Insect Herbivores Associated with Nymphaea mexicana (Nymphaeaceae) in Southern United States: Potential Biological Control Agents for South Africa

Nymphaea mexicana Zuccarini (Nymphaeaceae) (Mexican waterlily) is an emergent floating-leaved aquatic plant from the southeastern USA that is invasive in South Africa. In invaded waterbodies this plant restricts water movement, increases siltation, decreases recreational activities, and can deplete water oxygen levels, which in turn negatively impacts aquatic fauna. Currently there are no chemical, mechanical, or biological control programs in place for N. mexicana in South Africa, but the sustainability of biological control makes this the most desirable option. Field surveys for potential biological control agents were conducted in the native range of N. mexicana in Florida, Louisiana, and Texas from Aug to Oct 2018. Leaves, stems, flowers, and roots of N. mexicana were searched for insect herbivores by hand and using Berlese funnels. Insects were prioritized for use as biological control agents by considering the extent and type of feeding damage, field host range, and incidence (percentage of sites in which each species was found). In total, 15 confirmed species were found feeding on N. mexicana, and some taxa were identified only to family level. Incidence coverage estimator mean, MMRuns, Chao 2 mean, and Chao 2 upper 95% CI species accumulation estimators predicted that between 2 and 5 species were missed during the surveys. Based on field observations, Bagous americanus LeConte (Coleoptera: Curculionidae), and Megamelus toddi Beamer (Hemiptera: Delphacidae) were prioritized. Host specificity trials will be conducted to determine whether these insects may be used as biological control agents of N. mexicana.