population regulation

Towards greener pastures—Pathogens and pasture pests

Two of New Zealand's most important insect pests, grass grub and porina, are endemic species which have successfully colonised improved pastures. Population densities of these insects within this new environment are far greater than in the native plant systems in which they evolved. Within these high populations diseases have flourished, and high numbers of diseases are recorded from each of these pests. These include bacteria, fungi, nematodes, viruses and protozoa.

Population Regulation in Insect Herbivores—Top-Down or Bottom-Up

Recent evidence points to the plant's being a much more limited resource than previously expected. In addition to the restraints on feeding and population growth imposed by such factors as leaf toughness, the physical environment, plant nutrition, etc., recent work points to the role of feeding- induced chemical changes in the leaves in reducing herbivore 'fitness'. This suggests that population regulation in herbivores may indeed sometimes be from the trophic level below that of the herbivore—the plant itself.