TECHNICAL
PROMISING START FOR BIOLOGICAL CONTROL OF TOMATO POTATO PSYLLID Words by Sally Anderson, VR&I co-ordinator
Since the Tomato Potato Psyllid (TPP) was discovered in New Zealand in 2006 this small insect has caused problems for New Zealand’s potato, tomato, capsicum and tamarillo growers. Since then, growers have been waging a battle to control this insect pest. TPP cannot be eradicated and can only be controlled. Early on, industry recognised that solely relying on insecticides to control TPP was not sustainable. Although several existing natural enemies do attack TPP already in New Zealand (e.g. lacewings and hoverflies), these are already widespread in the horticultural environment and do not need to be released. An additional ‘tool in the toolbox’ in the form of a biological control agent (BCA) was added to growers’ armoury in 2016, when New Zealand’s Environmental Protection Agency approved the importation and release of Tamarixia triozae, a parasitic wasp of TPP. This approval was the critical first step and marked the beginning of a three-year Sustainable Farming Fund (SFF) programme to improve the control of TPP with Tamarixia funded by the Ministry for Primary Industries (MPI) and TomatoesNZ, Vegetables New Zealand, Potatoes New Zealand, the NZ Tamarillo Growers Association and Heinz-Wattie’s NZ Ltd.
The goal of the SFF programme was to establish selfsustaining populations of Tamarixia in New Zealand, to contribute to the control of TPP. This project was the first time that Tamarixia has been released as a classical BCA anywhere in the world. Classical biological control involves the introduction of a natural enemy of exotic origin to control a pest that is also often exotic. The goal of the programme has been achieved. The SFF programme officially started on 1 July 2016 and finished on 30 June 2020. Following the importation of Tamarixia into quarantine facilities at Plant & Food Research (PFR) and approval to release progeny of the imported parasitoid by MPI, the first releases were carried out in late 2017 by PFR staff. Tamarixia was released onto African boxthorn (a non-crop host of TPP) at sites in the Hawke’s Bay and Canterbury. Small numbers of Tamarixia (batches of ~500) were released, and over the following two years PFR has re-surveyed these sites to see if Tamarixia were still present. The great news from these surveys was that Tamarixia were able to survive two consecutive winters, as the PFR team found evidence of Tamarixia parasitising TPP at these locations. This finding confirmed that Tamarixia can establish self-sustaining populations in New Zealand where year-round populations of its TPP host can survive and environmental conditions are favourable. Given the relatively small numbers of Tamarixia released at these sites in Year 1, this is a remarkable result. In addition to demonstrating over-wintering survival, follow-up surveys have shown that where conditions are favourable Tamarixia can spread quite large distances. This was especially true in the Hawke’s Bay where parasitised TPP were detected up to 24km from the nearest release site and were found at 25 of 86 non-release sites surveyed in this region by PFR staff.
Tamarixia triozae is a tiny wasp (approx. 1mm long), that lays its eggs on the psyllid nymph, which then hatch and eat the psyllid. The photo shows Tamarixia about to parasitise a TPP nymph. (Photo supplied by: Plant & Food Research) 58
NZGROWER : AUGUST 2020
