Systena nitentula (Coleoptera: Chrysomelidae), a flea beetle injurious to Alternanthera philoxeroides (Amaranthaceae): Redescription, biology, and distribution

Abstract

Flea beetles of alligator weed, <i>Alternanthera philoxeroides</i> (Martius) Grisebach (Amaranthaceae), were collected in Argentina, Uruguay, Paraguay, and Brazil. Species in the genera <i>Disonycha</i> Chevrolat, <i>Agasicles</i> Jacoby, and <i>Systena</i> Chevrolat were frequently found on this weed. <i>Systena nitentula</i> Bechyné 1954 was the most abundant within <i>Systena</i>. This species is reported for the first time from Argentina at north of 30° S. The male is described and holotype female is redescribed adding new diagnostic characters: mouthparts, hind wings, metendosternite, and male and female genitalia. <i>S. nitentula</i> is recognized by the combined characters of piceous elytra with J-shaped vittae, a small spermatheca pump, and internal median lobe sac with five sclerotized plates. Differences in color patterns between <i>S. nitentula</i>, <i>S. tenuis</i> Bechyné, and S. <i>s-littera</i> L. also are considered. <i>S. nitentula</i> presents three instars that can be separated through head width. New biological data based on laboratory rearing and field observations shows that <i>S. nitentula</i> could be a monophagous species strongly associated to the alligator weed growing in terrestrial conditions. This information promotes <i>S. nitentula</i> as a potential biocontrol agent of this invasive weed.