China likely source of Asian gypsy moth larva

Asian gypsy moth

The value of good record keeping – and good detective work – has been demonstrated with the naming of the port of Yantian, China, as the likely pathway of an Asian gypsy moth larva found on a sea container in Auckland.

The Biosecurity Monitoring Survey team found a mature larva of a lymantriid moth on the underside of a loaded container leaving the Ports of Auckland during a survey. It was identified as gypsy moth, Lymantria dispar (Lepidoptera: Lymantriidae) by morphological characteristics, and genetic testing confirmed that it was the Asian form of the species, usually known as Asian gypsy moth (AGM).

The larva was dead and desiccated, but intact, and still brightly coloured with a shiny clean cuticle. It had not been attacked by arthropods that often shelter underneath containers. This suggests that this larva was from the 2006 breeding season.

The container was loaded in Sydney on 7 September 2006 with packages of high-density polyethylene, and arrived in Auckland 12 September, destined for de-vanning at a transitional facility in South Auckland. AGM is not present in Sydney, indicating that the larva must have originated from a previous voyage of the container.

The lessee of the container, Mediterranean Shipping Company (AUST) Pty Ltd, provided information on the container's movements during the two-and-a-half years prior to its departure from Sydney. The date range was chosen in view of the apparent freshness of the larva. During this period, the container had completed 36 voyages. From June 2004 – October 2005, it was mainly used on southern European and Mediterranean routes, with more recent voyages including China.

AGM occurs throughout temperate Asia, although the boundary between the 'Asian' gypsy moth and 'European' gypsy moth is not strictly defined. Most interceptions at the New Zealand border are from far eastern Asia, especially Russia and Japan. With the most likely origin of the larva being eastern Russia, Korea, northern or central China or Japan, four voyages stood out as possibilities (see Table 1).

AGM larvae are present in China mainly during April, May and June. The exact timing of hatching and development depends on altitude and latitude as well as weather, population density and other local conditions, making the exact timing difficult to predict. It is likely that this larva, being mature, would be prospecting for a pupation site towards the end of the two-month larval growth window.

The most likely origin of this specimen is China in 2006. Both the nine days at Busan in June 2004 and the 30 days at Yantian fit the time frame. It is unlikely, however, that the larva would have arrived in such excellent condition after two-and-a-half years of exposure to the elements, decay and predation. Although Yantian (near Hong Kong) is further south than the reported range of Asian gypsy moth in China, the available details only indicate that the container entered and left China via Yantian; it may have travelled elsewhere within China during the 30 days between arrival and departure. It is likely that the larva crawled onto the container at some place either inland or north of Yantian.

The periods ashore at Shanghai and Chiwan, in October 2005 and January 2006, respectively, are when AGM is dormant as egg masses; live larvae would not be present during these months. The evidence suggests that the larva originated in the Yantian region during June–July 2006.

Information from this interception will be used to re-evaluate MAFBNZ's sea container risk profile and inform risk analysis for AGM.

Table 1: Most likely voyages to be source of AGM larva on container

Discharge port Arrival date Loading port Days ashore
Busan, South Korea 28/05/2004 Busan (transhipment) 9
Shanghai, China 17/10/2005 Shanghai 18
Chiwan, China 8/01/2006 Chiwan 37
Yantian, China 25/06/2006 Yantian 30

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Page last updated: 2 July 2010