Spread of Dicranosterna semipunctata (Col.: Chrysomelidae) in New Zealand and potential for control by intentionally introduced and invasive parasitoids

The Australian beetle Dicranosterna semipunctata (Chrysomelidae) was detected in New Zealand in 1996. The beetle has become a pest of Acacia melanoxylon (Mimosideae) and spread at a rate of approximately 20 km/yr. Two egg parasitoids reared from D. semipunctata in its native range have been identified as prospective classical biological control agents but have not been introduced. The egg parasitoid Enoggera nassaui (Pteromelidae) and the predatory beetle Cleobora mellyi (Coccinellidae), introduced into New Zealand as biological control agents for the Eucalyptus defoliator Paropsis charybdis (Chrysomelidae), have also been considered as control agents for D. semipunctata. However, E. nassaui, does not parasitize D. semipunctata eggs in the field and C. mellyi has been slow to establish and its impact on D. semipunctata remains unknown. Prospects for biological control of D. semipunctata were boosted in 2009 with the appearance of a new egg parasitoid, Neopolycystus sp. This represents the third known incursion into New Zealand by an Australian parasitoid associated with paropsine beetles in less than 10 years. Field surveys confirm that the parasitoid has established in several North Island regions, parasitizing D. semipunctata eggs between December and March. Neopolycystus sp. is expected to play a significant role in the future suppression of D. semipunctata in New Zealand.

Highlights► Acacia pest Dicranosterna semipunctata has spread at a rate of 20 km/yr in New Zealand. ► Biocontrol agents introduced against related eucalypt pest contribute little to its control. ► Prospective biocontrol agents have been identified in Australia but none intentionally introduced. ► Self-introduced egg parasitoid detected and shows potential to suppress pest.