An investigation of the control of mite populations (Tetranychus urticae Koch) resistant to organo-phosphates

Although spider mites have been reported as pests only since the late 19th Century (Titus, 1905, seen in Leigh, 1963), they appear to have been a pest problem whenever crops have been grown since earliest human cultures. The control of spider mites, however, was not a great problem to agriculturalists until two decades ago. The pest of orchards which is the so-called European red mite or fruit tree red spider mite, Panonychus Metatetranychus) ulmi Koch (= Paratetranychus pilosus C. & F.) had been noticed in various parts of the world, in particular in England and America, during the past fifty or sixty years. From about 1920 another mite of possibly even greater economic significance developed as a pest. This is the two-spotted spider mite or the glasshouse red spider mite or red carmine mite, Tetranychus urticae Koch (= T. Telarius L., T. Bimaculatus Harvey and T. Althaeae Hanstein). The damage caused by these pests, compared with that inflicted by other plant parasites, was of secondary importance, and application of proven insecticides such as organo-phosphorus (O/P) compounds kept both spider mites and insect pests well in check till several years ago. Recently, however, the two-spotted spider mite became the most difficult to control among all the pests that confront horticulturists and agriculturalists (Naegele and Jefferson, 1964). Price, Walton and Drew (1961) reported the species as the most serious pest with which florists have to contend. Nowadays, in spite of control measures, many orchardists and ornamentalists suffer economic loss due to defoliation, reduced tree vigor, poor fruit colour, or small fruit brought on as a results of mite feeding. This state reflects the general pattern which is occurring now, and is primarily due to the development of resistance to acaricides in the mite population. The major problem in the chemical control of spider mites throughout the world is the continued development of strains resistant to the common chemical compounds used against them. Each year the problem becomes more severe with an increase in the number of resistant species and greater number of chemical types, especially organo-phosphorus compounds, to which the species are resistant Thus combating the spider mites on economic field crops in the world has proved to be a difficult task in recent years. The aims of the present research are: 1) To determine the levels of toxicity of organophosphates to populations of spider mites; 2) to investigate methods for the control of organophosphate resistant populations of spider mites; 3) to apply laboratory findings to field conditions.