Trouble for the Food Supply

This column was published in the Cranbrook Daily Townsman Tuesday September 21, 2010.



So how did your garden do this year? Generally cool temperatures have kept many tomatoes green and not helped many crops, especially berries. On the other hand, cool and regular showers has our lettuce still going strong when it is normally virtually toasted by early August. We’re enjoying a second go-round of peas and were enjoying a bumper crop of beans until the frosts of early September took them out.

But more than just good weather and careful tending is required to pull off a successful garden. Many crops, wildflowers and other plants are reliant on insects for pollination in order to successfully bear fruit and viable seeds. Bees provide the vast majority of these pollination services to agriculture and natural ecosystems. Honey bees can increase yield in 96% of animal-pollinated crops and insect pollination in general (mostly bees) is necessary for 75% of human crops worldwide. If you like berries, coffee, nuts and other foods, you want bees.

But recent declines in bee populations around the world raises significant concern for the future for both agricultural productivity and wild plant communities. The majority of agricultural and apicultural (bee keeping) scientists now agree that significant declines have occurred in honey bees world wide. Some estimates suggest a 59% loss of honey bee colonies in the USA between 1947 and 2005.

And domestic bee populations decline, what is going on in wild bee populations are also thought be suffering widespread losses. Recent work in Illinois found half the bumblebee species there were either extirpated (no longer existing in certain areas, but present elsewhere) or had suffered declines. The trouble is we don’t know much about wild bees. To document a decline you need both current population estimates and from some time in the past. We just don’t have much of that data. Where the data are available, the news is not good.

A recent review of pollinator declines, published in the journal Trends in Ecology and Evolution, reports on evidence of the decline and what is driving it. Habitat loss is indicted as a key driver of wild bee declines. As natural ecosystems are urbanized or otherwise altered, most native bees suffer along with other wildlife species. Hand-in-hand with bee declines are losses of plant diversity. In some cases this becomes a chicken-and-egg scenario. Many plants rely on bees for pollination and reproduction and vice-versa. If one is removed from the ecosystem the other also fails. Trying to figure out which declined first is difficult and not always

Electron micrograph of Varroa destructor mite on a honey bee

Intensified agricultural activity is another driver. Insecticides in particular kill bees directly, while herbicides and fertilizers are implicated as reducing food availability to bees and other pollinators.

One cause of bee declines that has received media coverage is the introduction of a parasitic mite from Asia. The Varroa mites latch on to bees and feeds on the insect’s hemolymph (essentially insect blood). Further weakening the bee are various viruses transmitted by the mite so that entire bee colonies can be wiped out. Some estimates suggest that all feral honey bee colonies in the Europe and the United States have disappeared as a result of Varroa mites.

Varroa mites on honey bee pupae.

Climate change may also impact bees. Mismatches in bee emergence and plant flowering can result in reduced productivity for both bee and plant. All these drivers may act independently or in an additive effect that combine to drive local declines farther and faster. The consequences for agricultural and food production are significant, though they can rent travelling honey bee colonies at the time when pollinated is needed most.

Most home gardeners can’t justify that level of cost. Worrying about late and early frosts is enough of a challenge. Adding in doubts about whether your garden will be pollinated is just one more uncertainty.