Native Lygus spp. (Heteroptera: Miridae) damaging introduced Hibiscus cannabinus in Italy

Kenaf, Hibiscus cannabinus L, an introduced tropical fiber crop, is attacked in central Italy by the native mirid bugs Lygus rugulipennis Poppius and L. pratensis (L.), thus establishing novel insect-plant associations. Feeding by Lygus bugs damages the apical meristem, with consequent development of secondary stems and leaf tattering. In a laboratory experiment, both species caused apical meristem damage on potted kenaf. In a field experiment with caged plots, the percentage of damaged plants was significantly higher in plots artificially infested with multiple releases of Lygus spp. compared with a single release and with the protected control without Lygus spp. In naturally infested control plots, the percentage of damaged plants was intermediate. Plant height decreased as a function of the number of damaged meristems. Mean plant height was significantly lower in the multiple-release treatment compared with the single-release treatment and the protected control. Dry biomass was significantly lower in the multiple-release plots compared with the protected control, and intermediate in the single-release plots. In a field experiment with three kenaf cultivars naturally infested by Lygus spp., plant height and stem diameter were significantly lower in damaged plants compared with healthy plants. Dry weights of plants, stems, and basts were also lower, depending on the cultivar, whereas the bast/core ratio was not affected. Stem lesions developed due to feeding or incisions made by ovipositing females. Lesions and eggs were significantly more abundant on plants with damaged apical meristems compared with healthy plants. Damage mechanisms by Lygus spp. and consequences of new crop introductions are discussed.