with regard to the releasing of parasitoids and ladybird predators of the pest scale Pulvinaria urbicola on Pisonia grandis
Dan Smith1, Dan Papacek2 and Jonathan Smith3
1. Senior Principle Entomologist, Qld Horticultural Institute, PO Box 5083, SCMC, Nambour, 4560, Qld.
2. Entomologist/Director, Bugs for Bugs, Bowen St, Mundubbera, 4626, Qld.
3. Research assistant, 13 Baloo St, Nambour 4560, Qld.
About this report
- Collect and rear the small wasp parasitoids (mainly Coccophagus ceroplastae and Metaphycus sp. and the ladybird Cryptolaemus montrouzieri on the mainland in preparation for re-release on NE Herald.
- Re-release the parasitoids on NE Herald with the aim of confirming establishment.
- Re-release C. montrouzieri in scale pockets on NE Herald. Treat for ants if necessary.
- Reassess levels of pulvinaria scale on Pisonia and ant levels.
- Determine if the parasitoids and ladybirds released in August established and their levels in the scale. Reassess scale levels on Acharanthus on SW Herald, assess presence of natural enemies, release C. montrouzieri and treat for ants if necessary.
Ladybird and parasitoid releases: Coccophagus ceroplastae was multiplied on Pulvinaria urbicola on young potted Pisonia plants during September - December 2001. These Pisonia plants were derived from thick (2-4 cm) wood cuttings brought back from NE Herald in August. They were dipped in Clonex (Gel-Green 1.5g/l indole 3 butyric acid) and rooted in river sand in a mist bed with bottom heating. Establishment of C. ceroplastae (coming out of late winter) was slow but there were moderate levels by mid December. The scale and parasitoid infested shoots were pruned off on 15 December, leaves removed and the shoots dipped in a mixture of benomyl fungicide and the miticide abamectin.
Metaphycus sp. was taken as adults in ten 500 ml tubs. C. montrouzieri was again supplied free of charge by Dan Papacek of the 'Bugs for Bugs' Insectary at Mundubbera with a total of 20 tubs totalling about 10 000 adult beetles. The Metaphycus and Coccophagus were released on 18 December in transect 8 (the northern end within the first 100m) where there was the greatest concentration of scale (surviving C. montouzieri predation since release in August). The scale/parasitoid infested Pisonia twigs were hung in 8 small tubs (ant proofed) to allow progressive emergence of Coccophagus over the next 2 weeks. The release area was treated for ants with a ground dog biscuit (Lucky Dog 15% protein, 10% fat, 5% fibre) fipronil bait (100 ppm) at a rate of 2.5 kg/ha.
Fresh beetle releases were made in transects 4 (60m), 5 (440m), 6 (280 and 480m), 8 (160, 340 and 370m) and 9 (30m) totalling about 7000 beetles on 18-20 December. The remaining 3000 beetles were released on SW Herald (interior SW corner) on 20 December.
The area of release was 200m by 50m or 1ha (and this was treated with the dog biscuit fipronil ant bait).
Scale, ant and natural enemy assessments: Scale/leaf samples were made (as described in Report No 1, 16-23 March 2001). Counts were made every 60m. Scale samples were collected, examined using a binoc stereoscope on the island and stored in mesh tubs and tubes for further examination/rearing out on the mainland.
Counts of the transects of NE Herald made on 19-20 December are listed in Appendix 1. Results are summarised in Table 1.
Scale levels: The most heavily scale infested transect was No 8 with a total of 415 live scale (172 first, 171 second and 72 third instars). Transect 2 had 95 scale, transect 5 - 55, transect 11 - 52 and transect 6 - 41. Transects 1, 3, 4, 7 and 10 were almost scale free. The scale average per cm of leaf index was 0.18 compared with 0.43 in March 2001. The same index for just transects 2, 4, 6 and 8 in December was 0.30 as compares 1.48 in August and 0.33 in March. Whereas dead trees were evident in transects 1, 2, 6 and 8 especially on the northern edge in August, there was little evidence of dead trees in December.
The period from August - December must have been very dry as evidenced by water stressed Argusia argentea and by the dryness of the sand above the high water mark. This had also stressed the Pisonia forest but possibly the only evidence of this was a smaller average leaf length in the samples - 12.04cm in December in comparison with 20.4cm in August and 19.02cm in March. There was no evidence of leaf wilting in the Pisonia.
Ant levels: Total ant numbers were 238 Tetramorium sp. and 3 Monomorium sp. This compares with 339 and 36 for the same number of sites in March. Transects 2, 4, 6 and 8 in December had 165 Tetramorium sp and 0 Monomorium sp. as compared with the same transects in August of 731 and 16 respectively. Ant numbers had fallen then approximately 4 fold since August and by 30% in comparison with March.
Predatory beetle levels: C. montrouzieri levels had obviously greatly escalated since releases in August. In December, 87% of all scale infested leaves had evidence of beetle activity most of it in the previous 2 months. Out of a total of 1053 adult egg producing scale, only 9 were free of beetle activity, 993 had been eaten out and 51 were currently under attack. The beetle has almost destroyed the scale populations in every transect except 8 and is currently very active there.
On SW Herald, vegetation was severely affected by the dry conditions and species like the herbaceous Acharanthes aspersa, Portulaca oleracea and Tribulis cistoides (hosts of the scale) were much reduced with many dead plants. Live A. aspersa was heavily infested with scale and specimens were collected. Subsequent examination showed them also to be heavily infested with C. montrouzieri larvae. It must be calculated that the beetle had spread some 12km from NE Herald in the previous 3 months. It is evident that a very large population of beetles has developed on NE Herald with many dispersing adult beetles looking for food.
Wasp parasitoids: Establishment of Euryischomyia flavithorax and Metaphycus sp was confirmed with E. flavithorax the most numerous particularly on the northern edge of transect 10 on NE Herald where about 50 out of 60 second instar scales on one leaf were parasitised by this species. There was no confirmed instance of Coccophagus ceroplastae.