Insight into the host-specificity of a native and a newly introduced parasitoid of Tuta absoluta and prospect for biological control

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 is spreading rapidly and has evolved resistance to most common insecticides making it highly challenging to control. Regarding biological control, the parasitoid Necremnus tutae Ribes & Bernardo (Hymenoptera: Eulophidae) is widely present around the Mediterranean basin and has adapted to the invader playing a substantial role in its control. In addition, the neotropical parasitoid Dolichogenidea gelechiidivoris Marsh (Hymenoptera: Braconidae) has established accidentally following its host in Spain and Algeria and a classical biological control program using this species is ongoing in Sub-Saharan Africa. Understanding the trophic connections between D. gelechiidivoris, N. tutae, the targeted host T. absoluta and potential non-target hosts is essential to assess their value as augmentative or classical biological control agents and to promote their establishment in conservation biocontrol. We conducted host-specificity tests in the laboratory using four European leafminer species to evaluate the specificity of these two parasitoids to T. absoluta. We then assessed their affinity for T. absoluta by exposing sentinel plants with the alternative host Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae) inside and around greenhouses and measuring each parasitoid species' field parasitism rate. Our results show that of the four non-target species tested in the laboratory, N. tutae attacked three, while D. gelechiidivoris attacked only P. operculella. In the greenhouse, N. tutae did not prefer P. operculella or T. absoluta, whereas D. gelechiidivoris preferred the latter. The mean parasitism rate of T. absoluta over the three-month monitoring period in the greenhouses reached 27 % for N. tutae and 35 % for D. gelechiidivoris. We discuss the importance of host affinity for understanding potential non-target effects and the value a natural enemy can have as biological control.