Insect density effects in root feeding by larvae of Sericesthis nigrolineata (Coleoptera : Scarabaeidae)

(1) Insect density effects were investigated under glasshouse and laboratory conditions for third-instar larvae of Sericesthis nigrolineata feeding on the roots of perennial ryegrass. (2) In the presence of plants there was a reduction in larval growth rate at the higher insect densities after sixteen weeks. (3) The oven-dry weight of larval gut contents was not influenced by insect density, but there was a decrease in the percentage organic matter in the foreguts and in the assimilation of organic matter from the guts with increasing insect density. (4) Larval density did not influence larval survival, depth of feeding, movement in the soil, or respiration. The density effects appeared to be caused by a shortage of suitable food which in this case was probably young living roots.