The New Zealand Institute for Plant & Food Research Limited Expert presentation. For EPA hearing on Tamarixia triozae John Charles, PFR, Auckland.
Overarching comments on host-testing 1. There is no universal method for selecting non-target species for host-testing. See BIREA for discussion. 2. The selection process carried out by Dr Gardner-Gee broadly followed the approach of Kuhlmann et al. 2006 which I regard as ‘best practice’. 3. Experiments on parasitoid behaviour are always constrained by the physical requirements of containment. Simple experiments often give the clearest indications of risk. The New Zealand Institute for Plant & Food Research Limited
Overarching comments on host-testing 4. Biocontrol operates on populations. Death of a few individuals does not mean that populations are at risk. 5. It might simply not be possible to quantify risks illuminated by laboratory tests. In essence insect behaviours and the biotic and abiotic interactions in wild biological systems are simply too complex to ever “convincingly predict the likelihood of displacement and other adverse impacts” from laboratory experiments. The New Zealand Institute for Plant & Food Research Limited
Response to DoC submission 2. “There are 50 endemic species within the family Triozidae. The application has acknowledged the parasitoid could establish in areas where Triozidae endemic species are found given their distribution overlaps with TPP. Of these 50 species, only four were tested for their suitability as hosts. The parasitoid showed an interest in two (50%) of these four ( Trioza curta and Trioza panacis ), successfully emerging from one (parasitized T. panacis ). These results indicate the parasitoid’s clear interest in our native Triozides family representatives.” Response: “Clear interest” implies that T. triozae will preferentially seek out our native psyllids as a novel resource. I don’t think the data support this view. The New Zealand Institute for Plant & Food Research Limited
Response to DoC submission From this limited host testing, we cannot confidently state T. panacis is likely to be the only species vulnerable to T. triozae parasitism. Response: The testing never confidently stated that T. panacis was the only species that would be attacked; and I don’t think it ever stated that T. panacis was “vulnerable”. This reflects a difference between individuals (those attacked are clearly vulnerable) and populations or species (that may be at risk of attack, but are not necessarily vulnerable). The New Zealand Institute for Plant & Food Research Limited
Response to DoC submission 4. We argue the decision to exclude three sub-groups from the Genus Trioza – a genus containing a range of species of preference for T. triozae parasitism - on the grounds that these sub-groups are not well represented around Auckland, is a short-sighted view and lacks rigour. Budget constraints are unfortunate, but should not be used as a reason for perfunctory decisions where consequences may be irreversible. We consider that more tests are required on additional native Triosid psyllids that overlap with the likely distribution of T. triozae throughout New Zealand, not just around Auckland. Response: Absence of a species from Auckland was only one of the criteria for not testing species. Even so, having concluded that there is a risk, how many more tests are justified? What would they demonstrate? The New Zealand Institute for Plant & Food Research Limited
Response to DoC submission 5. It does not follow that because “ T. triozae is an obligate parasitoid which relies on psyllid hosts for its survival” that “the likelihood that T. triozae will cause significant displacement of non-target native psyllid species that are not its preferred host is … highly unlikely” (p 19) . The likelihood of displacement and other adverse impacts can only be convincingly predicted by rigorous host testing and/or field studies. Response: There are, unfortunately, limits to what can be achieved by laboratory tests. Studies from overseas indicate that it simply might not be possible to quantify risks shown by laboratory tests. In essence insect behaviours and the biotic and abiotic interactions in biological systems are simply too complex to ever “convincingly predict the likelihood of displacement and other adverse impacts”. So further host testing in containment would probably not add to our ability to quantify risk; and clearly we cannot carry out field studies. The New Zealand Institute for Plant & Food Research Limited
Response to DoC submission 6. Given the very limited level of host testing on native Triozidae we do not support the conclusion near the end of Section 5.2.1 (p 45) “ We can only conclude that T. triozae may parasitise a small proportion of native psyliids in the Triozidae family. Given the indication that T. panacis is not an optimal host, we consider that the likelihood that non-target parasitism by T. triozae might result in population level effects and significant displacement of native psyllid species is low”. Response: Regardless of the limited testing, the data showing lower fitness of F1 Tamarixia triozae reared on Trioza panacis do, in my opinion, indicate that this psyllid is unlikely to be able to sustain a permanent population of T. triozae in the wild. The New Zealand Institute for Plant & Food Research Limited
Response to DoC submission 7. Finally, we note that the adult female T. triozae is a predator (p 13) as well as a parasitoid. The report states the female uses her ovipositor to stab and mutilate the TPP nymph, to enable feeding on haemolymph. The host feeding of the TPP nymph stages by female T. triozae are said to be as significant as parasitism in harming TPP. It does not appear as though NZ’s native Triozidae species have been tested for vulnerability to predation. We consider this a significant gap in meeting the minimum standards. Response: Host-feeding by a female parasitoid is a behavioural function of her attack and oviposition strategy. It does not act as an independent ‘predatory’ mortality factor in the same way as a predator. In other words, a female T. triozae will not search out native psyllids as a predator alone. Predation is only associated with the likelihood of parasitism, and it is encompassed in the ‘risk’ already associated with the parasitoid. The New Zealand Institute for Plant & Food Research Limited
Response to DoC’s conclusions DoC concludes that: a. most native species were not represented in host testing so we cannot accurately predict which NZ species are likely to be suitable hosts for the parasitoid Response: I agree that most native species were not tested. But repeat that a more accurate prediction could only ever be approached by testing every species – which is logistically and financially not possible. b. non-target native psyllid species on non-crop host species have been insufficiently factored into the assessment Response: The rationale and methods for selecting the non-target species that were tested are described in Dr Gardner- Gee’s report . I think they were appropriate. The New Zealand Institute for Plant & Food Research Limited
Response to DoC’s conclusions c. the limited host testing done on native Triozid species demonstrates 50% are likely to be adversely impacted via parasitism where distribution overlaps Response: I disagree. First, the testing demonstrated that two of four species of Triozidae were attacked, although - given a choice - T. triozae females laid fewer eggs on the native species than on TPP. This certainly does not equate to ‘50% of all native Triozids are likely to be attacked’. Second, T. curta did not allow complete development of T. triozae so would not allow a self-sustaining population of the parasitoid to develop. T. panacis did support complete development of the parasitoid, but evidence indicated that the F1 generation was less fit, such that T. panacis would also not be likely to sustain a population of the parasitoid. This evidence does not support a conclusion that any native parasitoid “is likely to be adversely impacted via parasitism”. The New Zealand Institute for Plant & Food Research Limited
Response to DoC’s conclusions d. predation levels on NZ native species has not been assessed at all Response: Tamarixia triozae is not a predator. The ‘host - feeding’ behaviours are encompassed within the risk already identified. The New Zealand Institute for Plant & Food Research Limited
The New Zealand Institute for Plant & Food Research Limited www.plantandfood.com John.Charles@plantandfood.co.nz
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