Tomatoes & TPP Biocontrols

The tomato potato psyllid TPP (Bactericera cockerelli), was first detected in New Zealand in 2006. TPP has had a devastating impact on commercial crop growers of plants such as tomatoes, potatoes, and tamarillos. Researchers at the BioProtection Research Centre based at Lincoln University are conducting trials with four possible biocontrol agents – looking for an effective combination for controlling TPP in tomato crops growing in glasshouses. Professor Steve Wratten says it is likely to be a problem across all commercial hothouses in New Zealand.

Presently growers rely on broad-spectrum insecticides but they are proving to be a blunt instrument, as they also kill beneficial insects, such as the parasitic wasp that fights whitefly. And there’s the additional issue of TPP developing resistance to current insecticides. Steve says identifying effective biocontrols are paramount, especially as pesticide companies are developing fewer new products. A chemical company representative has been quoted as saying, “The cavalry is not about to come over the hill - there are no replacements”.

Steve Wratten is supervising research into TPP biocontrol for hothouse tomatoes. Initial work was funded through the Sustainable Farming Fund and Plant & Food Research (PFR). The Agricultural and Marketing Research and Development Trust (AGMARDT), Tomatoes NZ and Vegetables NZ have now supported it. AGMARDT funding has allowed post-doctoral research to be carried by Dr Shola Olaniyan.

Research shows that biocontrol agents when working in combination may be more effective than by themselves, as long as there is limited interference between them. The 4 biocontrols they’re presently looking at are: the Southern ladybird (Cleobora mellyi), a mirid bug (Engytatus nicotianae), a predatory mite - Amblydromalus limonicus, and the Mexican wasp - Tamarixia triozae.

Each bug has been identified as a possibility through prior research and an understanding of related species and the species they prey on.

The Southern ladybird, Engytatus nicotianae and Amblydromalus limonicus tend to feed on the second and third stage nymphs. All will eat the TPP eggs but Engytatus nicotianae only occasionally. At this stage there is not a biocontrol option that eats TPP adults.

The Mexican wasp from South America is a naturally occurring parasitoid of Tomato Potato Psyllid. It lays eggs mostly on the 4^th and 5^th stages of TPP nymphs. The eggs hatch into larvae and then feed on the psyllid. 

The Southern ladybird was not a natural predator of TPP – it was a ‘new association biological control’ in that it had not previously met the Tomato Potato Psyllid. Earlier research overseen by Wratten established the potential of Southern ladybird as a biocontrol for TPP control in potatoes. Further, it showed that companion planting of buckwheat providing the ladybird with additional nectar returned more positive results than just the ladybird feeding on the TPP. However, the ladybird did not persist when released in a potato field, perhaps due to the timing of release (autumn). It is hoped that it will be a more effective control agent within enclosed glasshouses.

Engytatus nicotianae belongs to a family of bugs that feed on both plants and other insects. Some European and North American research has suggested that close relatives of this species; Engytatus varians and Dicyphus hesperus respectively, are effective against TPP. It is uncertain how the bug arrived in New Zealand but as it is present here already and doesn’t require the stringent and lengthy process to approve it for research, the researchers have included it in their work.

The Predatory mite Amblydromalus limonicus is an experimental inclusion. Initial trials suggested it might be more effective than the others for controlling TPP nymphs but the researchers think it might have been the sheer number of the mites used, that produced the initial results. Lower numbers of the mite will be used in a second trial to confirm if it is truly effective on tomato plants, which have hairs that produce a waxy secretion that may restrict the mite’s movements. The mite is currently used in Europe as a biocontrol for thrips, whitefly and spider mites in commercial glasshouse production of cucumber and ornamental crops.

This research is presently collecting baseline data on the effectiveness of each bug specifically against TPP in hothouse tomato crops. They’re also running a combination of the wasp and Amblydromalus limonicus and the wasp and mirid bug, Engytatus nicotianae.

The research also has combinations of the tomato plants with buckwheat plants. Buckwheat is a non-crop plant often planted at a crop edge or amongst the crop to enhance the performance of biological control agents by providing nectar and pollen, which increases longevity and/or the number of eggs laid by agents.

Once baseline data is established, the plan is to look at other possible combinations to ascertain the most effective combination for controlling TPP. It is hoped they can then move to commercial glasshouses and work with commercial growers to test the biocontrols under those conditions.