Flight behaviour of the porina moth (Wiseana cervinata)

Abstract

The importance of agriculture in New Zealand is well documented. Among the worst pests of improved grasslands are species of Wiseana, an indigenous genus which attacks pasture over a wide area of New Zealand. These insects are commonly referred to as porina, irrespective of the species involved. Large areas in the South Island and some in the south of the North Island have at times suffered porina depredation. The economic injury caused by porina is the result of pasture damage from larval feeding in the late summer and autumn. In Canterbury this damage is usually caused from January to April. Spring damage can sometimes occur from Canterbury to Southland.

The growing larvae emerge at night from near-vertical subterranean tunnels and eat the vegetation within reach. The roots die from continuous and severe defoliation. There is the possibility of permanent pasture destruction and ingress of weeds. Ten to twelve per square foot are sufficient to completely defoliate a ryegrass-white clover pasture by the end of April. Porina larvae also damage lucerne. They defoliate the crown and destroy the young shoots during winter. Stands are rarely killed, but may be slightly thinned and sometimes establishing stands are damaged. The damage is particularly severe on pastures in Canterbury, especially those on lighter soils and on areas which have been closed from grazing for hay or small seed production, in the previous summer. During the period from February to April, the larvae show a very rapid increase in size, and thus a proportional increase in the amount of grass consumed, is evident. The pasture may be bared by May or it may not be seriously depleted until August. In either case, the pasture is not able to provide the increased grass production needed for feeding young stock in the spring. Thus, the end results of porina damage are lowered production and loss of income to the farmer.

From time to time, farmers have publicised the effectiveness of lights in attracting porina moths. It was with this in mind that this investigation was carried out. The general aim of the investigation was to determine the efficacy of light traps for the control of Wiseana cervinata populations in Canterbury. In addition, it was considered desirable to investigate the behaviour of porina adults and the factors affecting it. The investigations were intended to cover the following aspects: (1) To examine the influence of climatic factors on emergence and flight. (2) To examine the influence of light traps on the flight of W. cervinata and on the number of eggs laid. (3) To find the most efficient attractant light source.