Fewer bees and other pollinating insects lead to shrinking harvests

Many plants, from crops to carnations, can’t bear fruit or reproduce without bees, beetles, butterflies and other insects to pollinate them. But insect pollinator populations are declining in the U.S., in part due to pesticides, climate change, invasive plants and habitat loss. Rachel Mallinger, an assistant professor of entomology at the University of Florida, explains why these insects are declining and how homeowners can create pollinator-friendly gardens and yards.

The Conversation has teamed up with SciLine to bring you highlights from the discussion.

What types of insects pollinate?

Rachel Mallinger: Many different insects pollinate. Insects visit flowers for many purposes, often for food, to get nectar or pollen. Sometimes they visit flowers to mate or to lay eggs or as a refuge. Bees are the main pollinators for many plants, but flies, wasps, beetles and butterflies also play an important role.

How ecologically important are insect pollinators?

Mallinger: A small percentage of flowering plants are pollinated primarily by wind, but new research suggests that as many as 90% require animal pollinators. Although birds, bats and other mammals also pollinate, insects are the primary pollinators for the vast majority of these plants.

Without insects and their pollination, these plants would not be able to reproduce and we would see a dramatic decline in plant diversity and abundance. Without insect pollinators, these plants would not produce the seeds and fruits that feed many animals, including humans.

Have pollinating insect populations declined?

Mallinger: Recent studies have shown quite a dramatic decline in insects in general, and this has even been shown in protected areas. So we think that in highly developed areas the decline in insects is probably even more dramatic.

I study mostly native wild bees. Here in North America we have between 4,000 and 5,000 species. For many species we don’t know if they are declining. Of the species that we do have information about, it is estimated that about half are declining and about a quarter are endangered and possibly on the way to extinction.

The insect pollinators most at risk are those that are specialists: those that require truly unique, specialized food or nesting material. Also those that already have a limited range. For example, they are only found on islands or in a small area.

What about the economic importance of insect pollinators?

Mallinger: Crops pollinated by animals, primarily insects, account for about one-third of our agricultural output in terms of acreage. A study in the state of Georgia found more than US$360 million per year in crop pollination services provided by insects in that state alone.

What do insect pollinators need to be healthy?

Mallinger: In addition to pollen and nectar, some insect pollinators need additional food sources. For example, butterflies in the caterpillar stage need leaves from their host plants.

Other insect pollinators, such as wasps and flies, are carnivores in the larval stage. During this time, they must feed on small arthropods, such as spiders and centipedes, and insects.

In addition, they need nesting sites. Most insect pollinators nest underground, so they need soil that is relatively undisturbed, bare and accessible. Other pollinators nest in wood debris, stems and reeds. And some pollinators, such as butterflies, simply lay their eggs on host plants.

In addition, pollinators require environments that are free of toxins, so they require environments that are not regularly sprayed with pesticides, including insecticides.

Which stressors lead to a decline in pollinating insect populations?

Mallinger: I think there are five main stressors.

Land use change is one. This can be the conversion of wild areas to agriculture or to development.

Climate change is another stressor. It changes the average temperature that these pollinators experience and increases the likelihood of extreme temperatures and weather events. Hurricanes and floods can be really damaging and destroy pollinator habitat.

Third, there are the pesticides and other chemicals in our environment that are toxic.

Invasive plants can be really bad for pollinators. They can take over an area and replace the native plants that pollinators depend on. There are four of them.

And finally, pathogens and parasites.

All five of these stressors can interact. For example, climate change can increase the likelihood that invasive plant species, pathogens, and parasites will flourish. Land use change can also increase the likelihood that invasive species will flourish.

What can homeowners do to help pollinators?

Mallinger: Planting a variety of flowering plants for pollinators is one of the best things you can do. Try to have at least three plants blooming at any given time and look for a variety of flower colors and shapes. Different pollinators have different preferences. You can have flowers that are yellow, blue, purple, pink, red, and white.

In terms of flower shapes, plant some flowers that are flat and accessible to pollinators with small mouthparts. And also plant some flowers with medium-sized tubes, and some with long tubes.

Focus on native plants and try to find plants that are not just the common varieties you find in big box stores. Go to nurseries for native plants and search online for sources.

In addition, try to create nesting opportunities in your garden. If space permits, provide some woody debris for pollinators that nest above ground. This can include things like logs, stems, and reeds. Also, make sure your area is as chemical-free as possible. This also means limiting the use of pesticides.

Keep in mind that many pollinators that nest underground are not aggressive and are solitary. It is just one individual pollinator and her nest.

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