The ecology of Micromus tasmaniae (Walker)

Abstract

New Zealand relies upon primary produce for ninety percent of the national income. As our farming becomes more intensive insect pests (such as aphids and grass grubs) will cause greater losses to production. The aphids introduce viruses into the plants when they feed. The green peach aphid, Myzus persicae, is a vector for sixty viruses including: lettuce big vein, lettuce mosaic, tomato spotted wilt, but it is the yellow dwarf virus carried by Rapidosiphum padi which is causing the most serious production losses in cereals. In contrast to the destruction of crops by Pieris rapae (white butterfly) and Persectania aversa (army worm), the symptoms of the virus may not be immediately obvious. Virus particles multiply in the host plants and any sap sucking insect feeding upon it may become a virus vector. The rate of aphid reproduction is determined largely by temperature and in summer a nymph may mature and reproduce five days after being born. Each individual aphid deposits not less than twenty to twenty-five progeny in each generation. If effective biological control is absent this increase is more or less unhindered and a virus may spread rapidly through a crop. Both alate and apterous aphids are virus vectors. Resistant cereal strains exist but are frequently low producers, and so chemical sprays are applied to the more susceptible higher producing varieties. Biological control of aphids by the release of predators has not yet been attempted. The following table shows how the virus (especially yellow dwarf) and weather have affected wheat production in the last three years. Although the acreage sown has been increased, production has not improved due to the detrimental effects of bad weather and virus infection. In 1963-4 production was: increased as weather and aphids were not a problem. [Table] This Thesis is a study of one aphid predator which has possibilities as a biological control agent. The original aim of this thesis was to study the life history of Micromus tasmaniae, concentrating upon the morphology. Work began in February, 1962 but ceased in May, 1962, after some preliminary reading and observations had been made. The study was resumed in January, 1964 and experimental work ceased one year later. During the latter period the theme of the thesis changed to ecology. Two areas which were studied in detail (a chou moellier fodder crop at Lower Styx and a cabbage plot in a home garden) introduced the author to the aphid problem of New Zealand.