Native range assessment of classical biological control agents: impact of inundative releases as pre-introduction evaluation

Diadromus pulchellus Wesmael (Hymenoptera: Ichneumonidae) is a pupal parasitoid under consideration for introduction into Canada for the control of the invasive leek moth, Acrolepiopsis assectella (Zeller) (Lepidoptera: Acrolepiidae). Since study of the parasitoid outside of quarantine was not permitted in Canada at the time of this project, we assessed its efficacy via field trials in its native range in central Europe. This was done by simulating introductory releases that would eventually take place in Canada when a permit for release is obtained. In 2007 and 2008, experimental leek plots were artificially infested with pest larvae to mimic the higher pest densities common in Canada. Based on a preliminary experiment showing that leek moth pupae were suitable for parasitism up to 5–6 days after pupation, D. pulchellus adults were mass-released into the field plots when the first host cocoons were observed. The laboratory-reared agents reproduced successfully in all trials and radically reduced leek moth survival. Taking into account background parasitism caused by naturally occurring D. pulchellus, the released agents parasitized at least 15.8%, 43.9%, 48.1% and 58.8% of the available hosts in the four release trials. When this significant contribution to leek moth mortality is added to previously published life tables, in which pupal parasitism was absent, the total pupal mortality increases from 60.1% to 76.7%. This study demonstrates how field trials involving environmental manipulation in an agent's native range can yield predictions of the agent's field efficacy once introduced into a novel area.

Comparative life tables of leek moth, Acrolepiopsis assectella (Zeller) (Lepidoptera: Acrolepiidae), in its native range

Leek moth, Acrolepiopsis assectella (Zeller) (Lepidoptera: Acrolepiidae), is an invasive alien species in eastern Canada, the larvae of which mine the green tissues of Allium spp. This study was designed to construct and analyse life tables for leek moth within its native range. Stage-specific mortality rates were estimated for the third leek moth generation at three sites in Switzerland from 2004 to 2006 to identify some of the principle factors that inhibit leek moth population growth in areas of low pest density. The contribution of natural enemies to leek moth mortality was measured by comparing mortality on caged and uncaged leeks. Total pre-imaginal mortality on uncaged plants was 99.6%, 99.1% and 96.4% in 2004, 2005 and 2006, respectively. Variation in mortality was greater among years than among sites. Total larval mortality was greater than that in the eggs and pupae. This was due largely to the high mortality (up to 83.3%) of neonates during the brief period between egg hatch and establishment of the feeding mine. Leek moth pupal mortality was significantly greater on uncaged than on caged leeks, indicating an impact by natural enemies, and this pattern was consistent over all three years of study. In contrast, the other life stages did not show consistently higher mortality rates on uncaged plants. This observation suggests that the pupal stage may be particularly vulnerable to natural enemies and, therefore, may be the best target for classical biological control in Canada.

Taxonomic review of the leek moth genus Acrolepiopsis (Lepidoptera: Acrolepiidae) in North America

The North American species of Acrolepiopsis are reviewed and include six described species: A. assectella (Zeller), A. californica Gaedike, A. heppneri Gaedike, A. incertella (Chambers), A. leucoscia (Meyrick), and A. reticulosa (Braun). Acrolepiopsis liliivora Gaedike is considered a junior synonym of A. californica (new synonymy). Acrolepiopsis assectella, commonly known as the leek moth, is a recently invasive alien species in North America and a pest of the plant genus Allium, including leek, onion, garlic, and related cultivated plants. A key to species based on adults is provided, diagnostic characters including male and female genitalia are illustrated, and geographical distribution, host plants, and larval feeding pattern and damage (where known) are given. Diagnostics and illustrations are presented also for A. sapporensis (Matsumura); known as the Asiatic onion leafminer, it is very similar to A. assectella and is an invasive alien species present in Hawaii, though not in North America. Adult diagnostic characters of the genus Acrolepiopsis, the family Acrolepiidae, and the superfamily Yponomeutoidea are also provided and illustrated. DNA barcoding data (short sequences of the mitochondrial cytochrome c oxidase I gene) obtained for five of the six species revealed interspecific differences averaging 8.1%, whereas intraspecific variation was ≤ 0.16%, and provided unequivocal species separation matching morphology-based identifications.