Ecological attributes of the single, successful Calosoma (Coleoptera: Carabidae) introduction to the Hawaiian Islands

From 1897 to 1957, numerous species of Calosoma carabid beetles were intentionally introduced to the Hawaiian Islands for biological control of invasive armyworm caterpillars (Lepidoptera: Noctuidae). In all, over 13 introductions, 8 Calosoma spp. were introduced; all without successful establishment. Yet another species, Calosoma anthracinum Chaudoir, now resides on Hawaii Island. We present how this species became established based on analysis of biological control explorations undertaken by Albert Koebele and H. T. Osborn in Mexico and the southwestern United States. The various purposeful introductions were hampered by several factors, including inadequate numbers of released individuals, the mixing of more than one Calosoma species in field releases, and the lack of lepidopteran prey outbreaks associated with the predator releases. Conversely, the sole successful, and accidental, introduction of C. anthracinum that occurred during these biological control efforts, resulted in a persistent population of this species in grassland habitats of Hawaii Island. The signal difference between the failed introductions and the successful colonist lies in the macropterous, flight-capable condition of the failures versus the brachypterous, flight-incapable condition of the successful colonist, C. anthracinum. We compare ecological and distributional attributes of boom and bust Calosoma predators that actively fly over long distances to aggregate at caterpillar outbreaks, versus the geographically restricted brachypterous species that represents the only successful colonist. The comparison suggests several interesting avenues for further research into this colonization success story.