PURSUIT OF NO. 1 PEST

Press, Volume XCIV, Issue 28050, 18 August 1956, Page 9

PURSUIT OF NO. 1 PEST

Campaign Against Cabbage Aphid RESEARCH WORKERS ACTIVE Research workers are trying to combat the cabbage aphid which does so much damage to both feed and seed crops of brassicas. This year it was responsible for spreading the virus which wiped out thousands of acres of turnips in Canterbury and Nortn Otago. While the practising farmer or gardener may be interested only in how to control the apids which ruin his turnips or brussels sprouts, the research worker aims at knowing more than this. SO as to have an intelligent grip of what goes on in the world of Nature, he needs to gain as much detailed knowledge as possible of the biology of the pest. This is the reason behind a recent trip of two members of the staff of the entomology division of the Department of Scientific and Industrial Research at Ashburton, Messrs A. D. Lowe and J C. Storrier. This trip is part ol a survey covering the whole Deminion and aims at finding out how the cabbage aphid lives in the winter. The scientific name of this aphid, by the way, is revicoryne brassicae.

Life-cycle In Europe the life-cycle of this pest has been well known for many years. The females hatch from eggs in the spring, giving birth to live females throughout spring and summer. In autumn both males and females are produced. They fly and mate and eggs are then laid. The pest then survives the winter in the egg form. Through this cycle the insect has. say Messrs Lowe and Storrier. probably been present in New Zealand as long as the white man. No thorough check has yet been made to determine whether the egg stage is present in New Zealand during that time. So far this has never been reported, but this absence of information is not positive enough to satisfy scientific standards. At present it would appear that like so many other creatures—rabbits and opossums not excepted, the insect has adapted itself to New Zealand conditions by continuing to reproduce throughout the winter, but at a reduced tempo, by what is normally considered the survival cycle. The survey made so far indicates that this is so, as very small aphids, obviously recently born, have been observed during May and June, in many parts of the South Island. Elusive Males Recent research in England unde? controlled laboratory conditions has shown that the production of male forms, and the capacity to lay eggs follow only when the female aphids have been exposed to the long days ot summer. It is possible that no part of New Zealand has a day-length sufficient to trigger this activity, but special attention will be paid to the far south of the South Island in this survey. One of the really tricky points in this study—and there are several—is that in a 20-year study of aphids and their identification conducted by Dr. W Cottier, now director of the Entomology Division at Nelson, only one male of the cabbage aphid has ever been found in New Zealand. This specimen was submitted from Stratford, near Mount Egmont, a part of the Dominion never exposed to great day-length. Such, however, is only one of the many problems of the research worker who is traditionally and necessarily very painstaking and very, very patient. However, the survey, which will continue in the South Island this winter, and which will be extended to the North Island next year, will, sav Messrs Lowe and Storrier, establish once and for all what the biological habits of this pest really are during winter in New Zealand. From this point further deductions will be possible which should greatly assist practical control under field conditions.