Seasonal activity, habitat preferences and larval mortality of the leaf-mining flyCalycomyza eupatorivora(Agromyzidae), a biological control agent established onChromolaena odorata(Asteraceae) in South Africa

Abstract

The leaf-mining fly Calycomyza eupatorivora Spencer (Diptera: Agromyzidae) has become widely established in the eastern regions of South Africa, following its release for the biological control of the invasive shrub Chromolaena odorata (L.) King and Robinson. This study was conducted to gain some insight into the impact of C. eupatorivora populations, by assessing their seasonal activity, habitat preferences, levels of leaf exploitation and extent of larval mortality in the field over a 1-year period. Leaf mining intensity was poorly synchronised with leaf availability, with leaf exploitation peaking at the end of the growing season of C. odorata. Although significantly more mines were recovered on plants growing in shaded situations, the percentage of available leaves that were exploited for mining was not significantly different between plants growing in shaded versus open situations. Overall, the levels of leaf damage were trivial with mines recovered from <5% of available leaves that were sampled during the study. Besides leaf-quality requirements, these low levels of leaf exploitation may have been influenced by high larval mortality which varied between 60 and 83%, depending on whether lower or higher estimates were used. These evaluations have verified the results of earlier laboratory studies which suggested that the impact of C. eupatorivora on mature populations of C. odorata in South Africa will be negligible.

The nocturnal larvae of a specialist folivore perform better on Chromolaena odorata leaves from a shaded environment

“…However, plants growing in full‐sun were firm and more upright and had increased biomass of leaves and stems compared with shaded plants. This increase in biomass of plants growing under full‐sun conditions has been previously documented in herbaceous plants (Moran & Showler, ) and shrubs (Valladares & Pearcy, ; Diaz et al., ) such as C. odorata (Nzama et al., ). Our findings not only concur with that of Zachariades et al.…”