AWA: Academic Writing at Auckland

Policy Submission Macrolophus pygmaeus

There are three major factors that can be used to indicate if a species is able to become invasive in a given ecosystem and they are climate compatibility, nutrient availability and propagule pressure. There is evidence to suggest that all three of these factors in the New Zealand context could be potentially suitable for the establishment and invasion of Macrolophus pygmaeus. There is a gross lack of research into New Zealand specific species and climate interaction on M. pygmaeus to prove its unlikeness to establish, spread and have minimal impact on New Zealand species through predation and competition. Thus we are opposing this application for the controlled introduction of Macrolophus pygmaeus for biological pest control as the risks at this stage are deemed too high.

Potential for M. pygmaeus to establish outside the greenhouse:

Climate suitability

Macrolophus pygmaeus is a tropical species that thrives in warm temperatures (Perdikis & Lykouressis, 2000), but CLIMEX model data by Logan et al. (2012) indicates that there is a high likelihood of M. pygmaeus being able to find suitable climates in various areas of the North Island.  The application for release emphasises another study with Maxent and Multimodal software that found establishment highly unlikely and limited to a small area of Kaitia (Logan, 2013). However, this is a false representation of the data as the report itself stated that, with a sample number of only 23 there is a high probability of a coincidental correlation, and that the CLIMEX model is more reliable (Logan et al, 2012). Further support of this comes from two studies in the UK that looked at survival of Macrolophus calliginosus (a closely related species to M. pygmaeus) outside of the greenhouse (Hart et al., 2002; Hatherly et al., 2005). They found, with access to suitable quantities of prey, M. pygmaeus is capable of surviving through most of the colder temperatures of winter (and does so in some recorded instances in the UK).

It is stated in the application that this species was already introduced to Auckland and failed to establish outside of the greenhouse thus proving inability to survive the climate. However this claim also does not take into account the large propagule pressure they are proposing. Propagule pressure is a major indicator of species establishment, and regular annual release of M. pygmaeus that they have indicated in their proposal will increases this risk significantly (Hart et al., 2002; Stow et al., 2015). The period of prior introduction from 2007-2009 is not sufficient evidence to claim that M. pygmaeus is unable to survive outside the greenhouse as it has not shown the effects over large scale recurrent propagule pressure.

Nutrient availability

Multiple studies show prey availability is a strong factor in M. pygmaeus survival and reproduction (Put, 2012; Hart et al., 2002). Macrolophus pygmaeus is a generalist species that can prey on a wide variety of both invertebrates and plants. This makes prediction of their niche difficult to determine as there are many options open to them.  Their diet is known to consist of thrips, aphids, mites, leaf miners, a few lepidopteran species eggs, tomatoes, tobacco and other plants  (Ingegno, 2011; Vandekerkhove et al., 2011) of which NZ has over 1600 native varieties as stated in the application (section 6.3.1). The applicant indicates that their preference is for Whitefly but studies have shown thier preference depends on prey density levels rather than species type (Enkegaard et al., 2001; Jaworski et al., 2013).

Vandekerkhove and De Clercq (2010) found the optimal diet is around 40 lepidopteran eggs for development and reproduction but they can survive on less with the supplementation of pollen. They are capable of surviving on 100% plant diets whilst still reaching full maturity(Perdikis & Lykouressis, 2000; Hart et al., 2002). They can also survive on carnivorous diets over multiple generations without any effects on their generalist behaviour or prey/plant preferences (Castañé & Zapata, 2005; Vandekerkhove et al., 2011).

With a diet this general, Macrolophus pygmaeus release is of great concern because New Zealand has a very wide variety of invertebrate species including many endemic that fit this range. This species has a high risk factor for switching to native NZ species and until this has been properly tested we can not accurately predict the extent of dietary range of this species.

Potential for M. pygmaeus to spread:

The hardest part of invasion is overcoming initial arrival and establishing. Intentional introduced species bypass this phase (Stow et al., 2015). The greenhouse environment would provide an ideal nursery for this species and assuming that no individuals will leave this environment is unrealistic (Blitzer et al., 2012). Poor greenhouse management, overpopulation and prey scarcity are all potential reasons M. pygmaeus might involuntarily disperse. On the other side, favourable climate through the summer (Hart et al., 2002; Logan et al., 2012), and prey/pollen availability may cause voluntary dispersal (Put et al., 2012). Their abundance, and spread is strongly associated with prey abundance and location, and we could expect that should they secure large sources of alternative prey they will naturally spread from the greenhouses (Put, 2012). Over the few winter months in the year that the climate would be unfavourable there are a multitude of microclimates that could shelter M. pygmaeus including the greenhouses, buildings, and farm sheds, assisting in its survival and spread (Hart et al., 2002).

Potential impact:

The range of M. pygmaeus has the potential to be wide across the North Island with many dietary niche options and favourable climate available (Ingegno, 2011; Logan, 2012). There are also a few established plant species as well as a range of crop varieties across the North Island that could provide shelter and supplementary feeding (section 6.3.2). Another potential host species not mentioned in the application is Woolly Nightshade (Solanum mauritianum) which has the hairy leaf qualities preferred by M. pygmaeus as stated in the application (McGregor, 1999). This is a highly invasive weed that could provide a dispersal medium throughout the North Island (McGregor, 1999).

Macrolophus pygmaeus is found to take 1-2 weeks to reach useful population levels for biocontrol on European crops, or longer if it is surviving on a host plant alone (Castañé et al., 2006a; Lenfant et al., 2000; Put, 2012). Its propagation is generally assisted by farmers providing extra egg feed to quicken reproduction (Put, 2012). In the UK studies on M. Calliginosus development from egg to adult took between 25 days at 26°C to 130 days at 11°C (Hart et al., 2002). From this we could infer the that M. pygmaeus once established could reach large population levels over the New Zealand summer, particularly in the far north and maintain smaller populations maturing at a slow rate over the winter.

The abundance of M. pygmaeus outside of greenhouses is the biggest concern as large infestations of M. pygmaeus spurred on by high prey density could have devastating effects on the native flora and fauna as well as other industry crops (Castañé et al., 2011).  M. pygmaeus is a generalist species which means there could be wide ranging implications that we just cant predict with the present state of research. The ongoing risks are that if this species establish and become invasive, eradication would be difficult and expensive due to its ability to adapt to different resources (Stow et al., 2015).

CONCLUSION

The most concerning thing about this application for M. pygmaeus introduction is that there has been insufficient testing of any native New Zealand species and their interactions with M. pygmaeus. The climate data supplied is misinterpreted and actually shows a range of North Island habitats for this species to survive in. Macrolophus pygmaeus is a generalist predator with the ability to prey on a wide variety of invertebrates as well as plants. So far the available international reasearch suggests this species displays a capacity for surviving on a multitude of NZ native species that could have any number of unforeseen impacts. The quantities that the tomato industry are proposing to bring in on an annual basis would be providing further propagule pressure to the mix which only increases this potential risk exponentially. We are opposing this application on these grounds and recommending that far more research is done on M. pygmaeus and its specific interactions with the New Zealand ecosystem before considering introduction for biocontrol.

References

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Castañé, C., Alomar, O., Riudavest, J., & Gemeno, C. (2006a). Reproductive traits of the generalist predator Macrolophus caliginosus. IOBC/WPRS Bulletin, 29, 229–234.

Castañé, C., Arnó, J., Gabarra, R., & Alomar, O. (2011). Plant damage to vegetable crops

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Castañé,  C.; &  Zapata, R. (2005). Rearing the predatory bug Macrolophus caliginosus on a meat-based diet. Biological Control, 34,66–72.

Enkegaard, A.; Brodsgaard, H.; & Hansen, D. (2001). Macrolophus caliginosus: Functional response to whiteflies and preference and switching capacity between whiteflies and spider mites. Entomologia Experimentalis Et Applicata, 101(1), 81-88. DOI: 10.1046/j.1570-7458.2001.00893.x.

Hart, A.; Tullett, A.; Bale, J.; &Walters, K. (2002). Effects of temperature on the establishment potential in the UK of the non-native glasshouse biocontrol agent Macrolophus caliginosus. Physiological Entomology, 27(2) 112-123. DOI: 10.1046/j.1365-3032.2002.00276.x.

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Ingegno, B.; Pansa, M.; & Tavella, L. (2011). Plant preference in the zoophytophagous generalist  predator Macrolophus pygmaeus (Heteroptera: Miridae). Biological Control. 58(3), 174-181.   DOI:10.1016/j.biocontrol.2011.06.003.

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Lenfant, C.; Ridray, G.; & Schoen, L. (2000). Biopropagation of Macrolophus caliginosus Wagner for a quicker establishment in Southern tomato greenhouses. Bulletin OILB SROP. 23, 247–251.

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McGregor, P. (1999). Prospects for biological control of Woolly Nightshade, Solanum mauritianum (Solanacea: Solanoideae). Landcare Research, Palmerston North. Landcare Research   Contract Report No.LC9900/035.

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Put, K.; Bollens, T.; Wäckers, F.; & Pekas A. (2012). Type and spatial distribution of food supplements impact population development and dispersal of the omnivore predator Macrolophus pygmaeus (Rambur) (Hemiptera: Miridae). Biological Control. 63, 172–180. http://dx.doi.org/10.1016/j.biocontrol.2012.06.011

Stow, A.; Maclean, N.; & Holwell, G. (2015) Austral ark [NetLibrary version]. Retrieved from http://hdl.handle.net/1959.14/345607

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Vandekerkhove, B.; & De Clercq, P.(2010). Pollen as an alternative or supplementary food for the mirid predator Macrolophus pygmaeus. Biological Control, 53, 238–242.