Target pest: Eriococcus coriaceus (Hemiptera: Eriococcidae), gum tree scale
Agent introduced: Rhyzobius ventralis (Coleoptera: Coccinellidae), gum tree scale ladybird
Cameron et al. (1989) - a ladybird referred to as Rhyzobius ventralis was imported from Australia against black scale (Saissetia oleae) in 1899; however, it seems the main Rhyzobius species introduced at this time was R. forestieri. As R. ventralis was already present in New Zealand prior to its 1905 importation against E. coriaceus the 1899 importation must have contained both R. forestieri and R. ventralis or there must have been more than one shipment around that time. In 1905 there were successive consignments of R. ventralis from Australia which were distributed widely against E. coriaceus.
Cameron et al. (1989) - successive importations of R. ventralis in 1905 were distributed widely in plantations infested with E. coriaceus. At the same time it was redistributed from Auckland [where it was presumably established from the 1899 importation - see Cameron et al. (1989) entry in 'Import notes' section] to South Canterbury, where the problem with E. coriaceus was most severe. It was also redistributed from 'breeding stations' in South Canterbury. Eriococcus coriaceus first reached the North Island in 1921 and in that same year large numbers of R. ventralis were shipped from the South Island to the North Island.
Cameron et al. (1989) - from the 1905 importations R. ventralis soon became established and spread readily where there were E. coriaceus populations. Redistribution from South Island populations to the North Island in 1921 [see Cameron et al. (1989) entry in 'Release details' section] resulted in rapid establishment in the North Island. It's present distribution is the Auckland region, Hawke's Bay, Bay of Plenty, Taranaki, Wairarapa and Wellington in the North Island and Marlborough, Nelson and Canterbury in the South Island.
Impacts on target:
Cameron et al. (1989) - the efficient and rapid control of E. coriaceus by R. ventralis is considered one of the great biocontrol successes against an insect pest in New Zealand. As a result of predation by R. ventralis, E. coriaceous is not now a major pest in this country. Small outbreaks of the scale have occurred as it has moved to new areas but artificial redistribution of R. ventralis (it has poor powers of dispersal) to these areas has successfully controlled the new infestations.
Withers (2001) - as a result of the introduction of R. ventralis, E. coriaceus is only problematic from time to time, in areas of Southland in the South Island and Bay of Plenty in the North Island. In these cases, 3 to 4-year-old Eucalyptus nitens are the worst affected and tree death can occur. Even in such circumstances, R. ventralis is usually present, and may be responsible for preventing such outbreaks from becoming even more serious.
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.
Withers TM (2001). Colonization of eucalypts in New Zealand by Australian insects. Austral Ecology 26: 467-476 https://doi.org/10.1046/j.1442-9993.2001.01140.x