Waterlettuce Weevil Neohydronomus affinis Hustache, 1926 (Insecta: Coleoptera: Curculionidae)

Neohydronomus affinis Hustache is known as the waterlettuce weevil (Figure 1). It is a biological control agent of the floating plant, waterlettuce, Pistia stratiotes Linnaeus (Araceae) (O’Brien & Wibmer, 1989; Center et al., 2002). Waterlettuce is found in tropical and subtropical regions of the world. It infests slow-moving streams, waterways, lakes, and rivers, forming dense floating mats that are composed of several rosettes connected by stolons (runner stems). The presence of waterlettuce mats diminishes biological diversity and generates obstructions for boating, waterflow, and aquatic organisms (Cordo & Sosa, 2000; Dray & Center, 2002). Even though waterlettuce was documented by explorer William Bartram in Florida before 1765 (plants-archive.ifas.ufl/plant-directory), it is listed as a class II prohibited aquatic plant in the State of Florida. There are three species in the genus Neohydronmus, all of which originate from South and Central America. These weevils are subaquatic, and their exoskeletons are covered in white scales with no water-resistant features. The three species are all associated with waterlettuce and feed exclusively on it (Center et al., 2002; O’Brien & Wibmer, 1989). Among them, N. affinis was first introduced as a biological control agent into Florida in 1987 at Torry Island and Kreamer Island at the south end of Lake Okeechobee (Dray et al., 1990; 2001). Since then, the insect has successfully established itself in peninsular Florida and is also reported in Louisiana (Center et al., 2002).