Post Release Evaluation – Not just an Expensive Luxury!

Posted by Hester Williams @HesterW123


Classical biological control, i.e. the introduction and release of non-native insects, mites, or pathogens to give permanent control, is the predominant method in invasive plant biocontrol. A successful biological control programme eventually reduces, or in some cases removes, the need other methods of control for an invasive species that is growing prolifically in the absence of its natural enemies. The benefit-to-cost ratio of successful control can be very high, especially when earlier successes in one country form the basis for repeating the introductions elsewhere.

New Zealand has a long history in biological control of invasive plants and is one of five countries that are very active in this field. In a recent analysis on the benefits of biocontrol in New Zealand it was found that 30 % of releases (of those that could be assessed because of sufficient passage of time) resulted in significant beneficial effects. Cases with negligible benefit (36%) included agents that failed to establish, and cases with minimal benefit (33%) included some cases where predation reduced the realized benefit of established agents.


Post-Release Evaluation

An important component of all biocontrol projects is Post-Release Evaluation, the process of assessing how successful the projects have been and to understand why they succeed, fail or achieve intermediate results, and to determine and evaluate any non-target effects. Such information would not only provide better justification for biocontrol funding, but would also inform the agent selection process for subsequent projects, assist in the improvement of pre-release screening, help to increase establishment success and provide gateways to integrating biocontrol with other management practices.

Identifying biocontrol successes

Remarkable successes have been achieved through biocontrol projects, including the

St johns wort and beetle

Chrysolina sp., one of the biocontrol agents that is contributing to the successful control of St John’s wort in NZ.

control of St John’s wort (Hypericum perforatum) which used to be one of the worst four weeds in New Zealand. This plant displaced pasture in the dry high country and poisoned stock. Two beetles that defoliate the plant and a midge that stunts growth by deforming the plant were released as part of the biocontrol programme. The lesser St John’s wort beetle was the first to be released in 1943, while the greater St John’s wort beetle and the gall midge were released about 20 years later. All three agents established and today the plant has declined to the point where it is no longer considered a problem. A recent economic analysis has estimated that the Net Present Value of introducing the beetles is between $140 and $1490 million over 70 years, a benefit to cost ratio of 10:1 and 100:1 respectively. A remarkable return on investment!


Identifying biocontrol failures

Biocontrol programmes of course do not always result in successes, and failures are inevitable. Failures include inability of released agent populations to establish, or underperformance of agents. For example, here in New Zealand, the heather beetle (Lochmaea suturalis), has underperformed as a biocontrol agent when compared with the damage it does to native heather in Europe. Post-release evaluation studies have indicated that the smaller body size of beetles in NZ, probably mostly due to a severe founder effect, resulted in higher winter mortalities and therefore underperformance of the beetle in NZ. In 2014, an effort to genetically rescue the NZ population was undertaken; more beetles were collected from Scotland and mated with New Zealand beetles. These new genetic lines of beetles were released in November 2014 and currently post-release evaluation studies are underway to confirm establishment. Future studies will compare the performance of the new and original populations. This project represents a novel approach to explore the possibility of enhancing the performance of already established biocontrol agents so that they can better adapt to the local conditions and more effectively control the target weed.

Identifying Non-target effects of biocontrol

  • Direct risk to non-target plant species (usually closely related species).
Rhynocyllis larvae

Rhynocyllis  conicus, a biocontrol agent for musk thistle in the USA, also utilizing native thistle species.

The case of the weevil Rhinocyllus conicus is particularly well known. First introduced from France to North America in 1968 to control invasive musk thistle (Carduus nutans), then widely distributed in the United States, this seed predator utilizes at least 22 native species of Cirsium in North America, including some species of conservation concern that have been shown to be seed-limited. Additional studies have found that the observed level of seed predation by the weevil to not be sufficient to limit seedling recruitment.

  • Indirect non-target effects, for example, via interactions in food webs.

A highly host plant–specific weed biocontrol agent, the tephritid fly, Mesoclanis polana, introduced into Australia to control bitou bush, is associated with declines of local insect communities. As the agent shares natural enemies (predators and parasitoids) with seed herbivore species from native plants, a study implicated locally significant competition causing negative effects on indigenous seed feeding insects.

  • Conflicts of interest.
South western willow flycatcher

The endangered south-western willow flycatcher, using an invasive species (Tamarix sp.) for nesting sites in the USA.

The proposed biological control programme for saltcedars (Tamarix spp.) in North America is associated with concern about the wellbeing of an endangered species—the south-western willow flycatcher. Originally this bird species nested in indigenous riparian vegetation. Many western riparian areas are now dominated by introduced invasive saltcedars, which the south-western willow flycatchers are now using for nesting.




Post Release Evaluation – necessary but expensive

Post release evaluation is expensive, and requires long-term funding commitments and community support. Modern biocontrol practices recognize the need for post-release evaluation of biocontrol programmes, but in the past it has been seen as ‘an expensive luxury’! This is because evaluation is often perceived as basic research with no additional benefits to the community and the funding agencies. When a project has clearly been highly successful it is unappealing to channel further resources into a former problem when so many others still require attention. Likewise, if a project appears to have failed there is little incentive to spend precious resources documenting this in more detail.

The cost of undertaking Post Release Evaluation studies has to date proven to be a major obstacle both in New Zealand and worldwide. In 2015, the National Biocontrol Collective (NBC), the major funder of the development and release of new weed biocontrol agents in New Zealand, accepted a National Assessment Protocol developed by Landcare Research to ensure some level of assessment is undertaken in biocontrol projects in New Zealand. The protocol outlines minimum standards plus further options where additional resources are available.

Role of Post-Graduate Research Programmes

This is where Universities and their post-graduate research programmes can and are making major contributions, as evaluation studies are often incorporated into their research programmes. We as post graduate students (low-paid but reasonably intelligent – or just amazing supervisors?) can indulge in detailed population and ecosystem level studies – the ultimate goal of post release evaluation. Student cartoon


My Research

Neolema adult

The focus of my study: Neolema ogloblini, a biocontrol agent for Tradescantia fluminensis


My PHD study focusses on the dynamics of small populations. Many species benefit from the presence of conspecifics but at low population densities the fitness level of individuals in the population decrease. This phenomenon is known as the Allee effect. The Allee effect can drive very small populations to extinction and can play a major role in the establishment and spread of biocontrol agent populations.

I am studying how population size, dispersal and host patch connectivity interact with the Allee effect and how this influences the establishment and persistence of the leaf feeding beetle, Neolema ogloblini, a biocontrol agent for Tradescantia fluminensis. As mentioned in the introduction paragraph, 36 % of the biocontrol programmes in NZ has negligible benefit, in many cases because of establishment failure. My studies will help us to understand why some releases of biocontrol agents result in successful establishment and why others fail to do so.



Hester WilliamsHester Williams is a PhD candidate in the School of Biological Sciences, University of Auckland and is stationed with the Landcare Research Biocontrol team in Lincoln, Canterbury. She is interested in invasion processes of both insect and plant species. Hester is supervised by Darren Ward (Landcare Research/University of Auckland) and Eckehard Brockerhoff (Scion), with Mandy Barron (Landcare Research) as advisor. Her studies are supported by a joint Ministry for Primary Industries – University of Auckland scholarship. The project is an integral part of an MBIE program “A Toolkit for the Urban Battlefield” led by Scion.



The good old days of splattered bugs on windscreens

Posted by: Jessica Devitt @Colette_Keeha

Recently, a colleague of mine asked: “Have you noticed that there are less insects squashed on your car windscreen these days?” And I thought about it, and yes, there are definitely less bugs on my windscreen after a long drive now, as compared to when I was younger.

As a child, my family used to regularly drive across the North Island of New Zealand, from Wellington to Auckland and back, and I do distinctly remember there being numerous splattered insect remains on the car windscreen; and I remember mum or dad cleaning the insects off at the gas station, with the windscreen steadily becoming re-splattered within another hour or so of driving.


The reason my colleague brought up this issue was due to an article published in The Telegraph, which discusses the aptly named ‘windscreen phenomenon’.  The Telegraph article follows on from an earlier article published in Science News, and Radio New Zealand also covered the story here.  The jury is still out as to whether this is a sign of actual insect decline, or perhaps it is a result of other factors, such as the more streamlined modern car.

The windscreen (or windshield) phenomenon was coined by entomologists to define the relatively recent apparent lack of insects inadvertently colliding with car windscreens during transit.  This is purely observational, but it does correlate with recorded decreases in pollinators, and other more charismatic insect species albeit still pollinators, such as butterflies.

This got me thinking about the insects that I saw regularly, and captured, as a kid – have I seen that particular species recently?  When was the last time I saw it?  And does that necessarily mean they are declining just because I haven’t seen them?  This exercise for me is purely speculative and observational, however, I thought it would be interesting to research a couple of the insects that I haven’t seen much of, and then see if there is any information on how they are faring these days. Maybe they have experienced some population decline or range restriction…or perhaps I just need to look a little harder!

1). Native praying mantis (Orthodera novaezealandiae)


 Female New Zealand Mantis (Orthodera novaezealandiae) from side. (McQuillan, 2009.)


Left: Native female New Zealand Mantis (Lee, 2017). Right: Female South African Mantis (Lee, 2017)

Now this one I know is recorded as declining (Buckley et al., 2012).  I haven’t seen one of these guys for ages, but I do remember seeing them fairly consistently circa late 80’s early 90’s in suburban Auckland.  It is thought that the decline of the native mantis is due to competition with the introduced South African mantis (Miomantis caffra).  Further, the native male mantis has been found to be attracted to the South African female mantis, for which he tries to mate with and is invariably eaten.

Conclusion: Declining


2) Striped flower fly (Orthoprosopa bilineata)


Orthoprosopa bilineata (Bundle, 2015)


Coming across one of these was a rare find, maybe I saw one a handful of times over a year but at this point I have not come across one for a very long time!  I see on Nature Watch they are still being sighted in the Auckland area, but there is not much information about them online. Something I did learn was that this species is only found in New Zealand.

Conclusion: Look harder?


3) Emperor gum moth (Opodiphthera eucalypti)



Top: Emperor Gum Moth, Opodiphthera eucalypti, female; Swifts Creek, Victoria (fir0002 /, 2007).
Bottom: The caterpillar of the emperor gum moth in its last stage before pupation (Fir0002, 2005).

This is not a native species to New Zealand but a favourite of mine as a kid.  It is originally from Australia and its most common host plants are within the eucalypt family, leading to the moth being considered a pest for commercial eucalypt growers.  I do actively look for them when I come across any eucalyptus trees but have not seen one for a few decades now.  However, they are still considered common.

Conclusion: Look harder

This exercise was probably more of an excuse for me to reminisce about carefree bug-catching days, whilst I work like crazy to grow as many beetles as possible for future experiments.  However, I do think it is important that we take the time to notice the natural environment around us – what are we seeing lot of?  What have we not seen for a long time?  Are we noticing the emergence of certain species of flora or fauna at different times of the year than what we would normally expect?  These sorts of observations can lead to future projects that may highlight population level changes, changes in species distribution, changes in behaviours and/or growth patterns, and at the very least provide more information on often overlooked less charismatic data deficient individuals.

jessJessica Devitt is a PhD student at the Centre for Biodiversity & Biosecurity, School of Biological Sciences, University of Auckland and Plant and Food Research. She is researching the respiratory responses of the golden-haired bark beetle to advance fumigation techniques. She is supervised by Jacqueline Beggs from the University of Auckland, Adriana Najar-Rodriguez and Matthew Hall from Plant and Food Research.



Buckley, T. R., Palma, R. L., Johns, P. M., Gleeson, D. M., Heath, A. C. G., Hitchmough, R. A., & Stringer, I. A. N. (2012). The conservation status of small or less well known groups of New Zealand terrestrial invertebrates. New Zealand Entomologist, 35(2), 137-143.

Bundle, P. (2015).  Orthoprosopa bilineata. Retrieved from

fir0002 / (2007). Emperor Gum Moth, Opodiphthera eucalypti, female; Swifts Creek, Victoria. Retrieved from

fir0002. (2005). The caterpillar of the emperor gum moth in its last stage before pupation.  Retrieved from

Lee, S. (2017).  Praying mantis identification.  Retrieved from

McQuillan, B. (2009). Female New Zealand Mantis (Orthodera novaezealandiae) from side.  Retrieved from