A new species, Haplothrips heliotropica, is described from Argentina causing severe damage to the leaves of Heliotropium amplexicaule (Boraginaceae), a South American plant that is now a serious weed of pastures in Australia. Observations are presented on the host specificity, seasonal population changes and overwintering of this thrips. The genus Haplothrips includes more than 230 species worldwide, mostly feeding in flowers. In contrast, adults and larvae of H. heliotropica feed exclusively on green tissues. This is only the third South American species of Haplothrips. Character states are given for distinguishing these three species, and also for Haplothrips heliotropii Priesner from Egypt and Yemen.