Saturday, June 25, 2011

Pests that cost virus to the crops


BITING AND CHEWING PESTS
Insect pests in this group have mouth parts which are specially made of biting and chewing plants. This mouth parts of insects in this group consist of a pair of very hard biting jaws called, maxillae, a flat upper lip called the labrum, and a lower lip known as the labium. The mandibles are used to bite off and chew parts of crops while the maxillae are used to push the parts of the crop into the mouth. Examples of biting and chewing insects are grasshoppers, beetles and crickets.
These insects feed on many plants such as okra, cassava, maize, cowpea, millet and vegetables. Their damage can be easily recognized by the holes which are made on the leaves or sometimes the whole leaf is eaten up where the leaves and the stems have been eaten up by grasshoppers. You can see the damage done to cassava in Nigeria by grasshoppers especially during the dry season months of November, December, January and  February. Locusts are grasshoppers which live together in very large  groups. They are  well known all over Africa as serious pests of several crops. Locusts eat everything that is green and they can eat up everything in a farm within one single day.
Another well known pest which destroys crops is called the armyworm. These are the blackish caterpillars with yellow stripes or marks which move in dense groups like an army. They eat up grain crops like maize, millet and sorghum.
Another group of biting and chewing pests are the boring insects. These pests bore holes into crops and live inside, feeding on the internal parts of the crop. The been beetle which you find on beans in the market is a good example. Other pests which bore into crops are caterpillars known as ‘stem – borers’ of millet, sugarcane, maize and sorghum.

PIERCING AND SUCKING PESTS
The second group of pests are the piercing and sucking insects. These are pests in which the mouth parts are shaped like an injection needle. With the mouth parts shaped in this way, the pests easily pierce into the stems or fruits and seeds of crops and suck juice from them.  Piercing and sucking pests damage crops in three major ways as follow:
(1)               When they pierce and suck sap from crops, they destroy the tissues of the crops and the crop plants become week and may even die. Such plants therefore do not grow well.
(2)               Crop plants which are pierced have holes through which many harmful organisms can enter the plants to cause diseases which kill the crops. Such harmful organisms are fungi, bacteria and viruses.  
(3)               Sometimes piercing and sucking insects actually transfer harmful organisms from an infected crop to a healthy one. For example aphids transfer viruses from one groundnut crop to another or from infected cassava plants to other health cassava plants.
Piercing and sucking pests also causes problems to man and to livestock. For example, mosquitoes transmit the tiny parasites which cause malaria fever. Tsetse files also transmit tiny worms to men and livestock causing the illness called sleeping sickness.

NOTABLE CROP PESTS IN NIGERIA
Insect pests are destructive in Nigeria’s agriculture. Agricultural scientists us that up to 25 percent, i.e. one quarter of all the food we produce in Nigeria is destroyed by insect pests which damage the crops both in the field and even when they have been harvested and stored for our use.
Although different kinds of insect pests attack our crops, not all of them causes serious damage; some pests are more damaging than others. The following Table describes some notable insect pests in Nigeria’s agriculture.



INSECT PEST OF SOME NIGERIAN CROPS

1.               BITING AND CHEWING PESTS

S/NO

NAME OF PEST

MAJOR CROPS DAMAGED

KIND OF DAMAGE CAUSED
(a)
Grasshoppers (Zonocerus, variegates)
Cassava, Plantain, Bananas, Vegetables, Maize Millet, Groundnuts.
Nymphs and adults eat leaves and stems.
(b)
Cowpea leaf beetle (Ootheca mutabilis)
Yams, Timber, Cowpea.
Adults make holes in the cowpea leaves.
(c)
Termites
Maize, Sorghum, Millet.
Adults eat the roots of growing plants.
(d)
Crickets
Vegetables.
Nymphs and adults eat the stems and roots of plants.
(e)
Armyworm
Maize, Rice
Caterpillars eat all the leaves of grasses (i.e. pasture).

2.         PIERCING AND SUCKING PESTS
(a)
Aphids
Groundnuts, Cowpea, Maize
Insects pierce leaves and pods and transmit virus diseases which kill plants
(b)
Thrips
Cowpea, Cocoa, Onion.
Nymphs and adults pierce leaves and flowers and cause them to wither and drop off. Thrips also transmit virus diseases to crops
(c)
Cotton Stainer
Cotton, Okra.
Pierce the leaves and fruits causing them to dry and drop off. Also transmit fungus disease.
(d)
Shield Bugs
Cocoa, Cowpea, Oranges.
Nymphs and adults pierce and suck the fruits
(e)
Mealy – bug
Cassava.
Nymphs and adults pierce and damage leaves. Also transmit virus diseases

3.                    BORING PESTS
(a)
Stem Borers
Maize, Rice, Sorghum, Millet.
Caterpillars eat into the sterms and destroy the growing tips of the plant.
(b)
Weevils
Cowpea, Rice, Yam, Potato, Groundnut.
Adults and larvae bore into the seeds of crops and damage them in the field and in the store.