Assessing the potential role of the native parasitoid Exorista larvarum (L.) as a biocontrol agent against Cydalima perspectalis (Walker): a laboratory evaluation

The Box Tree Moth (BTM), Cydalima perspectalis (Walker) (Lepidoptera: Crambidae), is an insect pest native to East Asia that has quickly spread across the Holarctic region through the trade of infested ornamental plants. Since its first record in Europe in 2006, it has posed a serious threat to Buxus species in both urban and natural environments. While several natural enemies control BTM populations in its native range, only a few native species have been recorded in field conditions in Europe, exhibiting low parasitism rates. Recently, the tachinid fly Exorista larvarum (L.) (Diptera: Tachinidae), a native larval endoparasitoid, has been observed parasitising BTM in field conditions in Europe. In this study, the potential of E. larvarum as a biocontrol agent against BTM was evaluated in laboratory conditions. A colony of E. larvarum, maintained on the greater wax moth Galleria mellonella (L.) (Lepidoptera: Pyralidae), was used to assess host acceptance and suitability through no-choice and choice tests. Acceptance rates were high for both hosts (no-choice: 97% for BTM, 88% for G. mellonella; choice: 60% for BTM, 100% for G. mellonella). Larval mortality was also high (no-choice: 71% for BTM, 89% for G. mellonella; choice: 71% for BTM, 97% for G. mellonella). Conversely, host suitability varied significantly between the exotic and factitious hosts: puparia formation and adult emergence were higher in G. mellonella, unlike BTM (no-choice: 83% vs. 3%; choice: 87% vs. 11%). Although E. larvarum showed a preference for G. mellonella, our findings suggest that this parasitoid species can complete its life cycle on BTM, albeit at very low rates, contrary to previous studies. These results may suggest emerging changes in the behavioural dynamics of this host–parasitoid relationship, highlighting the need for further research to clarify the potential role of E. larvarum as a BTM biocontrol agent.