Update on Essigella californica
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Formerly known as the Forest Research Institute, Scion has been a leader in research relating to forest health for over 50 years. The Rotorua-based Crown Research Institute continues to provide science that will protect all forests from damage caused by insect pests, pathogens and weeds. The information presented below arises from these research activities.
From Forest Health News 82, February 1999.
In July (FHNews 76: 1-2) we reported the discovery and known range of Essigella californica. At that time it was reported that the aphid appeared to be confined to the North Island with a southern boundary running from Wanganui in the west to Akitio in the east. It was also reported that larger numbers were encountered in the northern areas of its reputed range than in southern areas. Since then new locations have been reported from Wellington and Christchurch as a result of Port Environs Surveys. For all intents and purposes it would appear that we are witnessing the colonisation of New Zealand by a new insect. However we may on the other hand be looking at an artefact of our surveillance system superimposed on the boom and bust aphid life cycle. Up until last year E. californica had gone undetected because of its low numbers and the lack of any obvious damage. Our failure to find E. californica initially in the southern area of New Zealand may reflect very low numbers and subsequent finds corresponding to local seasonal increases in population and perseverance of our survey staff. As stated there is no evidence that E. californica is causing any damage to Pinus radiata in New Zealand. However the Australians are concerned that the aphid may be causing damage to P. radiata grown around Canberra. Symptoms are said to include defoliation and dieback starting at the crown and working two thirds the way down the stem. It is not certain that the aphid is causing these symptoms as the affected stands also have Cyclaneusma needle-cast and are suffering from a severe drought. It was also noted that by the time E. californica is recognised to be high and action taken, the population had crashed and disappeared.
(Geoff Ridley, Forest Research, based on material supplied by Clive Appleton, Margaret Dick, Gordon Hosking, Brent Rogan )
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