South America
Alligatorweed (Alternanthera philoxeroides)
Eggs are white and oval-shaped. Larvae are white to yellow initially, appearing brown at maturity because of several tan, longitudinal, wavy stripes. Final instars are up to 14 mm long. Pupae are found in silken cocoons and turn from yellow to dark brown with age. Adult moths hold their wings tightly against their bodies; they are 13–14 mm long with a wingspan of 20 mm. Forewings are tan to brown with mottled markings. Adults have large “snouts” covered in scales as well as large dark eyes.
Adults emerge in spring, and females lay eggs singly at leaf axils or on the undersides of alligatorweed leaves. A single female may lay an average of 260 eggs in her lifetime. Larvae bore into stem tips and mine downwards, feeding on stem tissue through five instars. At maturity, larvae plug stem nodes beneath them with chewed tissue in order to seal out water and prepare adult exit “windows” by chewing stem tissue but leaving the epidermis intact. Larvae spin cocoons in which to pupate, and adults emerge through exit windows. In North America, the number of generations per year is unknown; 3–4 generations per year have been observed in the native range. Last generation larvae overwinter in alligatorweed stems and pupate the following spring.
Larval mining causes stems to wilt and eventually die, turning yellow as they do so. Entire mats often turn yellow and sink.
Harms, N.E., I.A. Knight, and P.D. Pratt. 2022. Alligatorweed 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-2022-25-ALLIGATORWEED-A. https://bugwoodcloud.org/resource/files/23221.pdf