The samurai wasp (Trissolcus japonicus) is a tiny parasitoid that attacks the eggs of the brown marmorated stink bug (Halyomorpha halys), a notorious pest that damages fruit and vegetable crops around the world.
The wasp lays its eggs inside the stink bug eggs, killing them and producing more wasps.
The samurai wasp is native to Asia, where it co-evolved with the stink bug and helps to keep its population in check.
The samurai wasp has been introduced or detected in several countries where the stink bug has invaded, such as the United States, Canada, Switzerland, Italy, and Germany.
It is considered a promising biological control agent that can reduce stink bug damage and pesticide use.
However, there are also concerns about its potential impact on native stink bugs that are not pests and may have ecological or economic value.
A new study led by CABI has investigated the host range and specificity of the samurai wasp in Europe, where it has been accidentally or intentionally released in recent years.
The study aimed to assess how likely the wasp is to attack and parasitize native stink bugs in the field, and what factors may influence its host selection.
The methods and results of the study
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The study, published in the Journal of Pest Science, involved exposing sentinel egg masses of the stink bug and 18 non-target species to the samurai wasp in Switzerland and Italy over three years, as per Phys.org.
The researchers also collected naturally laid egg masses from different habitats and locations.
They then analyzed the parasitism rates and patterns of each species by the wasp using molecular and morphological methods.
The results showed that the samurai wasp has a broad fundamental host range, meaning that it can successfully parasitize many species of stink bugs under laboratory conditions.
In fact, 15 of 18 non-target species were parasitized by the wasp in the field.
However, most non-target species were less parasitized than the stink bug, suggesting that they have partial temporal or spatial refuges from the wasp attack.
The researchers found that the realized host range of the samurai wasp, meaning the actual hosts that it attacks and parasitizes in nature, depends on several factors, such as:
The availability and abundance of hosts. The wasp tends to prefer hosts that are more common and accessible in its environment.
The phenology and life cycle of hosts. The wasp tends to prefer hosts that lay their eggs at the same time as the stink bug or later in the season when its population is higher.
The ecological niche and habitat of hosts. The wasp tends to prefer hosts that share similar habitats and resources with the stink bug, such as fruit trees or crops.
The phylogenetic relatedness of hosts. The wasp tends to prefer hosts that are more closely related to the stink bug, such as other members of the Pentatomidae family.
The implications and recommendations for conservation and management
The study confirmed that the samurai wasp has minimal impact on native stink bugs in Europe, as it mainly targets its primary host, the stink bug, as per CABI News.
However, it also revealed that some non-target species may face an increased risk of parasitism by the wasp, especially those that have an unusual life cycle or occupy the same ecological niche as the stink bug.
For example, Pentatoma rufipes, a native species that feed on fruits and seeds, was the most parasitized non-target species in both countries.
The researchers recommend that more studies be done to evaluate the impact of non-target parasitism on the population dynamics and fitness of native stink bugs.
They also suggest that more monitoring and surveillance be done to track the distribution and abundance of both the samurai wasp and its hosts across different regions and habitats.
They also urge caution and coordination when releasing or managing the samurai wasp, as it may have different effects in different contexts.
The samurai wasp is a valuable ally in the fight against the stink bug, but it is not a silver bullet.
It is important to consider its potential benefits and risks for the native biodiversity and ecosystem services and to adopt an integrated pest management approach that combines biological, cultural, and chemical methods.
