Compatibility of the invasive alien lemna minuta and its potential biocontrol agent cataclysta lemnata

The American duckweed Lemna minuta is invasive in freshwater habitats across much of Europe, often causing serious ecological impacts. To date, few studies have addressed how to halt its expansion. However, encouraging empirical evidence of L. minuta control by the aquatic herbivorous larvae of the insect Cataclysta lemnata is emerging. To better understand the biocontrol capacity of C. lemnata, information on overlap in the phenology and the growth conditions in nature of both species is fundamental. In this study, L. minuta and C. lemnata populations were analyzed in the field to define (i) their phenological features, (ii) the main environmental characteristics where the two species occur, and (iii) any overlap or difference in phenology and ecological requirements. The seasonal occurrence of the two species and environmental data were collected from 31 wetlands in central Italy. The two species showed a large phenological overlap and ecological similarities. Populations of L. minuta and C. lemnata were found all year long, although abundances were greater in spring and summer. Both species preferred waters that were shallow, circumneutral, with moderately high conductivity and trophic level and with low dissolved oxygen. The phenology and ecology of the two species were shown to be compatible, suggesting the insect could be released in natural sites invaded by the alien L. minuta where could act as potential biocontrol agent of it.