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Acaricidal field experiments were carried out and the results compared with simultaneously conducted laboratory experiments on the same mite strains. Two tetranychid mite species occurring on Egyptian cotton, Tetranychus arabicus Attiah and T. cucurbitacearum Sayed, were investigated. Population counts on the experimental sites over the 1969–70 seasons demonstrated that at the northern sites of Behera (western Delta) and Dakahlia (eastern Delta) the red species T. cucurbitacearum was dominant, whereas in the south, the green species T. arabicus prevailed. Significant differences between treatments in field experiments corresponded to differences in LC50 of ca. 7 × in the laboratory experiments using the slide-dip technique. Under conditions of high resistance towards OP and chlorinated hydrocarbon acaricides, chlordimeform was the most effective acaricide.

It has not been possible to demonstrate an increase in oviposition rate in Tetranychus urticae Koch and T. telarius (L.) owing to DDT treatment. Treatments included direct application, holding on treated bean leaves, rearing on bean plants inserted in water containing DDT or combinations of such treatments. It was not possible to confirm a report that daughters of treated mites produced more eggs than did the parent females. A definite harmful effect is evidenced by early mortality, lowered oviposition rate, and restlessness. The harmful effect is intensified by high temperature.

Tetranychus urticae Koeh and T. telarius (L.) exhibit a decided tendency to disperse from crowded colonies. If dense colonies are confined, longevity and oviposition by adults are reduced, and young have less success in maturing. Crowding does not affect hatchability of eggs. Treatment with DDT does not enhance dispersion except at high levels of dosage, and the high levels are toxic, especially to emhryonated eggs and larvae. Emulsified DDT is more toxic than DDT in wettable powder suspension. It is postulated that the outbreaks of spider mites resulting from DDT treatment of crops are the result mainly of: DDT causing dispersion indirectly through the removal of natural enemies, which in turn allows dense local populations to develop. This results in dispersion as a result of crowding, and with dispersion to predator-free surfaces, there follows an increase in the population to economically harmful levels. The terminology used for the species of Tetranychus follows that of Boudreaux and Dosse (1963).

Oil sprays as well as fumigation with hydrocyanic gas have long been used as the common means of control against scale insects on different species of citrus trees in Egypt. Applications are usually carried out late fall and winter. During the last few years some phosphorus compounds applied in summer were used for the same reason. Meanwhile it was noticed that infestation with citrus mites, especial­ly the flat mite Brevipalpus californicus, has recently increased, a matter causing many shipments of citrus fruits to be rejected for export due to the infestation sym­ptoms. Phosphorus compounds have been reported as a cause of an increase in te­tranychid mites and of populations of aphid and white flies. The following experi­ment was undertaken to investigate the effort of some phosphorus compounds, in­cluding those recommended, against citrus scale insects, on the flat mite popula­tion in comparison with certain acaricides known. to be effective against this mite.

Mites are among the most important pests affecting the citrus industry. Not only do they affect the quantity and the size of produced fruits, but they also reduce their quality due to the symptoms they cause. The citrus flat mite Brevipalpus californicus is one of the most injurious mites infesting all citrus species cultivated in both Lower and Upper Egypt. Studying the biology of that mite is no doubt an essential step towards achieving successful control.