Pollinator problem: How honeybees could be making California fires worse

The unusual feeding habits of honeybees are likely leading to reduced populations of the Southwest’s dominant plant life, a new paper has found, suggesting the bees could be worsening southern California’s wildfires.

The study comes amid a rising popular interest in protecting “pollinators” due to their role in helping plants reproduce. But honeybees’ health may come at the expense of many of the plant and insect species they now live among, according to the findings published in the journal Royal Society B.

“There’s a decent amount of evidence to show that they’re competing with native insects for resources like pollen and nectar,” said first author Dillon Travis, who studies biology at University of California San Diego (UCSD).

Competition, however, may be just one downside. According to Travis’s research, honeybee populations may be making native ecosystems less genetically fit — opening the way for dangerous invaders.

Honeybees aren’t native to North America, although many wild bee species are. But the communal insects, which were introduced by European settlers, now play an important role in American agriculture, and have a particularly heavy presence in southern California.

How heavy? Around San Diego, honeybees made up 75 percent of all visits by pollinators to area flowers, previous research has found.

That primacy comes thanks to the combination of a robust beekeeping industry, widespread regional agriculture and large feral colonies of escaped honeybees.

Travis’s research suggests this level of honeybee activity is likely bad for native plant and insect species.

He found that flowers pollinated by honeybees create seeds with a far lower chance of growing to healthy adulthood than those pollinated by flies, butterflies and native bee species.

The reason why comes down to the honeybee’s unique social and foraging style, said Joshua Kohn, a UCSD entomologist and lead author on the paper.

Honeybees are rare among the broader bee species because of their penchant for living in huge, communal hives — the sites of the giant drone nurseries which require them to brew up their characteristic reserves of honey.

Honeybees meet the intense caloric needs of their larvae through a foraging style that can be described as a full frontal assault. 

Unlike native bees and butterflies, who will visit a couple of flowers on a plant before moving on to another, honeybees hit the same plants far more intensively. 

The members of a foraging swarm of honeybees work methodically and cooperatively, flower by flower, until they have drained the nectar from entire plants.

In and of itself, running out of nectar is not a bad thing for native plants. The nectar functions as the incentive for the bees to sick their faces into the flowers, which allows them to be coded with pollen that they can deposit in the next stop of their feeding journey.

Not all plants require insects to do this work — in a pinch, many can fertilize themselves.

But by transmitting pollen between plants of the same species, those insects help them maintain genetic diversity — avoiding the “intense inbreeding” that happens when plants fertilize themselves, Kohn said.

That is not a service that honeybees provide, however. Instead, Kohn said, “honeybees forage so methodically as they go flower to flower that they therefore mostly transfer self pollen” — pollen from the same plant.

In other words, they’re increasing the level of inbreeding — and therefore decreasing the genetic fitness of the next generation of plants 

The negative impact of honeybees on plant fitness isn’t a big problem for agriculture, despite the sector’s dependence on captive honeybees for fertilization, Kohn said. 

That’s because most farm crops are quick-dying annuals, and their important result is fruit, not the fitness of the next generation of seeds.

But for wild plants, fruits and flowers are just a means to securing the end that is viable offspring. 

Travis and Kohn’s research suggests that because honeybees focus so consistently on the same plants, they are breaking down that system across Southern California — in a way that may be reshaping the ecosystem as a whole.

In one scenario, that could be very good news for San Diego, a recognized biodiversity hotspot, Kohn said.

Because honeybees target the most dominant species for nectar collection, they might be a handicap on the growth of those species — one that would allow less dominant species to become a bigger share of the ecosystem, leading to greater biodiversity as a whole.

“That would be the happy result,” Kohn said.

The other result is considerably less happy, however. “It’s also possible that [honeybees] lower the fitness of the dominant species — and that leaves more room for invasives.”

And unfortunately for San Diego, the invasive best poised to take advantage of a pollinator-induced handicap to the dominant species are the ones most likely to bring wildfire into the ecosystem.

That’s because many highly flammable, fast spreading grasses, shrubs and trees in the region — like ryegrass, giant cane and eucalyptus trees — can reproduce without the help of pollinators.

These aggressive species can “clone” themselves via a creeping underground wave of roots, which send up a genetically identical crop of shoots above ground.

Some plants, like eucalyptus, perform a kind of biodiversity-destroying kamikaze attack on new environments. 

The Australian trees produce flammable oils, which encourage fires which can burn down entire forests — leaving green eucalyptus shoots to spread unchallenged across the burnt-out landscape, as National Geographic reported.

The paper as a whole suggests that the panic around honeybee survival may be misplaced, Travis said.

 “Many conservation efforts are focused on saving the honeybee, but they are not in any danger of going extinct. In fact, their numbers have been increasing,” he said.

“The organisms that do need our help are the native plants and bees,” Travis added.