Bee Declines: What Lies Underneath

Bees are a well-publicized and loved species of pollinator. Even children are taught from a young age the importance of pollinators in the world; therefore, as pollinators, bees are an essential component to terrestrial ecosystems– especially in the agriculture sphere (Goulson et al., 2015). The benefit is not just anecdotal: insect pollinators are found to benefit 75% of our current crop species while their ecosystem services are valued at $215 billion in the food production industry (Goulson et al., 2015). However, the news of “colony collapse disorder” has recently resurfaced, in addition to recent bee population declines throughout several parts of the world. What is causing these substantial declines?

Credit: Kees Smans – Getty Images

Habitat loss is the primary and most chronic factor that researchers attribute to bee population declines. Bees require adequate nutritional and floral resources during the adult flight season, in addition to undisturbed nest sites (Naug 2009; Goulson et al., 2015). The change in land-use patterns, which often includes habitat conversion into agricultural farmland, reduces the nutritional resources available to bees through the loss of natural and semi-natural flower-rich habitat.

Parasites and disease are another potential factor. Colony collapse disorder (CCD) is almost seen as mysterious, because it is often characterized by the sudden abandonment of hives by the adults, with no dead bees surrounding it. It was recently found that bees infected with a type of protozoan exhibit higher levels of hunger than their uninfected counterparts, suggesting that there is some energetic stress involved. Infected bees may be inclined to forage more often in order to satiate this hunger, but their decreased energetic states could make their foraging trips less successful, or inhibit their return to the hive at all (Naug 2009). The compounding effect of nutritional stress due to habitat loss or modification can further exacerbate the symptoms of this protozoan disease and therefore, CCD.

Pesticides and fungicides are a controversial side-effect of agriculture. Pesticides and herbicides, when used appropriately, can provide economical benefits to agriculture, but inevitably reduce the amount of flowers available to bees for pollination and nutrition, further creating resource deserts (Goulson et al., 2015). The exposure of bees to multiple pesticides and their direct effects are not well-known, and need to be further evaluated before mitigating actions can even be considered. However, neonicotinoids are a particularly nasty kind of insecticide and are heavily implicated in bee declines, able to persist in the soil and plant matter for a long time due to its water solubility (Goulson et al., 2015). Their extensive usage in agriculture suggests that bees have already been exposed to lethal and sub-lethal doses to these insecticides, but whether these losses are significant enough to impact population dynamics is poorly understood.

However, the interaction between multiple stressors is what is likely causing bee declines, not just one main factor (Figure 1). While the exact effects of these interactions are not yet well-researched, the mitigation of any of these stressors is bound to improve bee health overall. Increasing floral diversity and open land area available to bees can reduce nutritional stress and increase potential habitat space: this can mean planting more bee-friendly flowers in your own backyard (Goulson et al., 2015). Increasing habitat space, whether it be through restoring floral habitat within agricultural land or planting more flowers, means more nest site potential for bees. Encouraging more natural forms of pest and weed control can reduce the usage of harmful insecticides and herbicides, and reducing the spread of invasive species can also help save our bees, one step at a time.

Figure 1. Wild and domesticated bees can face the impact of stressors and their interactive effects. Adapted from Goulson et al. 2015.

References:

Goulson D, Nicholls E, Botias C, Rotheray EL (2015) Bee declines driven by combined stress from parasites, pesticides, and lack of flowers. Science 347: 1255957.

Naug D (2009) Nutritional stress due to habitat loss may explain recent honeybee colony collapse. Biol Conserv 142:2369-2372.

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