South America
common salvinia (Salvinia minima), giant salvinia (S. molesta)
Eggs are white, elliptical, and small (½ mm long). Larvae are less than 2 mm long, white, C-shaped, and have brown head capsules. Adults are up to 2 mm long and have a long snout. Females are usually larger than males. Newly emerged adults are brown, but within a few days, their color changes to a shiny black. They have ridges and pits along their body with tiny golden scales.
Females can produce about 300 eggs in their lifetime and lay them in young plant tissue. Larvae feed externally on buds before burrowing to feed within rhizomes. There are three larval instars. Pupation occurs underwater in cocoons attached to the rhizome. Emerging adults feed on buds and fronds, leaving a distinctive “shot-hole” feeding pattern. Adults may live 20–38 weeks in optimal conditions. Adults are typically found at the base of the buds or within the submerged filaments. When adults are underwater, a film of air trapped beneath their body allows them to breathe. In North America, the number of generations varies by climate; there is likely one generation per year at colder locations and three at warm sites such as in southern Louisiana and Texas.
While adult feeding helps suppress plant growth, larval feeding causes the most damage. When the larvae damage the rhizomes, it halts nutrient uptake. Feeding damage is identified by the scarring and “shot-hole” feeding pattern on the buds along with discoloration of the fronds. Over time, the plants will turn from a healthy green to yellow to brown, disintegrate, and eventually sink. Under optimal conditions, this damage is sufficient to manage salvinia; at many other sites, it is necessary to integrate biological control with other management efforts.
Pham, K., R. Diaz, and J.G. Nachtrieb. 2022. Salvinia 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-2022-20-SALVINIAS-A. https://bugwoodcloud.org/resource/files/26407.pdf