Degree of plant root digestion by the larva of the beetle, Costelytra zealandica

Abstract

The degree of plant root digestion by grass grubs ( Costelytra zealandica) has been evaluated by scanning electron microscope examination of plant residues in faeces. Faecal pellets were examined from grubs fed on roots of pure plant species (perennial ryegrass, Lolium perenne, and white clover, Trifolium repens) under soil-free conditions, as well as from naturally occurring grubs on mixed pasture. There was considerable variation in the degree of digestion observed with different plant species. Clover root was more extensively digested with formation of partially digested xylem vessels, whereas ryegrass root appeared to undergo very little digestive breakdown. These results indicate that plant structural carbohydrates undergo limited digestion by the grass grub. Thus grass grubs may require a high turnover of dietary root material, which would explain the highly destructive effect of the larvae on pasture plants.