Lethal and sub-lethal effects of fungicides and plant strengtheners on Trissolcus japonicus and Trissolcus mitsukurii, egg parasitoids of Halyomorpha halys

The widespread use of fungicides in fruit orchards can represent a potential threat to the natural enemies of a major pest of fruit crops, the invasive brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae). Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae) and Trissolcus mitsukurii (Ashmead) (Hymenoptera: Scelionidae) are two egg parasitoids of H. halys that were recently detected in invaded areas. Trissolcus japonicus is currently being utilized in classical biological control programmes in several regions. The lethal and sub-lethal effects on longevity, parasitism and behaviour of fungicides (sulphur, copper oxychloride, potassium hydrogencarbonate, calcium polysulfide, dithianon, captan, dodine) and plant strengtheners (kaolin, zeolite) commonly sprayed in fruit orchards were investigated on T. japonicus and T. mitsukurii in laboratory conditions. Parasitoids adults were exposed to fresh dry residue on inert material on the same day of the treatment, typically 2-3 h after application. The exposure to kaolin caused the highest mortality to both T. japonicus and T. mitsukurii, while no lethal effects were observed for all other products investigated. Nevertheless, the longevity of T. mitsukurii was reduced by the exposure to all products investigated, and a reduction of the survival probability was also observed for T. japonicus except when exposed to sulphur. Fecundity of females exposed to dry residues was not compromised, while egg parasitism and parasitoid emergence from treated H. halys egg masses were reduced by all products. In detail, calcium polysulfide had the most detrimental effect on both parasitoid species, affecting both the parasitism rate and offspring emergence from treated egg masses. In the behavioural trial, both T. japonicus and T. mitsukurii showed a preference for avoiding contact with sulphur and potassium hydrogencarbonate dry residues. Overall, combining lethal and sublethal effects together, kaolin resulted harmful to T. mitsukurii and moderately harmful to T. japonicus, while calcium polysulfide resulted moderately harmful to both Trissolcus. All the other products resulted slightly harmful, and none resulted harmless to both parasitoids.