Hesperomyces harmoniae: affect of abiotic factors and transmission to native ladybirds

The harlequin ladybird Harmonia axyridis (Coccinellidae, Coleoptera) was originally introduced as pest control in North America and Europe, where it became an invasive species (Roy et al. 2016). This resulted in a decline of locally native insects, including native ladybirds through both competition and predation (Roy et al. 2016). Hesperomyces harmoniae (Laboulbeniales, Ascomycota) is an ectoparasitic microfungus of Ha. axyridis (Haelewaters et al. 2022b). Previous work has shwon that He. harmoniae causes increased mortality of Ha. axyridis ladybirds in laboratory conditions (Haelewaters et al. 2020). This project will test the applicability of He. harmoniae as a potential biological control agent against Ha. axyridis by investigating whether it can also be transmitted to other coccinelids.

This research will consist of two parts. In the first part, Ha. axyridis ladybirds from multiple localities in Europe and North America will be screened for the presence of He. harmoniae. Parasite prevalence rates will be analyzed in light of biotic and abiotic factors. It is expected that development and prevalence rates will differ depending on both temperature and humidity (Haelewaters et al. 2022a, Santamaria 2023). The second part of the project will investigate the transmission of He. harmoniae to atypical hosts, i.e., non-Ha. axyridis ladybirds. If He. harmoniae were to be applied as a biocontrol agent against Ha. axyridis, it would have to be unable to infect native species of ladybird such as Adalia bipunctata, Coccinella septempunctata, and Propylea quatuordecimpunctata. Laboratory experiments will be performed during which infected Ha. axyridis will be placed together with uninfected Ha. axyridis, A. bipunctata, C. septempunctata, and P. quatuordecimpunctata, respectively. It is expected that intra-specific transmission (to Ha. axyridis) will be high but inter-specific transmission will be low (Cottrell & Riddick 2012).


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