Insect density effects in root feeding by larvae of Sericesthis nigrolineata (Coleoptera: Scarabaeidae).
Abstract
In further investigations on feeding on larvae of Sericesthis nigrolineata (Boisd.), a pest of pastures in New South Wales [cf. preceding abstract, RAE/A 64, 4113, 4257], insect density effects were studied under glasshouse and laboratory conditions for third-instar larvae on the roots of perennial rye grass (Lolium perenne). In the presence of plants there was a reduction in larval growth rate at the higher insect densities after 16 weeks. 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 fore-gut and in the assimilation of organic matter from the gut with increasing insect density. Larval density did not affect 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 probably consisted of young living roots.