Development of eco-friendly methods for monitoring and regulating the box tree pyralid, Cydalima perspectalis (Lepidoptera: Crambidae), an invasive pest in ornamentals

As a monophagous herbivorous species that is native to Asia, the Box tree pyralid Cydalima perspectalis Walker (Lepidoptera: Crambidae) is one of the accidentally introduced non-native species that successfully survived, reproduced and became established in Europe. The aesthetic damage and total loss of Buxus is not only limited to local plantings, but also extends widespread in urban areas as well as to the natural Buxus stands, which are already affected or remain highly endangered. The objective of this investigation was the implementation of an effective, eco- and user friendly method for regulating C. perspectalis and preserving unaffected Buxus plants, based on usable biocontrol agents as well as on an effective monitoring system. The occurrence of wild populations of C. perspectalis and seasonal moth flight activity was recorded by pheromone and light traps between 2012 and 2015 in Hessia (GER). Both trap systems were found to be suitable for monitoring C. perspectalis that is required to allow the proper timing of control measures. Two main flight periods were identified, which indicate the existence of two generations. Basic data on the sex ratio (on average 43% ± 10% females) and the appearance of the melanic phenotype (on average 14% ± 2.9%) were collected. The ability of eight parasitoid Trichogramma species to parasitize and locate C. perspectalis eggs was assessed in the laboratory. Despite all tested species examined and oviposited into exposed eggs, resulting parasitation rates were low and ranged between 4% and 20% for most of the species. Only T. dendrolimi parasitized significantly more eggs with rates above 40%. Potentially egg defensive mechanisms were suggested that may impede higher parasitization. Thus, no specialized Trichogramma species had been found yet for a practicable inundative release. The beneficials Chrysoperla carnea Stephens (Neuroptera: Chryspidae) and Orius majusculus Reuter (Heteroptera: Anthocoridae) preyed on C. perspectalis eggs in experimental studies on prey acceptance and prey location on Buxus plants. C. carnea preyed on average 89% offered eggs during the prey acceptance bioassay and 49% offered eggs during the prey location on the Buxus plant within 72 h. In contrast, O. majusculus preyed only 41% and 13%, respectively. Therefore, the conservation of natural enemies as O. majusculus and the inundative release of beneficials such as C. carnea can be considered as supporting tools in the biological control of C. perspectalis. Susceptibility of C. perspectalis to the prospective biological control agents Neem (NeemAzal®-T/S) and Entomopathogenic nematodes (Nemastar®) was assessed in laboratory bioassays and field trials. When NeemAzal®-T/S treated leaf discs were consumed by larvae, a significant effect on vitality and feeding activity was noted after 14 days of exposure (47%-62% mortality; 10% of larvae were still feeding). Larvae (2nd and 4th developmental stage) demonstrated high susceptibility to Nemastar® (50 EPN per larva caused 100% mortality after 7 days). Both agents were much less reliable in their efficacy in field trials in comparison to the constant effectiveness of Bacillus thuringiensis. Their use is only possible in smaller areas, if individual feeding damage will be observed and proper surveillance will be considered. Potential repellent and toxic properties of 13 plant oils and extracts on egg deposition of C. perspectalis female moths and larval mortality were investigated in the greenhouse and the laboratory. When Thymus vulgaris L. and Malaleuca alternifolia M. & B. treated leaf discs were offered to larvae, a significant effect on feeding deterrence, survival and larval weight was noted. T. vulgaris was the most effective oil considering repellent and toxic effects. Its effective lethal concentration (LC50) was determined to be 1% (v/v) at 72 h. None of the tested control options alone provide an opportunity for the effective, eco- and user friendly regulation of C. perspectalis. The application of products based on B. thuringiensis is still the only highly effective and available biological control method but new approaches dealing with moth behaviour manipulation are promising, since the concept leads to the preservation of unaffected Buxus plants. In conclusion, the regulation of the invasive Box tree pyralid C. perspectalis still remains a major challenge for all concerned parties, even 10 years after its introduction.