South America
Waterlettuce (Pistia stratiotes)
Eggs are small, oval, and cream-colored. Larvae are up to 3 mm long and have a white or yellow body with a brown head capsule. Pupae are cream-colored and only up to 2 mm long. Adults are approximately 2 mm long and have a nearly straight snout with an obvious constriction at the base. Adults range from golden-brown to bluish-gray. Bare patches form on the elytra where the scales are rubbed off, giving the adults a chevron-like pattern. Females are usually slightly larger than males.
At warm locations, both Neohydronomus affinis and waterlettuce develop throughout the year; adults and pupae are the stages most often observed over winter. Adult females lay eggs singly in holes they chew in the upper surface of waterlettuce leaves near leaf margins. Larvae mine into leaves and feed towards the spongy tissue of leaves through three instars. This leaves a distinctive mining trail clearly visible in thin leaf tissue. Pupation occurs within leaves. Emerging adults feed on waterlettuce leaves, creating round feeding holes and occasionally chewing into the leaf spongy tissue. There are three generations per year in the native range.
Larval and adult feeding destroy leaf buoyancy, and attacked plants sink and die under high weevil densities.
Dray, F.A. and P.T. Madeira. 2022. Waterlettuce Biocontrol Agents: History and Ecology in North America. In: R.L. Winston, Ed. Biological Control of Weeds in North America. North American Invasive Species Management Association, Milwaukee, WI. NAISMA-BCW-2022-23-WATERLETTUCE-A. https://bugwoodcloud.org/resource/files/23230.pdf