Distribution and abundance of a threatened stem-boring moth, Houdinia flexilissima, (Lepidoptera: Batrachedridae) in New Zealand peat bogs

Abstract

The threatened stem-boring moth, Houdinia flexilissima (Lepidoptera: Batrachedridae), is known only from one host plant, Sporadanthus ferrugineus, which is also threatened. Sporadanthus ferrugineus is known from three isolated peat bogs in the Waikato region, New Zealand (Kopuatai, Torehape and Moanatuatua) and four other wetlands following translocation (Lake Komakorau, Lake Serpentine and Waiwhakareke) or restoration (Torehape peat mine). The distribution and abundance of H. flexilissima was assessed using a new monitoring technique which involved counting, harvesting and dissecting the Sporadanthus stems for the presence of larvae. The moth was found in natural, translocated and restored wetlands. Houdinia flexilissima appears to be able to survive wherever S. ferrugineus plants are present, and is most common in stems 2.0-4.5 mm in diameter. It has established in small translocated populations (≤270 m2) from larvae contained within stems of the original translocated Sporadanthus plants, and at the restoration site by dispersal from adjacent natural populations 800 metres away. From a conservation perspective, the pattern of population establishment in the absence of additional interventions is encouraging for the long-term persistence of H. flexilissima. Herbivory rate, larval density and larval size varied with the time since translocation, age of the restoration plantings and size of the natural wetlands. The sampling method used could be applied to ecological studies investigating other stem-boring Lepidoptera taxa.