New Zealand grass grub

Systematic position: The pest belongs to the order Coleoptera and the family Scarabaeidae. The genus Costelytra, particularly the species Costelytra zealandica, is widely recognized as a significant agricultural pest, known commonly as the New Zealand grass grub due to its destructive habits in grasslands and turf.

Crops affected: This insect is a highly polyphagous pest. It primarily targets pasture grasses, causing extensive damage to dairy and sheep farming regions. However, it also attacks various annual crops, including wheat, barley, maize, potatoes, and young nursery stock, focusing its feeding activity on the subterranean plant parts.

Biology and life cycle: The life cycle is univoltine, completing within one year. Adult beetles emerge during the summer months to feed on tree and shrub foliage and to mate. Females then deposit eggs into the soil. Upon hatching, larvae progress through three instars, feeding on roots in the soil profile before pupating and completing the cycle as adults.

Nature of damage and pest status: The damage is primarily caused by larvae feeding on plant roots. This feeding activity severs the root system, preventing water and nutrient uptake. Consequently, patches of pasture die off, leading to significant yield losses, pasture degradation, and an increased risk of soil erosion due to the destruction of the vegetative cover.

Protection measures: Integrated Pest Management (IPM) is essential for effective control:

• Application of biological control agents, such as specific soil-dwelling bacteria or fungi.
• Mechanical soil cultivation to disrupt the larvae and expose them to predators.
• Strategic use of soil insecticides where chemical intervention is deemed necessary.
• Monitoring adult flight periods using light traps to time the application of preventative measures effectively.