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Infestations in logs may be minimized by:
- The rapid turnover of stockpiles in the forest.
- A selection of unshaded skid sites.
- The stacking of logs on skids rather than on the ground (Milligan, 1978).
Logs for export can be mechanically debarked and treated with an insecticide (USDA, 1992).
Green sawn timber that is intended for export can either be kiln sterilized just prior to shipping or treated with an insecticidal dip (Milligan, 1978).
Seedlings can be protected from adult feeding damage by the use of controlled release granular insecticides (Reay and Walsh, 2002b). However, this measure is not usually necessary.
Biological control agents were imported into New Zealand, but only Thanasimus formicarius established. Because the larvae of H. ater are principally below ground, they are protected from natural enemies and T. formicarius is ineffective (Faulds, 1989).
Bevan (1987) stated that the damage caused by H. ater in Britain is severe and noted that over the years it has played a major role in causing planting losses, particularly of pine. Bevan also noted that it has proved to be rather more aggressive under British conditions than in many other parts of Europe. Munro (1917) recorded 45% mortality of newly planted Pinus sylvestris in a plantation in Britain.
Neumann (1979) stated that the damage is sometimes severe on nursery stock and young plantings in Australia but Elliott et al. (1998) noted that it is a relatively minor pest of Pinus spp., particularly Pinus radiata. However, Elliott also noted that in the early 1990s, 770 ha of second rotation P. radiata in Tasmania sustained numerous deaths of young seedlings.
Ciesla (1988) reported that up to 70% of pine seedlings in some areas of Chile have died as a result of H. ater attack.
Zondag (1965) reported that H. ater was the most troublesome insect in P. radiata regeneration in New Zealand and recorded over 50% mortality but with the qualification that it was only significant in poorly stocked areas. This implies that he was referring to natural regeneration and not planted areas. Clark (1932) reported that it caused severe loss in a young pine stand that had been re-established after logging operations.
Reay et al. (2001) discussed seedling mortality surveys that had been conducted within 1 year following planting in the central North Island of New Zealand. Seedling mortality in most forest compartments was less than 5% but was as high as 30% in a few compartments. The destructive sampling of seedlings showed that there was a high level of sub-lethal attack on seedlings, it was greater than 50% in two-thirds of the compartments sampled. Similar results were reported from a trial in the South Island of New Zealand much earlier, where 82% of seedlings had superficial resin-encrusted wounds on the stem base and larger roots (New Zealand Forest Service, 1970). Obviously the sub-lethal or abortive attack on seedlings is very common and it would seem that the presence of feeding damage or the beetles themselves on dead seedlings is not conclusive evidence of cause and effect. Milligan (1978) suggested that in general healthy seedlings do not succumb to adult feeding and that those seedlings that do die are in some way debilitated or weakened by environmental factors such as extreme climatic conditions and poorly aerated soils. Several writers have observed that the quality of nursery stock and its treatment prior to and during planting, affect its susceptibility to damage by H. ater (e.g. Munro, 1917; Clark, 1932).
Reay et al. (2001) suggested that there might be ramifications from the adult feeding on seedlings on future wood quality because it is known that the beetles can carry sapstain fungi to seedlings. The following species of sapstain fungi have been isolated from H. ater in New Zealand: Ophiostoma ips, Ophiostoma setosum, Ophiostoma querci, Ophiostoma huntii, Ophiostoma galeiformis, Ophiostoma pluriannulatum, Leptographium truncatum and Leptographium procerum. The following fungi have been isolated from surface-sterilized seedlings following attack by H. ater: O. galeiformis, O. huntii, O. setosum, O. querci, Ophiostoma floccosum, Ophiostoma piceae, L. procerum and L. truncatum (MacKenzie, 1992; Reay et al., 2001). It would be of interest to know what species of fungi could be isolated from seedlings that have not been attacked by H. ater. Clearly more work is warranted.
Pasek (1998) suggested that there is the potential for H. ater to vector root diseases associated with intensive management. In England, several species of sapstain fungi can be consistently isolated from brood galleries of H. ater. These include Ophiostoma coerulescens, Ophiostoma penicillata (Dowding, 1973), Leptographium serpens and Leptographium sp. (Wingfield and Gibbs, 1991).
In New Zealand, infested logs are either refused for export or must be treated (usually by fumigation) immediately before shipping. Green sawn timber for export may also have to be treated (fumigation or kiln sterilization) if the adults that have been attracted to the freshly sawn wood are present. Sapstain fungi are transmitted by the beetles to the outer sapwood of logs but rarely significantly penetrate unless there is abnormal delay between felling and sawing (Milligan, 1978).