Interactions between the fungal pathogen Beauveria bassiana and three species of coccinellid: Harmonia axyridis, Coccinella septempunctata and Adalia
bipunctata |
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Authors: | Helen Elizabeth Roy Peter M J Brown Peter Rothery Remy L Ware Michael E N Majerus |
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Institution: | (1) NERC Centre for Ecology and Hydrology Monks Wood, Huntingdon, PE28 2LS, UK;(2) Department of Life Sciences, Anglia Ruskin University, East Road, Cambridge, CB1 1PT, UK;(3) Department of Genetics, University of Cambridge, Downing Street, Cambridge, CB2 3EH, UK |
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Abstract: | Harmonia axyridis is a predatory coccinellid, native to central and eastern Asia. It has been available in many countries for use as a biological
control agent of pest aphids and scale insects. In many of these countries, including the USA, H. axyridis has established. It is now considered an invasive alien species for a number of reasons, including its impact on functional
biodiversity. Beauveria bassiana is known to be a natural mortality agent of overwintering coccinellids and is a potential candidate for the biological control
of H. axyridis. In this paper we compare the susceptibility of three species of coccinellid, H. axyridis (cultures derived from Japan and UK), Coccinella septempunctata and Adalia bipunctata to infection by B. bassiana (commercial strain GHA) after exposure at three doses (105, 107, 109 conidia ml−1). The two subpopulations of H. axyridis (Japan and UK) were more resistant to B. bassiana infection than either A. bipunctata or C. septempunctata. This is exemplified by the median lethal doses at 10 days post-inoculation (LD50) of 106.2, 106.0, 108.3, 109.6 conidia ml−1 for A. bipunctata, C. septempunctata, H. axyridis (Japan) and H. axyridis (UK), respectively. Only doses of 109 conidia ml−1 resulted in mortality of H. axyridis, in contrast, 80% of C. septempunctata and 70% of A. bipunctata exposed to 107 conidia ml−1 of B. bassiana succumbed to infection. The fecundity (cumulative mean egg production over 10 days) of A. bipunctata and H. axyridis (UK) was also assessed. The fecundity of C. septempunctata could not be assessed because this species requires diapause prior to the onset of reproduction and these studies were on
beetles that had recently eclosed (2–8 weeks). Harmonia axyridis (Japan) produced no eggs in most treatments including the control and so was excluded from analysis. High dose (109 conidia ml−1) inoculation reduced the fecundity of A. bipunctata to zero but egg production was similar for individuals inoculated with doses of 105, 107 conidia ml−1 and control individuals. In contrast, all doses of B. basssiana reduced H. axyridis (UK) egg production dramatically. We discuss these results in relation to the potential for control of H. axyridis using B. bassiana. |
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Keywords: | Beauveria bassiana Harmonia axyridis Coccinella septempunctata Adalia bipunctata Fungal entomopathogen Coccinellidae Invasive alien species Native species Biological control |
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