Ecology and Management of the Leafhopper Vectors (Cicadulina Spp.) of Maize Streak Virus

Several Cicadulina species are important pests of maize by virtue of their role as vectors of maize streak virus (MSV). Tnis study deals with various aspects of the vector/virus/host plant relationship. Developmental times for all life stages of both C. anestae and C. mbila were inversely related to temperature, and the data were used to develop a degree-day (DD) model that can be used to estimate population growth in the field. The rate of development peaked at 30 °c for both species. The seasonal abundance of C. anestae and C. mbila adults at two localities were monitored by means of sticky traps. Seasonal fluctuations in leafhopper numbers were related mainly to temperature (expressed as DD). Although C. anestae was added to the list of MSV vectors it was not an exceptionally efficient vector compared with C· mbila. MSV transmission efficiency of female leafhoppers was significantly higher that that of males. MSV incubation in maize was inversely related to post-inoculation temperature. Rapidity of MSV symptom appearance and symptom severity in maize were dependent on the number of leafhoppers feeding on the plants. Host plant resistance in conjunction with chemical control measures was shown to offer an economical solution to the problem of maize streak disease. Maize hybrids presently grown in South Africa showed varying degrees of resistance to MSV. MSV occurred more severely in white than in yellow maize. Feeding threshold period for MSV transmission by C. mbila was 30 min. The number of plants developing MSV symptoms increased progressively and disease syrnptans appeared sooner after inoculation as the feeding time was extended beyond 30 min. Corrective post-emergence sprays of contact and systemic insecticides were inefficient for the control of the maize leafhopper, C. mbila. Protection of maize against MSV infection could only be achieved effectively through pre-emergence preventative treatment with systemic insecticides applied in the planting furrow. The use of a broad-spectrum soil systemic insecticide for leafhopper control would eliminate additional insecticide applications for control of other maize pests such as stalk borers, thereby reducing cost of protection against MSV infection indirectly.