely to find in your yard no matter what you do to provide for them. And they really require specialized natural habitat. So supporting the conservation of those natural habitats is also important—in addition to what you do in your own yard or in your own land.

What advice do you have when it comes specifically to gardening for pollinators?


RACHEL MALLINGER: I would say plant a diversity of flowering plants. Aim to have at least three plants flowering at any given time, and look for a diversity of flower colors and shapes. Different pollinators have different preferences. You can have flowers that are yellow, blue, purple, pink, red, and white. So having a diversity of colors is really important because, again, different pollinators have different preferences. In terms of floral shapes, have some flowers that are flat that are accessible for pollinators with small mouthparts. Have some flowers that have medium-length tubes, and then you can have some flowers with long tubes. Having that diversity of colors and shapes will provide for different pollinators. Focus on native plants, and try to seek out plants that might not just be the common types that you would find in the big box stores. Go to native plant nurseries, seek out resources online. Additionally, try to have nesting habitat in your garden. This includes ground that is accessible—it doesn’t have to be entirely bare—but it shouldn’t have a cloth or a plastic barrier on it. And if you see nests, try to let them be. Don’t disturb them. Keep in mind that many pollinators that nest below ground are not aggressive and are solitary. It’s just one individual pollinator and her nest. It’s not a large aggregation. Preserving those nests will help to conserve those pollinators. And additionally—if the space allows—have some woody debris around for the pollinators that nest above ground. This can include things like logs, stems and reeds.

What advice do you have for reporters covering insect pollinators?

[Posted April 1, 2024 | Download video]