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Endangered
Pollinators
By: J. K.
Maheshwari
The
splendour, variety and colour of flowers arises from their need for pollination
- the transference of pollen grains from the male organs, the stamens to the
female stigmatic organs or ovaries in flowers. Pollination is critical to fruit
and seed production, and is often provided by insects and other animals on the
hunt for nectar and pollen. This interdependence is primarily based upon the
ability of the flowers to supply carbohydrate-loaded nectar and protein-rich
pollen as food for the pollinators and the ability of the insects to transfer
pollen to the stigma when feeding or searching for food. For 200 million years,
insects and flowers have been closely and mutually interrelated in evolution as
reciprocal selective factors. They have evolved together to produce some
amazingly specialized and ingenious pollination mechanisms. The entomophilous
species of plants may be adapted to certain insects, e.g. figs to a wasp,
Blastophaga; Phlox to a diurnal butterfly, Hemoris; Yucca to a
tineid moth, Pronuba; red clover to bumblebees; Trollius to a
blade fly, Chiastochaeta; etc. In the case of some orchids, e.g.
Ophrys insectifera, the flowers have very striking resemblances with the
females of certain wasp species of Scolia. Male wasps visit the flowers
not for nectar or pollen, but just due to the visual simulation of flowers
resembling their females, thus pollinating them incidentally. This dramatic
relationship between plants and their pollinators is one of the most
significant events in organic evolution.
Animals and
insects provide pollination services for over three-quarters of the staple crop
plants and for 80 per cent of all flowering plants in the world. The economic
value of animal pollination to world agriculture has been estimated to be 200
billion US dollars per year. More than one lakh different animal species play
roles in pollinating the 250,000 kinds of wild flowering plants on our planet.
In addition to bees, wasps, moths, butterflies, flies and beetles, as many as
1500 species of birds and mammals serve as pollinators. Hummingbirds are the
best known wildlife pollinators in the Americas, but perching birds, flying
foxes, fruit bats, snails, slugs, possums, lemurs and even a gecko function as
effective pollinators elsewhere in the world. Many crops of commercial
importance (almond, cherry, pear, apple, coffee, sunflower, turnip rape, water
melon, cucumber, melon, avocado, alfalfa, etc.) rely on pollination by insects,
and of these insects, bees are by far the most important. The bees fall into
two categories: wild bees and domesticated honeybees. Honeybees of the genus
Apes have been cultivated by man for many centuries in various regions of
the
Old World
where they occur naturally. A main reason for the domestication of bees has
always been the production of honey and beeswax. However, the importance of
these insects for pollination has not been missed and apiculture has usually
gone hand-in-hand with agricultural production of crops requiring bee
pollination. Wild bees of hundreds of species are also important pollinators
and are more effective than the honeybees for certain crops and in colder
-climates.
The
population of both wild and managed pollinators is declining at alarming rates
owing to alteration in their food and nesting habitats, shrinkage in natural
ecosystems, i.e. forests and grassland ecosystems, pesticide poisoning,
diseases and pests, over-collecting, smuggling and trading in certain rare and
endangered species. Insects (butterflies, moths, bees, wasps, ants, beetles,
etc.) numbering about 500 species are an important supplementary source of
calories and proteins in many regions of the world. Honeybees, economically the
most important crop pollinator worldwide, are in decline. The number of
commercial U.S. bee colonies had fallen from 5.9 million in the late 1940s to
2.7 million in 1995. The loss of one quarter of all managed honeybee colonies
since 1990 signals one of the most severe declines U.S. Agriculture has ever
experienced in such a short period. An estimated 20 per cent of all losses of
honeybee colonies involve some degree of pesticide exposure. Some pesticides
highly toxic to bees and birds are: aldrin, carbaryl, carbofuran, diazinon,
dieldrin, endosulfan, EPN, fenthion, heptachlor, malathion, monocrotophos,
parathion, phosmet, etc. In a recent field study at Cornell University in the
U.S.A., it was found that monarch butterfly caterpillars eating Bt corn toxic
pollen blown on to milkweed plants near Bt corn fields had suffered significant
adverse effects leading to death of nearly 20 per cent of the caterpillars.
These chemicals and toxins can eliminate nectar sources for pollination,
destroy or adversely affect larval host plants for moths and butterflies, and
deplete nesting materials for bees. Gardeners, orchard growers, farmers and
urban dwellers can switch to more pollinator-friendly organic methods of
cultivation to reduce wildlife exposures to insecticides, herbicides and
fungicides.
There are
over 1500 species of butterflies in the Indian subcontinent, but their
population is dwindling because of the indiscriminate use of insecticides and
chemical weed-killers as well as atmospheric pollution. Many other manmade
environmental changes like deforestation, extension of farming and unrestricted
urbanization are also threatening some species of butterflies to extinction by
destruction or disturbance of their larval as well as adult food plants,
feeding grounds and shelters. The Travancore Evening Brown, the Malabar Tree
Nymph, Bhutan Glory and Kaiser-I-Hind Butterfly are listed as endangered due to
the wanton destruction of habitats in various parts of the subcontinent. Many
of the most spectacular and endangered species have various levels of
protection under CITES as well as under local legislation. However, there is a
major trade in the spectacular tropical species for incorporation in ornaments
and souvenirs. The international demand for insects is greater than most people
realize. Next to bees and moths only, butterflies are most efficient
pollinators of flowers to help turn them into food crops, fruits and seeds so
essential for the survival of man and animals. Wildlife farming, based on
sustainable exploiting wild creatures, can help to save endangered species like
butterflies and their habitats.
Over the
past decade, farmers in the Himalayan region have been complaining about
decline in apple production and quality due to pollination-related problems.
Apart from habitat alteration from highly diverse natural ecosystems far less
diverse agro-systems, indiscriminate use of pesticides, and the over-harvesting
of honey through traditional honey-hunting methods have contributed to the
extermination of both the diversity and abundance of pollinating insects. The
general observation of farmers is that, in the past, there used to be a lot of
insects such as wild bees, butterflies and moths during the apple flowering
season but now they have all disappeared. The scarcity of natural insect
pollinators has, therefore, become a critical factor in inadequate pollination.
The solution lies in supplementing populations of crop pollinators such as
honeybees, bumblebees, sting less bees, solitary bees etc. Farmers in Himachal
Pradesh are using honeybee colonies of Apis mellifera and A. cerana
for pollination. Hand pollination of apples is a common practice in Maoxian
County of Sichuan, China. Awareness about the value of honeybees as crop
pollinators has to be raised at all levels among planners, policy makers,
beekeepers or farmers. In western countries, farmers are already using
honeybees and solitary bees (species of Osmia, Megachille, Nomia, Xylocopa
etc.) for pollination of different crops. The focus of beekeeping needs to
change from conventional honey production to crop pollination.
Late
Dr. J.K.
Maheshwari was
a Fellow of the National Institute of Ecology and Retd. Scientist, National
Botanical Research Institute, Lucknow, India. |
