Bionomics and control of the sugarcane insect Numicia viridis Muir (Homoptera: Tropiduchidae)

Abstract

Numicia viridis Muir (Homoptera : Tropiduchidae) is an indigenous southern African insect which was 'described in 1931 from specimens collected in Pondoland and Natal. In 1962 it became of economic importance when it was associated with damage caused to sugarcane in both Swaziland and South Africa. Affected cane turned yellow, its leaves dried off prematurely, and an abnormally large amount of trash was produced. was affected. Growth was retarded, and in extreme cases stem texture Since 1962 the insect's association with both sugarcane and alternate host plants has been investigated, and its economic importance assessed. Insectary investigations included studies of life history, developmental stages and behaviour of N. viridis and of its parasites. Two Mirid egg predators (Tytthus mundulus(Breddin)and T. parviceps (Reuter) ) were introduced from Mauritius, but neither became successfully established. Field studies included general ecology, population dynamics, movement, distribution and the development of infestations. The association of N. viridis with 12 sugarcane varieties and with grass communities formed the subject of seven field experiments. All locally grown cane varieties and most grass species could serve as host plants, but differences in egg mortality rates for different host plants were noted. Natural controlling factors were recognised, including biological agents. Of these, two useful egg parasites (Ootetrastichus ?beatus Perkins (Eulophidae) and Oligosita sp. nov. (Trichogrammatidae) were the most important. Attention was given also to chemical control, and it was found that of ten insecticides tested in large scale field experiments, dust and low volume formulations of endosulfan and mercaptothion gave very satisfactory control.