Reservoir host plants can play a critical role in the maintenance and spread of invasive agricultural insect pests, particularly when the pest species attacks a wide range of host plants, is ecologically plastic and demonstrates high reproductive fitness. The tomato leafminer, Tuta absoluta Meyrick (Lepidoptera: Gelechiidae), fits well within this category of alien pests. Indeed, this moth has become, in a very short period, the main phytosanitary factor limiting tomato production in the world. In addition, it is becoming a potential pest of potato crops. Among reported host weeds of this insect, Solanum nigrum L., Datura stramonium L. and Datura ferox L. are widely distributed in both T. absoluta's original geographical range and in newly infested areas. In this paper, we assess the suitability of these three plants as alternate hosts for T. absoluta. Development time of juvenile instars, adult longevity and female fecundity of the pest reared on these weeds were compared with those observed on tomato and potato plants under laboratory conditions. The study revealed that T. absoluta did not oviposit and develop on either D. stramonium or D. ferox. Conversely, tomato leafminers reared on S. nigrum (black nightshade) exhibited a reproductive fitness comparable with that seen on potato. All the investigated parameters confirmed that tomato is the most suitable host plant for the pest. These findings highlight the potential of the black nightshade to act as a reservoir host for T. absoluta and the carryover of its populations in periods when neither tomato nor potato crops are available.