Insect pests are a major problem for New Zealand’s primary industries, causing millions of dollars worth of lost production each year. A number of native insects have adapted to pasture plants and some horticultural crops to become significant pests.
In the 1930s ryegrass and white clover became the basis of New Zealand’s pastures. The root-feeding larvae of one endemic insect, the grass grub (Costelytra zealandica), adapted well to the new pasture from its original habitat in native tussock grasslands. It is now estimated to infest 9 million hectares of pasture land throughout New Zealand, and costs farmers in the dairy, sheep and beef industries between $41 million and $90 million annually in lost production.
Adult beetles are shiny golden to dark brown, and about 10 millimetres in length. They fly at dusk during October and November to feed on a range of trees. The beetles lay their eggs in soil, usually close to where they first emerged. Larvae feed on the roots of white clover and ryegrass, causing severe damage in autumn, particularly to pasture that is up to three or four years old.
Porina (Wiseana spp.) are also endemic insects that have adapted to pasture. Six species have been identified, the most common of which are Wiseana cervinata and W. umbraculata. Porina is a major pest in the central and southern North Island and throughout the South Island. Adult moths are light to dark brown, with a hairy body. They are short-lived, flying between spring and autumn depending on the species, with female moths releasing their eggs as they fly. They are strongly attracted to light. The grey-green caterpillars initially live on the soil surface, but after about six weeks tunnel underground. They live in these burrows, emerging at night to graze on foliage. After eight or nine months they reach their full size of up to 70 millimetres in length.
An endemic scarab, the mānuka beetle (Pyronota spp.) inhabits hill country and farmland near bush margins. The small, bright-green adult beetles feed on mānuka and other native species, while the larvae resemble small grass grubs and eat roots of various pasture plants.
The pasture mealybug (Balanococcus poae) is an endemic species that sucks the sap from the roots of grasses. It has been identified in several regions including Canterbury, Hawke’s Bay, Marlborough and the Manawatū. These small, pink, oval-shaped insects are largely sedentary and surround themselves with tufts of white wax, which help protect them in the soil.