A study on the biology and economic importance of the Argentine stem weevil, Hyperodes bonariensis kuschel, in New Zealand

Since the advent of European settlement in New Zealand, grassland farmng has dominated the landscape. Over the past one hundred years, New Zealand's development has been largely dependent on the export of pastoral products, meat, wool, butter, cheese and other animal products. All are derived from a farming system almost wholly dependent on pasture production. In 1959, income from the export of pastural products represented 90 per cent of New Zealand's export earnings. Any factors which in some way either directly or indirectly, jeopardize maximum pastoral productivity, are important to the economy and welfare of New Zealand. Several factors do restrict productivity from New Zealand's grasslands and of these insects are often important. Two species, the grass grub; Costelytra zealandica White and and the subterranean grass caterpillar; Oxycanus cervinata Walker, are recognized as being major insect pests and cause widespread damage to pastures each year. From brief reports and papers published in the last three years, it would appear that another insect, the Argentine stem weevil, Hyperodes bonariensis Kuschel, is present which could be a major pest in New Zealand's grasslands. The Argentine stem weevil is a South American beetle, only recorded in New Zealand outside of its country of origin, and is only known as a pest in New Zealand. It was first recognized as a pest of cereals and although it had been found damaging a variety of grasses, its depredations in pastures were thought to be minor and not as severe as its damage on wheat and barley. Recently it has been recorded causing damage to pastures throughout New Zealand, particularly in pastures which have a predominant grass component of short rotation ryegrass, Lolium multiflorum x L. perenne, or Italian ryegrass, Lollum multiflorum. Little work has been done on either the biology of the weevil, its control, or on the susceptibility to the weevil of various graminaceous plants of agricultural importance. The primary aim of this investigation has been to study the bionomics and the importance of H. bonariensis on selected grasses and cereals in New Zealand. It was intended to study the following aspects; (1) The life cycle of the weevil in the field. (2) Populations of eggs, larvae, pupae and adults in short rotation ryegrass pasture and Aotea wheat. (3) The behaviour of the weevil, particularly regards feeding and oviposition, flight and host plant preferences. (4) Damage to pastures and wheat crops and especially the determination of the level of infestation in the season under review. (5) The longevity of adult weevils in harvested ryegrass seed.