Wheat (Triticum aestivum L.) is a major crop with largest area under cultivation in Pakistan and plays a significant role in economic stability of the country . Low yield of wheat per hectare in Pakistan compared to the other advanced countries is due to several abiotic and biotic factors, such as traditional methods of cultivation, varieties, lack of irrigation facilities, barani areas, soil fertility and incidence of insect pests and diseases. Although many insect pests attack wheat (Triticum aestivum L.) in Pakistan, severe damage is caused by aphids. Aphids cause yield losses either directly (35-40%) by sucking the sap of the plants or indirectly (20-80%) by transmitting viral and fungal diseases . Population density of aphids also depends on the abiotic factors [3-5]. During spring season (February-March) aphid population increases, at the same time biocontrol agents like coccinellids also increase as natural check on this pest.
Aphids are nearly transparent, soft-bodied sucking insects . When present in sufficient numbers, aphids can cause yellowing and premature death of leaves. They exude drops of sugary liquid known as “honeydew”, which may cause tiny scorch marks on the foliage.
Aphids are important and widespread pests on cereal crops. When feeding in sufficient numbers, they can cause significant damage. In addition, the species listed above may act as vectors of barley yellow dwarf virus.
Its scienrtific name is Oulema melanopa . Adult beetles are 4-5 mm long, have a black head, light brown thorax, and a shiny blue-green wing cover with parallel lines of small dots . Larvae are a dull to bright yellow color, but soon take on the appearance of a slimy, globular, black mass due to the mound of fecal material they produce and accumulate on their backs . The most prominent symptom of cereal leaf beetle infestations is the distinct, longitudinal stripes on leaves these stripes are produced the feeding of adult beetles and of larvae. Significant yield losses can occur in winter wheat and fall-sown spring wheat.
Its scientific name is Mayetiola destructor. Hessian flies result in stunting of the plants, thin stands, lodging, and reduced yield. Injury is caused entirely by the larvae, which suck juices from plant tissues . If infestation occurs during jointing, infested stems often will break prior to maturity. The Hessian fly is 3-4 mm long, has a black head and thorax, and a pinkish or yellow-brown abdomen. This is one of the most destructive insect pests on cereals. The Hessian fly is mainly a pest of wheat, but it may attack barley, rye, and other grasses. This pest has been reported in most wheat-growing areas of the world.
When young tillers are attacked in the fall or early spring, the tillers usually die; infested plants show the “white head” condition typically produced by stem-boring insects. The adult flies are about 6 mm in length, and pale green to yellow with dark stripes. In infested fields, 10-15% of plants may be injured. Damage can be severe in some years, but the insect seldom causes widespread damage. However, heavy infestations of individual wheat stands may kill a significant portion of the tillers. Wheat stem maggot larvae overwinter in cereal plants or grasses.
Its scientific name is Cephus cinctus. Damage by sawflies includes premature yellowing of the head and shrivelling of the grain. The larvae girdle the stem and, later in the crop cycle, lodging is common. Sawflies produce one generation per year. The larvae overwinter in the straw in the spring they pupate. Adult sawflies are small, fly-like wasps and appear from late spring to midsummer. The females deposit small white eggs in the upper nodes of stems just below the heads.
Sawfly can cause significant damage in some years, but infestations are usually discontinuous. Nearly all cultivated cereals and native grasses act as hosts, although wheat is preferred.
Adult mites are usually less than 1 mm long, and most of the plant-inhabiting species have sucking mouth parts. Mites are not insects. Adults typically possess four pairs of legs (83), while larvae have only three pairs.
Some species may produce webs and/or may cause infested plants to be severely stunted, to head poorly, and to turn white. Individual mites are so small they they can scarcely be seen with the unaided eye.
White grubs can partially or completely sever the roots of the host plants. The dying of wheat plants are thwe main symptoms.
When fully grown, the largest of these larvae may be several centimeters long and nearly one centimeter thick. White grubs are the larvae of May or June beetles. Eggs are deposited in the soil and the hatched larvae feed on roots. The duration of the larval stage varies from species to species. When the roots are not completely destroyed, the plants may survive, but are stunted and fail to produce heads. However, the distribution and extent of attack is not uniform.
Wireworm damage is very similar to that caused by other soil-inhabiting chewing insects . They have three pairs of legs , and their color may vary from a rich cream to shades of brown. Wireworm larvae may attack wheat as soon as the crop is seeded, eating the endosperm of the kernels and leaving only the seed coat. A common sign of woreworm attack is the wilting and/or dying of a number of adjacent plants, either in a row or patch. The stems of affected seedlings will be chewed just above the seed. (Wireworms are the larvae of click beetles) . The adult beetles lay eggs in the soil, usually in the spring, and the larvae may take several years to develop prior to pupating