Comparing the host-specificity of two Tuta absoluta parasitoids from different origin

Abstract: New strategies are urgently needed to control Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), one of the most destructive pests of tomato crops. Originating from South America, it has a high reproduction capacity and has evolved resistance to most common insecticides making its control very challenging. The parasitoid Necremnus tutae (Reuter) (Hymenoptera: Eulophidae) is widely present around the Mediterranean and has adapted to the invader playing a substantial role in its natural control. The neotropical parasitoid Dolichogenidea gelechiidivoris Marsch (Hymenoptera: Braconidae) has recently established following its host into Spain and Algeria. Evaluating the host-specificity of the two parasitoids for the target host T. absoluta is essential to assess their value as augmentative or classical biological control agents. We conducted host-specificity tests in the laboratory offering four European leafminer species in no-choice and choice setups. We tested, as a closely related species from the same family as T. absoluta, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae); as lepidopteran leafminers from two different families, the horse chestnut leafminer Cameraria ohridella Deschka & Dimic (Lepidoptera: Gracillariidae) and the pear blister leaf miner Leucoptera malifoliella Costa (Lepidoptera: Lyonetiidae); and as a leafminer from another order but feeding on tomato, Liriomyza bryoniae (Kaltenbach) (Diptera: Agromyzidae). We then assessed the realized host range in the field by exposing sentinel plants containing the target host T. absoluta or the nontarget host P. operculella, inside Spanish greenhouses where both parasitoids were present. In parallel, we assessed each parasitoid species’ field parasitism rate. Our results show that, in the laboratory, out of four nontarget species tested, N. tutae showed no preferences between T. absoluta and the three Lepidoptera species, while D. gelechiidivoris demonstrated a strong affinity for T. absoluta and P. operculella. In the field, N. tutae showed no preference between the target and P. operculella, whereas D. gelechiidivoris parasitized the T. absoluta twice as often as the nontarget host P. operculella. The mean T. absoluta parasitism rate reached 27 % for N. tutae and 35 % for D. gelechiidivoris. Overall, N. tutae seems highly polyphagous, attacking various lepidopteran species, whereas D. gelechiidivoris seems specific to Lepidoptera of the Gelechiidae family