Samurai wasp to combat the brown marmorated stink bug

In recent years the brown marmorated stink bug (Halyomorpha halys) has spread to many parts of Europe. Originally from Asia, since 2016 the bug has been present in South Tyrol, where it has caused damage to a number of agricultural crops and could well wreak havoc in the fruit industry. 
Minor damage was first reported in South Tyrol in 2018, and the estimated total loss last year was somewhere in the region of 20 million euros. 

Scientists at the Laimburg Research Centre in South Tyrol (Italy) have been researching the Halyomorpha halys since 2016. “In order to develop a feasible strategy to combat the presence of this bug, previously unknown here, we first have to understand its behaviour patterns and biology,” explains Klaus Marschall, Director of the Institute for Plant Health at the Laimburg Research Centre. Experts at the centre are currently testing and developing a number of measures to combat the bug population, and are exchanging findings with local, national and international Research and Advisory institutions. 

Image sources: Laimburg Research Centre

Measures to control the brown marmorated stink bug 

Having gained an understanding of the behaviour patterns of the bug, the next step taken by the Institute for Plant Health was to trial a serious of regulation measures. To date, efforts to control the presence of the brown marmorated stink bug in South Tyrol and other affected regions have been based on the application of chemical insecticides and insect-proof netting. In the long term however, sustainable strategies such as biological control through the use of a natural enemy would provide a more desirable solution. In Asia, the brown marmorated stink bug is kept in check by natural means, namely by specific parasitoids such as the samurai wasp (Trissolcus japonicus). In the future, this “natural antagonist” native to the original distribution area of the Halyomorpha halys may well also be used in South Tyrol to reduce the population density of the marmorated stink bug to the extent that it no longer poses a threat to native crops. ”Initial laboratory tests carried out in Switzerland, China and the USA demonstrate that the samurai wasp can parasitise 90 to 100 % of the eggs of the marmorated stink bug,” reports entomologist Silvia Schmidt.

First samurai wasps found in Switzerland

Research conducted in apple orchards in the Swiss canton of Tessin led to the discovery of samurai wasps originating from egg clutches of the marmorated stink bug. “It is difficult to say for certain how the samurai wasp arrived in Switzerland - it was probably accidentally transported from its native range along with the pest,” explains Tim Haye from the Cabi Research Institute in Delberg (Switzerland). “But whether Switzerland was the actual country of introduction or whether the wasp was introduced into the climatically highly-suitable northern Italy before spreading northwards remains unclear.”

Breeding and release of the samurai wasp 

Breeding of the samurai wasp is essential in order to guarantee its effectiveness as a natural antagonist. Lab trials to date will be progress to the outdoors in summer 2020. Naturally, great caution is fundamental during this phase as the release of a non-native species into the wild can have a detrimental impact on the local ecosystem. IN consideration of this risk, Italy’s Department for Environment has carried out exhaustive examination and assessment of all potential consequences. A decree signed by the President of the Republic in September 2019 (No. 102, July 5th 2019) allows for the introduction of non-native species and the use thereof in pest control. A further decree issued by the Department for Environment on April 2nd 2020 established criteria governing the release of non-native species such as the samurai wasp.

“The samurai wasp is a small, egg-eating parasitoid, roughly 2 mm in length, which parasitises the egg clutches of the brown marmorated stink bug. It lays its eggs in each egg of the stink bug clusters, thus preventing them from multiplying,” explains Martina Falagiarda from the Entomology work group of the Laimburg Research Centre in South Tyrol. 

In order to release the samurai wasp successfully and promote its integration in South Tyrol, the insect must be bred. This has been legally permitted in Italy since May 2020, and is coordinated by the national research institute CREA (Council for Agricultural Research). CREA have now been commissioned by the National Plant Protection Service to supply authorised regional research institutions with material for the reproduction of the samurai wasp. In the Autonomous Province of Bolzano, South Tyrol, the Laimburg Research Centre has been commissioned to breed the samurai wasp for the biological regulation of the brown marmorated stink bug and, in the neighbouring region of Trentino, the Edmund March Foundation in San Michele all’Adige. 
The samurai wasp was recently released in 42 locations to encourage its integration in South Tyrol and enable sustainable regulation of the brown marmorated stink bug.  

Native parasitic wasp control already underway

A further step in the fight against the marmorated stink bug can be found in the form of another natural antagonist: the Anastatus bifasciatus, a domestic parasitic wasp already present in South Tyrol; however, in order to maximise its efficiency as an antagonist of the marmorated stink bug, its reproduction must be assisted. It has been propagated in the laboratories of Bioplanet from Cesena and has recently been released in a number of locations in South Tyrol. When the first colonies were released in Nals, Stefano Foschi, spokesman for the lab, emphasised that this parasitic wasp poses no threat to humans, animals or the environment, particularly so as it is a naturally-occurring species in South Tyrol. “Quite the reverse: its proliferation is a natural compensation of the ecological balance.” 

The development of this joint project of the South Tyrol Apple Consortium, the AGRIOS work-group for integrated cultivation, the South Tyrolean Advisory Service for Fruit Production and Wine Growing and the Laimburg Research Centre will be closely monitored in the coming weeks to monitor the success that is hoped for in the release of these parasitic wasps.

Future containment of the brown marmorated stink bug 

The extent to which the samurai wasp can live up to its name and the impact of the domestic parasitic wasp may provide a significant contribution to combatting the brown marmorated stink bug. Given that the application of chemical insecticides and exclusion netting have not been a significant source of success to date, these new findings, trial schemes, and the controlled breeding of the samurai wasp certainly give us hope for future containment of  the damage that the brown marmorated stink bug wreaks upon apple and other fruit crops. 

Sources

Laimburg Research Centre

Cordis (EU research findings)

South Tyrol Apple Consortium