CHAPTER 4 - HEALTH Lisa Berndt (Scion), Margaret Dick (Scion), Denis Hocking (NZFFA), Tara Murray (Scion), Ian Nicholas (Scion), Dean Satchell (NZFFA) Of the 240 eucalypt species in New Zealand with Paropsis charybdis and Cardiaspina some individual species are more prone to fiscella. health problems than others, either insect attack or fungal. Siting can also influence the Eucalypt species do vary in their susceptibility likelihood of some health issues. This makes to pests. Many recent insect arrivals have species and site selection important factors attacked E. botryoides in particular and also in the health of eucalypt plantations. Insect E. saligna, but have not caused much damage attack is a natural part of the eucalypt forest to other species. There are currently no serious in Australia, something the trees have evolved insect pest problems with stringybark eucalypts to cope with, so ecological balance is or most of the ash group. This may be partly maintained. Some minor insect attack is fortuitous, but if some eucalypt species are therefore acceptable within a plantation, but more attractive than others, this should be a not when major parts of the crown are lost. major factor to consider during species selection, ranking equally with growth rate, Because of our proximity to Australia, we can tree form and wood properties. expect new health problems to arrive. To maintain healthy plantations, the best Some groups of eucalypts are healthier than strategy is to select more insect-resistant others. Most eucalypt taxonomists agree that groups of species, planted on the right site. the genus can be divided into seven or eight subgenera. The two major ones are the Symphyomyrtus, the Monocalyptus (or Eucalyptus) subgenera. The Corymbia Insects subgenus has now been separated out as a Any farm forester who has grown eucalypts separate genus, but for our purposes can still is probably aware of their susceptibility to be regarded as a "eucalypt". Symphyomyrtus insect pests. Some of these are now well is the largest subgenus, containing more than established in this country - many more exist 500 of the 800 recognised eucalypt species. across the Tasman Sea and may enter New Many of these are obscure and consist of small Zealand at any time. Commentators have trees found in isolated corners of Western suggested that the eucalypts are not an Australia. Others are timber and fibre species appropriate genus for forestry purposes in e.g., E. nitens, E. globulus and E. saligna, or this country because there is a seemingly common farm and ornamental trees e.g., endless supply of pests located a relatively E. viminalis, E. ovata, E. leucoxylon, E. cinerea short distance up-wind. (silver dollar). Most of the eucalypts used internationally in plantation forestry are Even when apparently good biological control Symphyomyrtus species and this has given systems have been put in place, the arrival rise to the unsupported view that only of hyper-parasites (parasites of the controlling Symphyomyrtus species are suitable for organisms) can upset the balance and plantation forestry. counteract their effect. This has happened Visit www.nzffa.org.nz for the most up-to-date information available. 49 The second-largest subgenus is Monocalyptus monocalypts, whereas numerous examples (or Eucalyptus), referred to herecan be foundas that only attack Symphyomyrtus “monocalypts”. This subgenus contains some species. 135 species including the ashes, the stringybarks, and the true peppermints. The To summarise, Symphyomyrtus species seem subgenus Corymbia includes about 113to be more susceptible to insect attack. Some, species, many from tropical areas, the best- including E. botryoides, E. camaldulensis, known locally being C. ficifolia and C. maculata. E. viminalis, E. grandis and E. globulus appear to attract large numbers of insect pests. Three The monocalypts are considered to be the of these species represent the bulk of the most highly evolved group. They retain fewer world's plantation eucalypt resource. E. nitens of the features of their eucalypt rain forest also seems to be a popular insect target. predecessor(s). Many of the features separating subgenera relate to the flowers Nothocalyptus, with its single species and other reproductive structures, but E. microcorys, is a subgenus that appears to differences in natural plant chemicals that be relatively unattractive to insects. occur in the leaves and elsewhere are also Most entomologists are aware of the possibility recognised. These chemical differences are of a relationship between subgenus and probably important in influencing insect vulnerability to insect attack, but taxonomic preference which seems to favour groupings do not seem to have been included Symphyomyrtus species. as risk factors during selection of species for A quick survey of accessible literature suggests plantation forestry. In the meantime, the a 10:1 preference for Symphyomyrtus species planting of stringybark and ash eucalypts in as hosts for 50 common insect pests in south preference to Symphyomyrtus species may eastern Australia. The larger numbers of reduce the risk of serious damage from insect Symphyomyrtus species found in that area attack. do not account for the imbalance. Some Although monocalypts may be less vulnerable Symphyomyrtus species are attacked by nearly to insect attack than other eucalypt subgenera, every eucalypt pest. Notable in this group are they are more likely to be damaged by soil- E. saligna, E. botryoides, E. viminalisborne ,fungal pathogens, especially E. camaldulensis and other closely-related Phytophthora species, when grown on wetter species. Even possums seem to show a distinct sites and in heavier soils. The ashes and preference for Symphyomyrtus eucalypts. stringybarks are known to perform better on The monocalypt species are not free from free-draining sites. attack. Some quite serious monocalypt pests Almost all the monocalypt eucalypts have exist in Australia and the commercially blond or brown-coloured timber. None of the important E. regnans, E. obliqua and E. pilularis red-coloured timbers that seem to appeal to are frequently mentioned as insect hosts in Kiwi taste are found among the species the literature. This may reflect more intense currently established in New Zealand. Red observation of forestry species. Monocalypt timber is found mainly in Symphyomyrtus insect pests in New Zealand include the species, the best known being E. saligna and blackbutt leafminer (Acrocercops laciniella) E. botryoides. Two monocalypts with red which also attacks Symphyomyrtus eucalypts, timber are well known in Western Australia. and a number of other insects that do not These are E. marginata (jarrah), which has discriminate between species, e.g. leafrollers. never thrived in New Zealand, and E. jacksonii Some Symphyomyrtus pests also attack(red tingle). The latter has highly-regarded monocalypts. The emperor gum moth timber but its natural occurrence is very (Opodipthera eucalypti) is found on ash or restricted. With more trial, error and research, stringybark eucalypts, where it rarely causes this might be a red timber species for New major damage. On the other hand it can totally Zealand in the future. At this stage little is defoliate small Symphyomyrtus trees. Very known about its vulnerability to pests and few, if any, insect pests are restricted to diseases. 50 Visit www.nzffa.org.nz for the most up-to-date information available. P. charybdis on eucalpt foliage with typical scalloped leaf edges Eucalyptus Tortoise Beetle (P. charybdis) P. charybdis populations in late summer. In 2001 the wasp Baeoanusia albifunicle was The Eucalyptus Tortoise Beetle is the most identified in New Zealand as a hyper-parasitoid serious defoliator of eucalypts in New Zealand. which appears to have reduced the impact of A native of Australia, it was first detected in Enoggera nassaui on P. charybdis. A second the Port Hills in 1916 and is now distributed primary parasitoid wasp, Neopolycystus throughout the country. The beetle feeds on insectifurax, was also detected in 2001. In the foliage of about 60 eucalypt species, mainly the upper North Island parasitism of Paropsis those of the subgenus Symphyomyrtus. It is by Enoggera nassaui tends to increase between particularly attracted to E. nitens and November and January, declining in February. E. globulus. Feeding is restricted to the adult Activity of the hyper-parasitoid follows a similar foliage and results in characteristic scalloping trend, while that of N. insectifurax peaks later of leaf edges. Severe defoliation of flush foliage in the summer when temperatures are at their gives trees a sparse ‘broom top’ appearance. highest. The presence of N. insectifurax may Two generations are produced each year, the therefore compensate for some of the decline female beetles beginning to lay eggs a few in Ennogera nassaui populations in late weeks after the onset of the spring foliage summer. flush. Baeoanusia albifunicle does not develop Since 1987 the beetle has been controlled in successfully on N. insectifurax and cannot many parts of New Zealand by the primary develop in unparasitised P. charybdis eggs. parasitoid wasp Enoggera nassaui. This insect Enoggera nassaui has been recorded from lays its eggs in the beetle eggs and reduces Northland to Southland and is probably well Visit www.nzffa.org.nz for the most up-to-date information available. 51 established throughout the country. Recently, the hyper-parasitoid is likely to interfere with N. insectifurax