The leafminer Coptodisca sp. (Lepidoptera: Heliozelidae), recently recorded for the first time in Europe on Italian black and common walnut trees, is shown to be the North-American Coptodisca lucifluella (Clemens) based on morphological (forewing pattern) and molecular (cytochrome oxidase c subunit I sequence) evidence. The phylogenetic relatedness of three species feeding on Juglandaceae suggests that C. lucifluella has likely shifted, within the same host plant family, from its original North-American hosts Carya spp. to Juglans spp. Over the few years since its detection, it has established in many regions in Italy and has become a widespread and dominant invasive species. The leafminer completes three to four generations per year, with the first adults emerging in April–May and mature larvae of the last generation starting hibernation in September–October. Although a high larval mortality was recorded in field observations (up to 74%), the impact of the pest was substantial with all leaves infested at the end of the last generation in all 3 years tested. The distribution of the leafminer in the canopy was homogeneous. The species is redescribed and illustrated, a lectotype is designated and a new synonymy is established.

The effects of Bt transgenic cottons (Bt-I expressing cry1Ac and Bt-II expressing cry1Ab and cry2Ab or cry1Ab and cry1Fa) and non-Bt cottons on feeding, oviposition and longevity of adults, and development and survival of Liriomyza trifolii larvae were studied under laboratory conditions; and infestation on four Bt and two non-Bt cotton traits were investigated under field conditions. Laboratory choice and no-choice tests showed that L. trifolii adults were capable of distinguishing between Bt cottons and non-Bt cottons. In a choice test on younger plants (4–5 leaves), the adults were found more often and made more feeding punctures (FP) on non-Bt cottons than on Bt cottons. On older plants (8–9 leaves), adults made the most FP on non-Bt cotton followed by those on Bt-II cottons and the least on Bt-I cotton. The females oviposited more eggs (6.7 eggs per leaf) on non-Bt cotton than on Bt-I (1.7 eggs per leaf) and Bt-II (0.8 eggs per leaf) cottons on younger plants and oviposited similar numbers of eggs (0.7–1.3 eggs per leaf) on non-Bt and Bt cottons on older plants. In a no-choice test, the females also fed more FP on non-Bt cottons than on Bt cottons on both younger and older plants. The females oviposited more eggs (15.6 eggs per leaf) on non-Bt cotton than on Bt-I (8.2 eggs per leaf) and Bt-II (6.5 eggs per leaf) cottons on younger plants and similar numbers of eggs (2.5–3.3 eggs per leaf) on non-Bt and Bt cottons on older plants. Larval and puparial survivals were not different among Bt and non-Bt cottons. The occurrence and damage of leafminers on cottons in the field showed that L. trifolii infested more plants and leaves and had more mines on non-Bt cotton than on Bt cottons.

The leafminer, Liriomyza trifolii Burgess, a polyphagous agricultural pest, can attack crops at different stages of development; some are attacked at the beginning of the crop cycle and others at the end of the cycle. Experiments on the differential susceptibility of the bean Phaseolus vulgaris and the potato Solanum tuberosum plants were done to get some information about factors which influence host selection by the leafminer. The distribution and density of leaf trichomes, as well as the nutritional status of the host plants, were found to be important in host selection. High trichome density acts as a physical deterrent to Liriomyza flies, just as senescing primary bean leaves induce non-acceptability. When given a choice, flies prefer bean to potato leaf discs, though the latter possess less trichomes. Other factors (chemical attractants and some nutrient components) might therefore also be involved in the complex host selection behaviour of L. trifolii.