Report on the Levels of the Scale Insect Pulvinaria Urbicola and its Natural Enemies on Pisonia Grandis
in the Coringa-Herald National Nature Reserve 16-23 March 2001
D. Smith and D. Papacek
Report for Environment Australia, March 2001
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About this document
Pulvinaria urbicola levels on Pisonia grandis on North East Herald Islet in the Coral sea have increased 150 fold since the last assessment in December 1997.
- The infestation has spread through the islet with many hot spots with scale numbers over 100 per leaf.
- No parasitoids were recorded and there is little if any predation.
- Similar scale levels were recorded on Coringa Islet in December 1997 where there is now only one small heavily infested tree left.
- There is a serious threat of major damage occurring on North East Herald during the next 6-12 months followed by total destruction of the Pisonia forest.
- The scale can be regarded as an exotic pest to Australia normally biologically controlled by two small wasp parasitoids Coccophagus ceroplastae and Euryischomyia flavithorax and the ladybird Cryptolaemus montrouzieri.
- These natural enemies effectively control the scale in Eastern Australia and the two parasitoids are very effective on islands of the Capricorn Group.
- The only exception to this is Tryon Island where until recently, parasitoid numbers were low or absent.
- It is recommended that immediate action be taken to introduce C. ceroplastae, E. flavithorax and C. montrouzieri primarily to North East Herald but also to Coringa and South West Herald Islet.
- The parasitoids need only to be released in numbers of several hundred to 3000. These should be reared from green coffee scale and from P. urbicola on the mainland and released as soon as possible- either before winter or in the spring 2001.
- The ladybird C. montrouzieri is commercially available and can be released at similar times.
- The scale attacking fungus Verticillium lecanii is another biocontrol option.
- Dispersal of P. urbicola to the Coral Sea Islets may have been by sea birds. Human involvement appears less likely.
- South East Magdelaine Islet appears to be free of the scale and particular care must be taken by visitors not to accidentally infest the islet.
- Two ant species, Tetramorium sp. and Monomorium sp. were collected in close association with P. urbicola infestation. They currently appear to be playing a minor role in the population dynamics of the scale.
- The former P. grandis forest area on Coringa Islet is now dense herb land. Achyranthes aspera, Portulaca oleracea and Ipomoea spp. were heavily infested with P. urbicola on Coringa.
- A. aspera on South West Herald had been heavily infested but levels had subsided and a new scale generation was present on young growth.
- Revegetation of Coringa with P. grandis trees will depend initially on successful biocontrol of P. urbicola on the alternate hosts. A programme of rooted plant establishment and minimal horticultural maintenance will need to be considered. The heavy herb land growth will require control at planting sites. Pisonia would best be reestablished in stands where care could be concentrated and the typical undertree environment fostered.
- Visitors to the Coral Sea Islets should be aware of a quarantine protocol which should prelude introduction of soil, firewood or vegetative material. All fresh fruit and vegetable scraps including the rind of fruit should be carried off the islets. Equipment should be clean and free of dirt, insects, spiders or small animals. Visitors should be careful not to transfer organisms between the islets particularly at this stage to SE Magdelaine Islet.
