The problem caused by grass grub Costelytra zealandica (white) in New Zealand pastures: The need for a sustainable agriculture approach

Larvae of the soil-dwelling scarab Costelytra zealandica (White) have historically been considered as the most important insect pest in New Zealand pastures. Pasture deterioration and losses in production are primarily induced through larval injury to plant roots. In the last 25 years, control of c. zealandica larvae has mainly been based on the paradigm of the green revolution. However, in recent years this paradigm has collapsed leaving behind multiple environmental problems. Reliance on the use of pesticides and fertilizers in agriculture has increased production costs. The realization that higher production does not necessarily means higher returns has also been a driving force in the search for new strategies. Furthermore, evidence suggests that this insect may play an important role in soil organic matter (SOM) mineralization and dynamics in pastures. Results from our current research involving laboratory and field experiments suggest that by encouraging the build up of SOM, prevention and reduction of insect damage are possible. The results also suggest that efforts should be made to improve the efficiency of biological control agents introduced into soil to optimize the presence of indigenous soil biota and; to enhance the contribution that C. zealandica larvae can make to SOM turnover. Conservation and encouragement of soil fertility through SOM inputs may be crucial as a sound alternative to prevent the damage caused by C. zealandica. These measures are discussed and recommended for a healthy sustainable pastoral agriculture