Fundamental host range of Trissolcus japonicus in Europe

Abstract

The brown marmorated stink bug, Halyomorpha halys, native to East Asia, is an invasive alien pest that arrived in Europe in the early 2000s and poses an imminent threat to a wide variety of crops. Adventive populations of the Asian egg parasitoid Trissolcus japonicus, the most promising agent for classical biological control of H. halys, have recently been detected in Italy and Switzerland. Its prospective fundamental host range in Europe was evaluated in behavioural no-choice tests, followed by large-arena choice tests presenting host plants with naturally laid egg masses of target and non-target hosts. Developmental suitability of European non-target host species for T. japonicus was demonstrated, via no-choice tests, by offspring emergence (successful parasitism) from eleven out of thirteen non-target species tested (85%). Whereas successful parasitism of most non-target species was significantly lower, acceptance of Arma custos, Palomena prasina, Pentatoma rufipes, and Rhaphigaster nebulosa was not significantly different from H. halys controls. When eggs of H. halys and non-target species were exposed in a semi-natural situation in large-arena choice tests, the degree of non-target parasitism was substantially reduced for three out of four tested species, whereas parasitism of Pa. prasina eggs was not. It remains unclear if there are behavioural barriers to parasitism that may exist and preclude excessive parasitism of potentially threatened species in the field, but field data from the invaded areas in Switzerland and Italy could contribute to a risk-benefit evaluation of releasing or relocating adventive T. japonicus populations into other parts of Europe. Keywords Biological control • Egg parasitoids • Non-target effects • Risk assessment • Halyomorpha halys Key message • The Asian egg parasitoid Trissolcus japonicus, the main antagonist of the invasive Halyomorpha halys, was recently discovered in Europe (i.e. Italy and Switzerland). • We investigated its fundamental host range in Europe in behavioural no-choice and large-arena choice experiments. • In no-choice tests, eleven out of thirteen non-target species were suitable for development and acceptance of four species was not significantly different from H. halys. • In choice tests, non-target parasitism was substantially reduced for three out of four tested species. • Field data from the invaded areas in Europe could contribute to a risk-benefit evaluation of releasing or relocating adventive T. japonicus populations. Communicated by M. Traugott.

An Insight into the Role of Trissolcus mitsukurii as Biological Control Agent of Halyomorpha halys in Northeastern Italy

“…Some of these stink bugs are very common in northern Italy [59,60], where T. mitsukurii is likely to attack their eggs. Thus, although T. japonicus's fundamental host range has been already investigated [61][62][63], similar studies are needed for T. mitsukurii.…”

Current distribution and voltinism of the brown marmorated stink bug, Halyomorpha halys, in Switzerland and its response to climate change using a high-resolution CLIMEX model

“…Currently, there are no sufficient tools available for managing H. halys in Switzerland, but a very promising and sustainable approach could be the use of exotic natural enemies. The Asian samurai wasp, Trissolcus japonicus (Hymenoptera: Scelinoidae), has been identified as the most promising classical biological control agent in Asia and adventive populations were recently found in the Switzerland and Italy (Haye et al 2020;Moraglio et al 2020;Sabbatini Peverieri et al 2018;Stahl et al 2019). It remains unknown though, which areas will be most suitable for the establishment of the parasitoid in Switzerland and how climate change may alter its distribution.…”

Hidden Host Mortality from an Introduced Parasitoid: Conventional and Molecular Evaluation of Non-Target Risk

“…In fact, laboratory host range studies on a closely related species, Nezara viridula (both species are in the tribe Nezarini), found similar levels of unemerged nymphs (approx. 50%) in egg masses that were exposed to T. japonicus [ 43 , 44 ], and unexposed, control egg masses of Nezara viridula also had approximately 50% unemerged eggs [ 44 , 45 ], indicating that the high levels of mortality in this group may be unrelated to parasitoid exposure. However, unemerged eggs could also, at least in principle, be as a result of unsuccessful oviposition by a parasitoid (i.e., probing) that does not leave DNA evidence.…”

“…However, unemerged eggs could also, at least in principle, be as a result of unsuccessful oviposition by a parasitoid (i.e., probing) that does not leave DNA evidence. Laboratory studies have shown that some members in the tribe Nezarini are poor reproductive hosts for T. japonicus [ 20 , 43 , 44 , 45 ], and higher levels of unexplained mortality in T. japonicus -exposed versus unexposed eggs have been observed in some studies [ 45 ]. The detection of parasitoid DNA from probing without oviposition has not been tested but is unlikely to result in detectable levels of parasitoid DNA unless other substances (e.g., venom, arrestment factors) are injected by the female parasitoid.…”

“…In future studies it would also be prudent to expose control egg masses to the same environmental field conditions in a way that excludes parasitoid access to the egg mass (i.e., using fine mesh cages or sleeves) to provide a more accurate assessment of natural mortality. In addition to significantly higher mortality levels, laboratory studies by Haye et al [ 45 ] also observed a significantly longer handling time of N. viridula egg masses in comparison to H. halys , even when egg mass size was controlled. It would be interesting to determine whether this also occurs in Chinavia (and other Nezarini) and whether increased probing is correlated with higher host mortality.…”