resistance

There is an increasing requirement to breed durable resistances to woolly apple aphid (WAA) into apple cultivars. Genetically diverse apple plantings have been established in New Zealand with one aim to identify new sources of resistance to this pest, and also to allow the computation of parameters of genetic interest. Such computations are hindered by the uneven distribution of the pest in the orchard. The spatial distribution of WAA was investigated using local trend surfaces to examine large scale patterns, and point process analyses to check for the presence of small scale clumping.

Bonamia is a protozoan parasite of the haemocytes of oysters (Tiostrea chilensis), in which it has an annual developmental cycle between November and August each year. The parasite transmits directly, oyster to oyster, and therefore disease spread is related to host stock density. The Foveaux Strait oyster population experiences large mortalities every 20-30 years, and these may be attributable to Bonamia. The parasite appears to become less pathogenic at the end of, and probably between, mass mortalities, and some oysters appear more tolerant of infection than others.

Withdrawal of the use of cheap, persistent organochlorine insecticides in New Zealand pastures has shifted the emphasis of insect pest control to non-chemical methods during the last 10-15 years.

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.