Physiological Host Range of Trissolcus Mitsukurii, A Candidate Biological Control Agent of Halyomorpha Halys

Abstract

The invasive stink bug Halyomorpha halys is a severe agricultural pest of worldwide importance, and chemical insecticides are largely sprayed for the control of its populations. Negative impacts and several failures in chemical pest management led to consider classical biological control as one of the most promising methods in a long-term perspective. The Asian egg parasitoid Trissolcus japonicus is the main candidate biocontrol agent of H. halys, but more recently a second Asian egg parasitoid, Trissolcus mitsukurii, is getting attention after adventive populations were found on H. halys egg masses in Europe. Before recommending the use of T. mitsukurii for biological control of H. halys, a risk analysis is necessary and therefore here we present the first study on the fundamental physiological host range of this parasitoid in Europe. Tests conducted with T. mitsukurii on different hemipterans, using three different experimental designs, revealed a broad physiological host range, comparable with the host range displayed by T. japonicus under similar laboratory conditions. Specifically, in addition to its coevolved host H. halys, T. mitsukurii successfully parasitized the majority of tested pentatomid species and one scutellerid, although with highly variable emergence rates. Host egg sizes positively affected parasitoid size and female egg load. Further studies, testing more complex systems that involve olfactory cues from host and host plants, will simulate different aspects of the parasitoid host location behavior under field conditions, allowing in-depth evaluation of the possible risks associated with the use of T. mitsukurii as a biocontrol agent of H. halys.

Olfactory responses of Trissolcus mitsukurii to plants attacked by target and non-target stink bugs suggest low risk for biological control

“…Previous choice and no-choice bioassays underlined high acceptance and suitability of D. baccarum for T. mitsukurii (Giovannini et al 2021). Surprisingly, our data did not reveal any behavioural response of this parasitoid to odours from soybean plants bearing egg masses of D. baccarum.…”

“…Indeed, the parasitoid is considered a main enemy of N. viridula in Japanese areas where the stink bug has established (Hoyko et al 1996;Arakawa et al 2004). Surprisingly, despite this remarked discovery ability, the emergence rate displayed by T. mitsukurii was null or very low, in the case of the adventive Italian population (Scaccini et al 2020;Giovannini et al 2021), and moderate (e.g., ~40%) for Japanese strains (Kiritani and Hôkyo 1962;Hokyo et al 1966). This mismatch between the positive response of T. mitsukurii to cues associated with N. viridula and the low suitability of this host for parasitoid development is partially consistent with lack of coevolution, as N. viridula is of Ethiopian-South Mediterranean origin (Vinson 1975;Esquivel et al 2018;Konopka et al 2018).…”

“…In no-choice black box experiments, E. ventralis eggs represented a poorly suitable host for T. mitsukurii, as parasitoids failed to develop inside its eggs (Giovannini et al 2021). The lack of response towards odours from plants bearing an egg mass of E. ventralis in our experiments is consistent with the very low suitability of this species (Giovannini et al 2021). The stink bug is of Paleartic origin and is only marginally present in the native area of T. mitsukurii (Rider et al 2002;Rider 2006;Giovannini et al 2021).…”

“…A detailed screening of T. mitsukurii host range using choice and no-choice Petri dish experiments was conducted previously and revealed oligophagy of this parasitoid limited to members of the Pentatomoidea superfamily (Giovannini et al 2021). However, the capability of this parasitoid to exploit odours from the plant-host system for locating stink bug eggs in the eld is unknown.…”

“…are primarily attracted by oviposition-induced plant synomones (Colazza et al 2004;Conti et al 2010;Tognon et al 2016;Borges and Blassioli-Moraes 2017;Bertoldi et al 2019). Here we hypothesized that the oligophagous behaviour shown by T. mitsukurii during assessment of its physiological host range (Giovannini et al 2021) would result narrower if the chemical ecology of this parasitoid is investigated. Speci cally, only odours associated with those host species that exhibit coevolutionary history with T. mitsukurii would elicit behavioural responses of the parasitoid.…”