There are more than 20,000 known bee species on planet Earth, including the famous western honeybee, Apis mellifera, the domesticated species that has been managed by humans for thousands of years. But what would happen if all the bees suddenly disappeared?

Bees are currently facing a number of threats worldwide, including loss of habitat, parasites and pathogens, pesticides, climate change, declining forage quality and availability, and, in the case of domesticated bees in particular, poor management practices, according to Scott McArt, an entomologist at Cornell University.

Contrary to what many people believe, managed honeybees are not in decline. Nevertheless, huge numbers of hives are being lost every winter and spring. In fact, the numbers are only being maintained at relatively stable levels because beekeepers are becoming better at compensating for losses—a process that is very expensive and time consuming, according to May Berenbaum of the University of Illinois Urbana-Champaign.

When it comes to wild bees, population numbers are harder to document. But it is clear that many species are in decline across the world, with some even facing the threat of extinction.

For example, one 2017 study found that of the more than 4,000 bee species that are native to North America, nearly one in four among the species with sufficient data to assess (1,437) are imperiled and at increasing risk of extinction. It is important to note that not all wild bee species are in decline, with some populations remaining stable while many others are increasing in number and becoming more widespread.

Let's imagine a hypothetical scenario where all of the bees on Earth suddenly disappeared. One area where this would have a significant impact would be agriculture.

"If bees suddenly disappeared, there would be a profound impact on agriculture and the food we all eat," McArt told Newsweek.

Many crop plants rely on pollinator insects, such as bees, wasps and butterflies. When it comes to the number of global food crops, researchers have estimated that around three-quarters are partially or wholly reliant on pollinators, especially managed bees, and to a lesser extent, wild bees.

However, when it comes to overall crop production measured in tonnes, it is thought that around one third relies on pollinators to some extent. This is because we grow some crop plants more than others, and many of those that are produced in the highest quantities—staples such as cereals, for example—do not depend on them at all.

"If we lose all subspecies of Apis mellifera, we'd survive but we'd have to rely more on wild bees, which are having problems of their own, and other pollinators," Berenbaum told Newsweek. "Most fruits, nuts, and vegetables would be more expensive and much harder to find, because they'd be harder to produce.

"If you're talking about losing all 20,000 species of bees globally, we'd still survive because the bulk of calories people consume come from grains and cereals (for example, wheat, rice, and corn) or from vegetatively propagated crops (such as potatoes)—so we wouldn't starve per se."

However, bee pollination is very important—and difficult to replace on a large scale—for producing most of the crops that provide essential nutrients (particularly vitamins and minerals) and variety to the human diet (think spices and herbs, as well as stimulant crops such as tea and coffee), according to Berenbaum.

"So, if all bees were to go extinct, we may not be hungry but we'd likely be pretty sick and miserable," she said.

According to Christian Krupke, an entomologist at Purdue University, humans could conceivably survive without bees pollinating our crops but our diets would need to change dramatically.

"Bees pollinate most of our fruits, nuts, and vegetables—honeybees provide the bulk of this service," he told Newsweek. "Without them we would need to find another way to pollinate these many commodities and it would invariably be less efficient, resulting in lower quantities of more expensive food."

While some techniques have been developed to replace the pollination services that bees provide, scaling up these methods is challenging.

"There are many research projects and startup companies looking into robotic pollination of crops," McArt said. "Drones that release pollen from the sky, tiny robotic bees that brush against flowers, and even rovers dispensing soap bubbles containing pollen that coats flowers.

"Some of these technologies have been shows to increase pollination on a small scale, but none are currently effective on a large scale, and none are as good as bees. Bees are simply very good at pollinating. And wild bee pollinate for free! If we farm sustainably, the free labor will be there. If we don't farm sustainably, the free labor will leave."

Beside the impact on agriculture, the healthy functioning of natural ecosystems is also heavily dependent on the pollination services that bees and other pollinators provide, according to McArt. Around 90 percent of land plants are partially or wholly reliant on pollinators for reproduction, he said.

"If you look around, it's obvious we live in a green world where plants provide the foundation of ecosystems. Take away the ability/efficiency of plants to reproduce and ecosystems would be fundamentally disrupted," he said.

According to Robert Gegear, a professor with Worcester Polytechnic Institute's Department of Biology and Biotechnology, there are two very different contexts where bees function. While honeybees are important in agriculture, they provide no important services in the ecological context, he said.

"There they are competitors [with native bees] and they'll disrupt the system," Gegear told Newsweek.

If all the honeybees disappeared, it would have no negative effect ecologically speaking, he said, and would probably have a positive impact because honeybees are competitors for limited resources—pollen and nectar. Unlike honeybees, which form hives containing thousands of individuals, most native bee species are solitary.

If we start removing native bees, however, this would be a significant problem because they have a unique relationship with native flowering plants that supports ecosystems, keeping them healthy.

"If we lose native bees, we lose bee diversity. If we lose their functional role, which requires the plants that they pollinate, that's when we start losing things like wild biodiversity, ecosystem function and health. Because these plant-pollinator systems form the foundation of ecosystems."

On the ecological side, it is important to note that bees are just a part of a larger array of plant-pollinator interactions that includes other insects and animals, including flies, butterflies, moths and hummingbirds, to name just a few.

"Certainly, there are many bee-pollinated plants but that's only a small portion of flower-visiting animals that could function as a pollinator," Gegear said. "So, of the 200,000 species that visit flowers to feed on the nectar or pollen, around 20,000 are bees."

But this doesn't mean that removing native bees while other pollinators remained would have no impact.

"It's the diversity of native plant, or wild plant products native to that system, that's supporting the diversity of other wildlife," Gegear said. "As we start to remove those connections either from the animal side or the plant side, we'll eventually see ecosystem collapse and the loss of ecosystem services. These are things that we get from nature for free, like carbon sequestration and water purification, which all depend on healthy and diverse ecosystems."

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