Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

Privet Project Making Progress

Privet lace bugs.

Privet lace bugs.

In Issue 61 we shared some information with you about possible options for biocontrol of privet (Ligustrum spp.), which is an invasive weed causing problems in the North Island and in the warmer parts of the South Island. We can now update you on the two insects that have been identified as potential biocontrol agents.

Chinese privet (Ligustrum sinense) belongs to the family Oleaceae (which includes olives) and is also a major weed in the USA. A biocontrol programme has been underway there for some time now under the guidance of scientist Dr Jim Hanula from the USDA Forest Service. Jim is collaborating with scientists Yan-Zhuo Zhang and Jiang-Hua Sun from the Chinese Academy of Science in Beijing to determine the best candidate agents for privet control in the USA. The two most promising agents found so far are a sap-sucking lace bug (Leptoypha hospita) and a leaf-mining flea beetle (Argopistes tsekooni). Both the nymphs and adult lace bugs feed by piercing and sucking on the leaves, giving them a bleached appearance and causing dieback in the branch tips. The larvae of the leaf-mining flea beetle burrow between the upper and lower surfaces of the privet leaves. The adults tend to scrape the epidermal layer of the leaves often causing a small feeding hole. The combination of damage from the larvae and adult leaf-mining flea beetles usually leads to premature leaf fall.

We have been able to benefit from the US/Chinese work done to develop biocontrol for privet to date. “In 2013 we were able to obtain a shipment of the lace bug from the USA, and a shipment of the flea-beetle directly from China,” explained Quentin Paynter, who is overseeing the privet project in New Zealand. “Extensive host-range testing has already been conducted in the USA, so we know that many important species that belong to the Oleaceae are not at risk. However, Nestegis, which is the only native New Zealand genus in the Oleaceae, was not included in the USA research and needed to be tested before we could consider releasing the bug in New Zealand,” added Quentin.

Chris Winks has now conducted host-range testing of the lace bug inside the Tamaki containment facility and he has some good news to report. “The bug didn’t attack any of the four native Nestegis species, which is a positive step forward. Host-range testing is now focusing on the risk of non-target attack on ornamental lilac (Syringa spp.) varieties grown in New Zealand, the most closely related genus to privet present here, and should be completed soon. It appears that although the bug can rear through to adult on some Syringa species under laboratory conditions, survival is so poor that the risk of serious non-target attack in the field is likely to be very low,” said Chris.

The leaf-mining flea beetle is also currently in the Tamaki containment facility and is being reared to build up sufficient numbers to allow host-rang testing to begin. Based on host-range testing done with this species in the USA, it is expected to have a similar host-range to the lace bug, but may be more likely to damage lilac. However, this still needs to be thoroughly tested. As a bonus both agents are likely to also damage tree privet (Ligustrum lucidum). Once all the host testing is complete a decision will be made about whether to prepare an application to the Environmental Protection Authority to release one or both insects.

This project is funded by the National Biocontrol Collective.