SYMPTOMS: Grass grubs attack the roots of most pasture plants, but their numbers are highest under susceptible species such as white clover and ryegrass and very low under the resistant lucerne and Lotus major. Tall fescue supports relatively high populations of grass grub but with little effect on plant production.
INSECT APPEARANCE: The larvae are C-shaped when relaxed, creamy white in colour, and have a light tan head and a horseshoe-shaped cluster of anal bristles. They moult (cast their skins) three times. Newly hatched larvae are about 5 mm long and weigh only 2-3 mg.
LIFE CYCLE: Most grass grubs hatch in December and January and pupate 9-10 months later. They are found up to 150 mm below the soil surface. The first larval stage lasts about 3 weeks and the second about 6 weeks. The third instar is present until the following September or October, but completes its growth and stops feeding about July, depending on the conditions. The pupal stage lasts 3-4 weeks.