Ecology, host specificity and impact of Atomacera petroa Smith (Hymenoptera: Argidae) on Miconia calvescens DC (Melastomataceae)

Miconia calvescens DC (Melastomataceae) is an invasive tree considered to be the greatest threat to natural ecosystems of Hawaii and other Pacific islands. The potential of the sawfly Atomacera petroa Smith (Hymenoptera: Argidae) as a biological control agent of M. calvescens was evaluated in field and laboratory studies in its native range in Brazil. At two field sites, 31.1% and 15.3% of the M. calvescens leaves sampled presented rasping damage by A. petroa larvae, affecting 2.0–66.7% (16.8% on average) of the area of each attacked leaf. Damage by A. petroa was significantly more frequent among older leaves (81.2% affected) than younger leaves (18.8% affected), and percentage of leaves damaged declined significantly with increasing stem diameter. Damage by individual A. petroa larvae feeding as first through sixth instars ranged from 304 to 924 mm2 (663 mm2 on average) of M. calvescens leaf material in the field. In the laboratory, A. petroa developed through the final three larval instars in 2.1, 2.5 and 3.1 d on average, respectively, pupated for 5–10 d, and survived as adults for 5–8 d. No feeding damage by A. petroa was observed on plant species associated with M. calvescens at field sites, including three other species of Melastomataceae, or on test plants exposed to A. petroa larvae in the laboratory, indicating that A. petroa has a narrow host range. Host specificity, foliar impact, and the likely absence of specialized natural enemies in Hawaii appear to justify further study of A. petroa as a biological control agent of M. calvescens.