Research on Harmonia axyridis in South Africa: knowns, unknowns and flags
Ingrid A. MINNAAR1, Cang Hui2,3, Susana Clusella-Trullas1
1Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University
2Centre for Invasion Biology, Department of Mathematical Sciences , Stellenbosch University, Matieland 7602, South Africa
3Mathematical and Physical Biosciences, African Institute for Mathematical Sciences, Cape Town 7945, South Africa
The harlequin ladybird Harmonia axyridis is a globally invasive beetle native to Asia. Its establishment and spread has led to the decline of native ladybird species in many regions of the world. In South Africa, it was first detected in the early 2000s in the Western Cape Province and has rapidly spread, currently found in all nine provinces. My PhD research has shown that H. axyridis has similar or a narrower temperature tolerance range than native ladybird species but has increased plasticity of upper temperature tolerance. Annual field collections of H. axyridis from 2013-2016 in Stellenbosch have highlighted how little we know about the species’ abundance and phenology, its interactions with native and other alien ladybirds and its impact on native species in South Africa. Current work includes the plasticity of life-history traits and starvation resistance of H. axyridis and its native counterpart Cheilomenes lunata in order to model these species’ potential distributions and population growth under future climate change scenarios. We have also uncovered new records of a parasitoid wasp and an ectoparasitic fungus that infest H. axyridis. These findings may contribute to devise methods to regulate invasive populations of H. axyridis. Finally, we have started a citizen science initiative with the aim to educate the public about this species, gather distribution records and collect specimens across the country. These data will be used to determine pathways of introduction, dispersal rates between geographic regions, and test hypotheses of invasion history using molecular techniques, thereby greatly informing management policies.