WHITEFLY is highly polyphagous which feeds on 437 plants belonging to 63 families as recorded in 67 countries.

Out of these, 79 plants belong to Leguminosae, 41 to Solanaceae, 41 to Compositac, 36 to Malvaceae, 29 to Euphorbiaceae, 25 to Cucurbitaceae, 14 to Cruciferae and remaining 172 to other 56 families. In Pakistan, it is known to attack 104 plants belonging to 24 families.

Firstly, whitefly B. tabaci was described in Greece in 1889. It was partially responsible for a drastic reduction in yield of American varieties of cotton in the Punjab during 1919, 1921, 1923 and 1927. Similarly, severe outbreaks were reported from El-Salvador, India, Iran, Iraq, Israel, Sudan, turkey and now in Pakistan. In some of the countries, it also acts a vector of viral diseases, such as cotton leaf curl virus in Africa and Pakistan and of tobacco leaf curl, tobacco, yellow net virus and several other viruses affecting beans Cucurbits and other cultivated crops in India.

Any attack of whitely, not only reduces the yield but whatever lint and seed is produced, it is of poor quality. Ginning percentage, lint index, micronaire value and weight of seed is also reduced. Similarly, FAO estimated that the whitefly (Bemisia tabaci) can reduce irrigated seedcotton yield by 44 0-per cent.

Whitefly population flared up during the last 10 years in Punjab and Sindh caused severe damage in cotton growing districts. Population persisted till the end of season and no insecticide proved effective against this pest. The possible reason which may have contributed to its inadequate control, may be the intensive use of pesticide which adversely affected natural enemies resulting in higher infestation as reported in Sudan, Central America, Turkey India and other countries. The other reason for its ineffective control is the protecting covering on nymphs and pupae and the location of nymphs and pupae only on the under surfaces of leaves on the lower part of plants. It is also due to development of resistance as it happened in other parts of the world.

Studies were carried out at the Central Cotton Research Institute, Sakrand, (Sindh), for developing integrated methods for control of whitefly, and insecticidal formulations based on vegetable oils, Different oils varied in potency, speed of action and bio-persistence, in such parameters as: residual activity against adult and immature Bemisia tabaci, spray toxicity to larval stages and modification of adults behaviour expressed by settling and oviposition deterrence.

The tested materials were kerosene oil, ground nut, coconut, castor, cottonseed oil, sunflower cooking oil and detergent powder. Among these seven tested materials, groundnut, castor and cottonseed oils showed the most prominent activities. Kerosene and coconut oils were the most phytotoxic and castor oil was found safest for crop, under ideal spray conditions with complete coverage of underside of leaves. It was found that cottonseed oil gave 70 per cent reduction results on the average infestation level of whitefly,

These non-conventional insecticides usually did very little damage to natural enemies (predator and parasitoids) populations while killing high proportions of pest. Insecticides usually used in the cotton field were found to be monocrotophos and more harmful than endosulfan against natural enemies. The introduction of this study can prove a good base for any sustainable integrated pest management programme in future.

Whitefly management: To manage whiteflies, it is necessary to know which plants they affect and to understand the nature of such damage. It is also necessary to know how to monitor whitefly populations (sites, dynamics, action thresholds), besides, limitations of various control tactics which include cultural controls (such as altered planting practices and physical barriers), host plant resistance, chemical controls and natural controls.

At present, chemical control of whiteflies is both expensive and increasingly difficult. If the rate of whitefly re-infestation is great enough, cost of effective insecticide treatments may be prohibitive. Besides the cost of treatment, other factors involved in chemical control decisions, risk of secondary pest out-breaks, that of the whiteflies developing insecticide resistance have to be taken care of.

One solution for any pest problem is to prevent it through cultural manipulation of crops. control options including adjusting planting dates. Highly susceptible crops, such as cucurbits, crucifiers and tomatoes should not be planted when whitefly migration is expected. Field location also can affect potentials of whitefly infestation. The earliest and heaviest infestations, often occurs in fields located near crops with prior or current infestations. This has been observed in spring melon crops located near infested cabbage, and in summer cotton located near infested cabbage or cucurbit fields. To combat the problem transmitted viruses, all infected plants be removed. Susceptible crops should not be grown continuously because they provide an ever-increasing source of inoculum.

Host plant resistant (HPR) is one of the preferred methods for minimizing damage caused, because it does not require complete elimination of pest. The HPR protects the crop by making it less suitable and more tolerant to pest.

Such examples are: (i), use of smooth leaf (glabrous) cotton rather than hairy leaf cotton to reduce the impact of whiteflies on yield, and (ii). resistance to cotton leaf crumple virus in the Cedix cotton and resistance to CLCV in CIM-446, CIM-448 varieties.

There are five parasitoid genera of wasps that are known to parasitize the Bemisia spp. complex. Whiteflies that are parasitised by these wasps are often identified by a round emergence hole in the whitefly pupal case:

(1) Amitus (Platygasteridae, Platygasteroidea)

(2) Encarsia (Aphelinidae, Chalcidoidea)

(3) Eretomocerus (Aphelinidae, Chalcidojdea)

(4) Signiphora (Siguiphoridae, Chalcidoidea)

(5) Metaphycus (Encyrtidae, Chalcidoidea)

Encarisia and Eretmocerus are the two main parasitoid genera attacking Bemisia species.