1. Brown Wheat Mite
Petrobia lateens (Muller) (Arachnida: Tetranychidae)
Distribution: It occurs on wheat in the summer rainfall regions and expected to be severe where drought conditions are frequently encountered.
Nature of damage: The brown wheat mite feeds on sap from leaves by inserting two needle-like stylets into the leaf thereby withdrawing nutrients from the plant. During high mite populations the leaves may have a bronze appearance with some leaves even dying off as a result of intense feeding. They have a tendency to feed on the tips of the leaves, causing them to dry out and die. Heavily infested fields present a scorched withered appearance. Showers of 12mm or more may lead to the eradication of the mite population, but eggs present in the soil may start a new generation.
Life history: The mites are very small measuring about 0.5 mm in length, metallic brown to black with pale yellow legs and their forelegs are distinctively longer than the other three pair of legs. Eggs are generally laid beneath clods and are either active i.e. red in colour and not visible to the naked eye or dormant i.e. white eggs
clearly visible on the underside of clods. Under favourable environmental conditions eggs hatch within 9 – 11 days. Dormant eggs may remain in the soil for long periods and hatch during July/August following light rainfalls. Dry conditions favour larval development and adulthood can be attained within 8 – 11 days. Only females occur and eggs are laid within 2 days after reaching adulthood. Subsequently, mite populations often reach pest status under dry conditions. The total life cycle is completed in 25.5 days.
Management strategies:
(i) Spraying formothion or oxydemeton methyl or phosphomidon @ 250 g a.i./ha. Spraying may be repeated after 15 days in case of severe infestation.
(ii) Growing of tolerant wheat variety such as C-306.
2. Grain aphid Sitobion avenae (F.) (Aphididae : Homoptera)
Distribution: This pest is found distributed worldwide in parts of Europe, Asia, Africa, North America, Central America and Caribbean and South America. In India it is reported from Delhi, Haryana, Himachal Pradesh, Jammu and Kashmir, Madhya Pradesh, Punjab, Rajasthan, Uttar Pradesh and West Bengal.
Nature of damage: A major pest of cereal crops in the spring. Heavy infestations can cause a reduction of the number of grains per ear and thus a noticeable reduction of the yield. Sooty moulds develop on the honeydew which they secrete. This aphid is also a vector of the barley yellow dwarf virus (BYDV).
Life history: Primary hosts of this aphid belong to the genus Pubus. Secondary hosts mostly belong to the Poaceae (=Gramineae), including grasses like cocksfoot grass, and also cereals viz., oats, wheat, rye, barley. Winter eggs are laid on the straw of graminaceous plants and hatch in late winter, giving rise to several generations of apterous, virginoparous fundatrigeniae. Winged aphids emerge, spreading to other graminaceous plants and developing on the uppermost leaves before moving to ears as soon as these emerge. When populations are abundant or when the ripening grain hardens, winged aphids appear in a few days, leaving to create new colonies on Poaceae which are still green. During mild winters, this species survives parthenogenetically on new growth of winter cereals and other Poaceae.
Management strategies:
(i) Spraying formothion or oxydemeton methyl or phosphamidon @ 250ml a.i./ha.
(ii) Growing aphid resistant barley varieties DL117 or DL200.
(iii) Early sowing of barley by 1st fortnight of November usually reduces aphid attack.
3. Shootfly Atherigona naqvii (Muscidae: Diptera)
Distribution: Occurs in all wheat growing areas.
Nature of damage: The maggots bore into the shoot of young plants, a week after germination to about one month and as a result the central shoot dries up resulting in ‘dead hearts’. If it is a little later the mother plant may produce side tillers. But the tillers also may be attacked. The infestation often goes as high as 60%.
Life history: The adult is a small dark fly. It deposits whitish eggs singly on the central surface of the leaves. The eggs hatch in 1 – 3 days and the maggots which are yellow in colour migrate to the dorsal surface of the leaf, enter the space between the leaf sheath and the axis and make a clean cut at the base of the leaf. The growing
point of the plant dies and decays on which the maggots feed. The larval period lasts for 6 – 10 days. Pupation takes place inside the stem itself and the adults emerge in about a week. Each female fly is capable of laying 30 eggs during its life time. Life cycle occupies 17 – 20 days.
Management strategies:
(i). Early sowing of wheat will reduce the attack.
(ii). In late sown crops (end of December to 1st week of January) spraying of cypermethrin 0.002% twice at fortnightly intervals in seedling stage was found effective. The most vulnerable period of crop is being upto 60 days of germination.
