Is oviposition and larval damage by the leaf-mining fly Calycomyza eupatorivora (Agromyzidae) on its target weed, Chromolaena odorata (Asteraceae), restricted by leaf-quality preferences?

Abstract

The leaf-mining fly Calycomyza eupatorivora Spencer (Diptera: Agromyzidae) was released in the eastern coastal regions of South Africa for the biological control of the invasive shrub Chromolaena odorata (L.) King and Robinson. Despite widespread establishment, its ability to inflict sufficient foliar damage has been questioned. This laboratory study was initiated to provide some insight into how increasing fly populations (represented by 1, 5 and 10 mating pairs per plant) are likely to influence leaf-mining intensity and the levels of damage. On average, individual plants exposed to five mating pairs displayed significantly more larval mines (248) than those exposed to single pairs (69), while plants exposed to 10 mating pairs were intermediate (125). Similarly, at densities of five mating pairs per plant, the percentages of available leaves that were exploited peaked at 36%, while the percentages of available leaf area that were removed by larval leaf mining peaked at 22%. The non-linear relationship between leaf mining and fly density and the high percentages of unexploited leaves suggest that leaf mining may be influenced by leaf quality, the nature of which is currently unconfirmed. These results also suggest that the levels of leaf exploitation by C. eupatorivora will be too low to have any meaningful impact in the field. Field evaluations, to be reported in a later contribution, have indeed confirmed that the impact of C. eupatorivora on mature populations of C. odorata is negligible.

Keywords:

• agent impact
• oviposition preferences
• triffid weed
• weed biological control

Acknowledgements

The ARC-Plant Protection Research Institute (Cedara) provided the laboratory facilities and equipment. Anonymous referees are thanked for their comments on the draft manuscript.

Funding

The Botanical Education Trust, Tata Africa Scholarship fund and Working for Water Programme (Department of Environment Affairs, South Africa) provided funding for the first author, who undertook this study as part of an M.Sc. dissertation.

Additional information

Funding

Funding: The Botanical Education Trust, Tata Africa Scholarship fund and Working for Water Programme (Department of Environment Affairs, South Africa) provided funding for the first author, who undertook this study as part of an M.Sc. dissertation.