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

Abstract

In crop systems, successful management of invasive insect herbivores can be achieved through the introduction of exotic biocontrol agents, parasitoids or predators, having a coevolutionary history with the pest. To avert threats to local biodiversity, recent legislations require a risk assessment for the organism to be released. Evaluation of its ability to exploit, for host location, odours associated with target and non-target species is crucial for a better definition of its ecological host range. Using Y-tube olfactometer bioassays in a quarantine laboratory, we investigated the ability of the Asian egg parasitoid Trissolcus mitsukurii (Hymenoptera: Scelionidae) to exploit odours associated with the global invader Halyomorpha halys (Hemiptera: Pentatomidae) and with non-target stink bugs native to Southern Europe. We demonstrated that T. mitsukurii is attracted by plants exposed to feeding and egg deposition of the coevolved H. halys and the native Nezara viridula, while it is not attracted by physogastric (gravid) females or eggs alone. Remarkably, T. mitsukurii is repelled by plants bearing eggs of the beneficial Arma custos. Our results contribute to a more thorough and nuanced assessment of the potential non-target risks in the case of mass-release of parasitoids as part of a biological control programme for invasive stink bugs.

Attraction of Egg Parasitoids Trissolcus mitsukurii and Trissolcus japonicus to the chemical cues of Halyomorpha halys and Nezara viridula

“…This detail could presume the existence of some sort of co-evolutionary or adaptation process. A recent survey on the olfactory response of T. mitsukurii confirms this inclination for N. viridula [ 42 ]. Indeed, the parasitoid manifested an interest in the arm containing a plant contaminated by N. viridula , which was previously exposed to individuals for feeding and oviposition [ 42 ].…”

“…Conversely, BMSB cues elicited a modification in the kinetic reaction with a reduced intensity. The aforementioned interest was confirmed in olfactory investigation [ 42 ], while discordant results were highlighted in the physiological host range [ 43 ]. Additional analyses are needed to prove this preference.…”

Tritrophic analysis of the prospective biological control of brown marmorated stink bug, Halyomorpha halys, under extant weather and climate change

“…Bertoldi et al (2019) found a strong preference in T. japonicus for olfactory cues of its putative coevolved BMSB host, even when it emerged from other species (Boyle et al 2020). In northern Italy, adventive populations of T. mitsukurii also display a strong preference for BMSB (Rondoni et al 2022).…”

No adverse effects of symbiotic control on the parasitism of Halyomorpha halys by egg parasitoids

“…In contrast, T. mitsukurii showed significantly lower emergence percentages in egg masses treated with Dentamet ® , despite the high proportion of parasitized eggs (> 81%) for all treatments. Since the exposure to H. halys egg masses in the absence of the host plant was reported to be inefficient in attracting this wasp (Rondoni et al 2022), the odour blend emitted after treatment with Dentamet ® may further impair the wasp recognition of the host eggs, at least in our experimental conditions, where no plant was offered to the wasp. The elimination of P. carbekii may interfere with the attraction exerted by some symbiont-derived volatiles; the interference with attraction for volatiles may be exacerbated by the general non-preference of T. mitsukurii for wet eggs, as evidenced by the untreated vs treated with water paired choice test.…”