Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Causes of grass grub (Costelytra zealandica (White)) population collapse in the northern North Island of New Zealand.

Abstract

Studies of populations of Costelytra zealandica of different status (increasing or declining) in pastures in New Zealand confirmed earlier findings that high summer mortality was associated with natural population collapses, which occur frequently in northern North Island. Laboratory studies produced no evidence to implicate changes in food quality as a major cause. Screening for pathogens showed a higher level of infection in mid-summer with protozoan pathogens (mainly Nosema costelytrae and Mattesia sp.) and bacterial milky disease (caused by Bacillus sp.) in declining populations (average 41%) than in increasing ones (13%). It was concluded that these pathogens are a major cause of population collapse. Milky disease acting alone caused a spectacular decline in one population.