Side-effects of pesticides on the life cycle of the mite pathogenic fungus Neozygites floridana

Abstract

The tomato red spider mite, Tetranychus evansi Baker and Pritchard, is an invasive species in Africa causing considerable damage to Solanaceous crops. The fungal pathogen Neozygites floridana Weiser and Muma from Brazil has been considered a potential candidate for introduction into Africa for the control of T. evansi. To be incorporated in the tomato production system, N. floridana has to be compatible with the pesticides used for the control of other pests and diseases. Pesticides used in tomatoes that might affect the fungus were therefore studied by the use of different methods. Two insecticides (Lambda-cyhalothrin and Methomyl), two acaricides (Propargite and Abamectin), and two fungicides (Captan and Mancozeb) were tested in two concentrations: the mean commercial rate (CR) and 50% of the mean commercial rate (CR/2). Fungus-killed mite cadavers or the substrates used for sporulation (leaf discs and coverslips) were either immersed or sprayed with the pesticides before testing their effects on sporulation, germination of primary conidia and infectivity of N. floridana. Direct immersion of cadavers, coverslips or leaf discs into pesticides affected sporulation and germination stronger than the spray tower method, although infectivity of capilliconidia was neither affected by the method of application nor the concentration of the pesticides. The fungicides Captan and Mancozeb resulted in a high reduction in sporulation and germination at both concentrations. Propargite did not inhibit sporulation but affected germination of primary conidia. Methomyl and Abamectin resulted in less effects on N. floridana.