herbivores

We quantified brushtail possum (Trichosurus vulpecula) diet in a mixed Nothofagus fusca-N. menziesii forest in north Westland. Diet comprised 49 food items of which four (Aristotelia serrata, Muehlenbeckia australis and Weinmannia racemosa foliage, and W. racemosa flowers) contributed 68%. The canopy dominant Nothofagus species were a minor diet component (<1%), while wood, fungi and bark were a small but consistent part of diet (10.1%).

This study examined whether two species of lepidopteran larvae (Cleora scriptaria and Epiphyas postvittana) were deterred from feeding on the leaves of kawakawa (Macropiper excelsum) after the leaves had been damaged in three different ways: by larval feeding, using a hole punch or a metal rasp. A hierarchy of choice experiments was performed in the laboratory, examining the feeding 'preference' of these insects between undamaged or previously damaged tissue within the same leaf, between different leaves and between different plants.

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.

Biological invasions have significantly affected New Zealand’s native species and ecosystems. Most prominent are the effects of exotic mammals and plants, whereas few invertebrate invasions are known to have major effects on native ecosystems. Exceptions are the well-known cases of Vespula wasps in Nothofagus forest ecosystems and Eriococcus scale insects in Leptospermum shrublands. This limited impact is surprising because over 2000 exotic invertebrates have become established in New Zealand, among them many pests of exotic crop plants.