Page 273 - Environment: The Science Behind the Stories

Conserving Pollinators,
Controlling Pests

One of the most important facets of agriculture is how we handle
the many organisms that interact with our crops and livestock.
Some organisms are “pests” that pose threats to agriculture,
such as insects that feed on crop plants, pathogens that attack
livestock, or weeds that compete with crops. Other organisms
are beneficial to agriculture. The insects that pollinate crops are
among the most vital (yet least appreciated) factors in our food
production. Pollinators are the unsung heroes of agriculture. If
we are to attain sustainable agriculture, then we will need to
find safe and effective ways of limiting losses to pests, and we
will need to better conserve the insects that pollinate our crops. Figure 10.17 Beekeepers bring hives of honeybees to
farmers’ crops when it is time for flowers to be pollinated.
We depend on insects to pollinate crops

Pollination (p. 98) is the process by which male sex cells of a In recent years, two accidentally introduced parasitic
plant (pollen) fertilize female sex cells of a plant (ova, or egg mites have swept through honeybee populations, decimating
cells); it is the botanical version of sexual intercourse. Plants such hives and pushing beekeepers toward financial ruin. On top of
as grasses and conifer trees achieve pollination by the wind. Mil- this, starting in 2006, entire hives inexplicably began dying
lions of minuscule pollen grains are blown long distances, and by off. In each of the last several years, up to one-third of all
chance a small number land on the female parts of other plants honeybees in the United States have vanished from what is
of their species. In contrast, the many kinds of plants that sport being called colony collapse disorder. Scientists are racing
showy flowers are typically pollinated by animals, such as hum- to discover the cause of this mysterious syndrome. Leading
mingbirds, bats, and insects (see Figure 4.8, p. 98). Flowers are, hypotheses are insecticide exposure, an unknown new para-
in fact, evolutionary adaptations that function to attract pollina- site, or a combination of stresses that weaken bees’ immune
tors. The sugary nectar and protein-rich pollen in flowers serve as systems and destroy social communication within the hive.
rewards to lure these sexual intermediaries, and the sweet smells We all can help maintain populations of pollinators by
and bright colors of flowers are signals to advertise these rewards. reducing or eliminating the use of chemical pesticides. All
Our staple grain crops are derived from grasses and are insect pollinators are vulnerable to the vast arsenal of insecti-
wind-pollinated, but many other crops depend on insects for cides we apply to crops, lawns, and gardens. When people try to
pollination. The most complete survey to date, by tropical bee control the “bad” bugs that threaten the plants they value, they
biologist Dave Roubik, documented 800 types of cultivated all too often kill the “good” insects as well. Homeowners can
plants that rely on bees and other insects for pollination. An help pollinating insects by planting gardens of flowering plants
estimated 73% of these types are pollinated by bees, 19% by and by providing nesting sites for bees. Farmers who allow
flies, 5% by wasps, 5% by beetles, and 4% by moths and but- flowering plants (such as clover) to grow around the edges of
terflies. Bats pollinate 6.5%, and birds 4%. Overall, native spe- their fields can maintain a diverse community of insects, some
cies of bees in the United States alone are estimated to provide of which will pollinate their crops.
$3 billion of pollination services each year to crop agriculture.
Populations of native pollinators have declined precipi- “Pests” and “weeds” hinder agriculture
tously, however. As one example of many, the U.S. Great Basin
states are a world center for the production of alfalfa seed, and Although pollinating insects are vital for agriculture, other
alfalfa flowers are pollinated mostly by native alkali bees that organisms weaken or destroy our crops or livestock. Through-
live in the soil as larvae. In the 1940s to 1960s, farmers began out the history of agriculture, the insects, fungi, viruses, rats,
plowing the land and increasing pesticide use in an effort to and weeds that eat or compete with our crops have taken advan-
boost yields. These measures killed vast numbers of the soil- tage of the ways we cluster food plants into agricultural fields.
dwelling bees, and alfalfa seed production plummeted. Pests pose an especially great threat to monocultures, where a
pest adapted to specialize on the crop can move easily from
Conservation of pollinators is vital plant to plant (see Figure 10.7). From the perspective of an
insect that feeds on corn, grapes, or apples, encountering a grain
Preserving the biodiversity of native pollinators is especially field, vineyard, or orchard is like discovering an endless buffet.
important today because the domesticated workhorse of What people term a pest is any organism that damages
pollination, the honeybee (Apis mellifera), is also declining. crops that are valuable to us. What we term a weed is any plant
American farmers regularly hire beekeepers to bring colonies that competes with our crops. These are subjective categories
of this introduced Old World honeybee to their fields when that we define entirely by our own economic interests. There
it is time to pollinate crops (Figure 10.17). Honeybees polli- is nothing inherently malevolent in the behavior of a pest or a
nate over 100 crops that comprise one-third of the U.S. diet, weed. These organisms are simply trying to survive and repro-
272 contributing an estimated $15 billion in services. duce, but they affect our farm productivity in doing so.

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