A preliminary study of gull (Laridae) predation and cultivation effects on a grass grub (Costelytra Zealandia (white)) population in Canterbury: A thesis submitted in partial fulfilment of the requirement for the degree of Bachelor of Agricultural Science with Honours in the University of Canterbury

Abstract

The grass grub Costelytra zealandica, (White, 1846) is universally accepted as being New Zealand's most serious pest of grasslands. Until recently, however, very little attention has been devoted to its natural enemies and the role they play in the regulation and control of its populations. This apparent anomaly can in part be attributed to the cheap and efficient control obtained with DDT over the last two decades, during whieh period, most if not all, investigations into' the ecology of C.zealandica were temporarily shelved. Following the recent withdrawal or DDT from agricultural use, at a time when no comparable substitute was available, or even forseeable, considerable attention has been placed on the ecology and control of grass grub. East's (1972) thesis on starling predation of grass grub in Canterbury was probably the first major contribution to an understanding of the vertebrate predators of C. zealandica and more recently this theme has been developed by other workers such as Campbell (1973). Although East's work was primarily concerned with starlings, he also studied in a preliminary way the effects of gull predation and mechanical injury on a grass grub population at Weka Pass during June, 1970. The present study was an extension of this work. The objectives of this study were: 1) To assess the significance of gull predation on grass grub larvae in an area of infested pasture undergoing cultivation. 2) To assess the influence of cultivation on a grass grub population.