Biocontrol introduction
Target pest: Asterodiaspis quercicola (Hemiptera: Asterolecaniidae), pit scales
Agent introduced: Habrolepis dalmanni (Hymenoptera: Encyrtidae)
Imported:
1923, 1924, 1925, 1926, 1927, 1928
Import source:
Massachusetts, USA
Import notes:
Cameron et al. (1989) - eight shipments of H. dalmanni in scale hosts on oak twigs collected in Massachusetts, USA were received from the Bureau of Entomology, Washington D.C. between January 1923 and March 1928. A total of 875 adults emerged from these consignments; those that survived were released into insectaries or into the field.
Released:
1923
Release details:
Cameron et al. (1989) - a total of 784 adults emerging from imported parasitised hosts were released, into insectaries or into the field, at Christchurch (Canterbury) and Nelson in the South Island. In Christchurch, nine adults were released in 1923 (insectary and field release) and 159 in 1928 (into the field). There were five Nelson releases between 1924 and 1928; in total 152 adults into an insectary, 464 into the field. Many thousand H. dalmanni were redistributed from established field populations in Nelson (1929-38) and Christchurch (1936-37) to Northland, Auckland, Hawke’s Bay and Taranaki in the North Island and Christchurch, North Canterbury, South Canterbury and Dunedin (Otago) in the South Island.
Establishment:
Cameron et al. (1989) - a few adults were recovered in Christchurch in the summer following the February 1923 release, but from then until 1928, when numerous scales parasitised by H. dalmanni were found on a single tree where only a few females had been released six months beforehand, no parasitoids were observed. (Although the curator of the Christchurch Botanic Gardens claimed in 1927 H. dalmanni had controlled Asterodiaspis spp. in the Gardens.) By 1933, the parasitoid was spread throughout Christchurch and even to Akaroa, 33 km away. Habrolepis dalmanni was first released in the field in Nelson in December 1925 and there was evidence by March 1926 it had established there. By 1929 it was widespread in Nelson.
Impacts on target:
Cameron et al. (1989) - late in 1933, relatively high levels of parasitism of Asterodiaspis spp. by H. dalmanni were reported in a central Christchurch park (27%), the Christchurch Botanic Gardens (38%), in Christchurch suburbs (22%) and in Akaroa (53%). In Nelson in February 1934 parasitism was 60%. In New Zealand H. dalmanni has provided sufficient control of Asterodiaspis spp. in ensure improvement in the health of oak trees. However, unhealthy trees with many unparasitised scales were found in the vicinity of the parasitoid release area in Christchurch in 1988, therefore only partial control has resulted.
Cameron et al. (1993) - Habrolepis dalmanni is categorised as exerting “substantial” control (defined as “other control measures are only occasionally required”) over Asterodiaspis spp.
References
Cameron PJ, Hill RL, Bain J, Thomas WP (1989). A Review of Biological Control of Invertebrate Pests and Weeds in New Zealand 1874-1987. Technical Communication No 10. CAB International Institute of Biological Control. DSIR Entomology Division. 424p.
Cameron PJ, Hill RL, Bain J, Thomas WP (1993). Analysis of importations for biological control of insect pests and weeds in New Zealand. Biocontrol Science and Technology 3(4): 387-404
