Preference and performance of Polymorphomyia basilica on different phenotypes of Chromolaena odorata and other Asteraceae in the laboratory

Thandeka Mahlobo^1,2*Nontembeko Dube²Costas Zachariades³Caswell Munyai¹

• ¹University of KwaZulu-Natal, Durban, South Africa
• ²University of the Free State, Bloemfontein, South Africa
• ³Agricultural Research Council, Pretoria, South Africa

Chromolaena odorata, a weed of neotropical origin, is not yet under adequate biological control in South Africa. A stem-galling fly, Polymorphomyia basilica, was imported into the country and shown to be largely host-specific under no-choice conditions. This study used multi-choice and no-choice trials to test five non-target plant species previously selected by P. basilica in no-choice trials, and assessed the fly's preference and performance on various C. odorata phenotypes, including the southern African biotype (SAB) and the Asian/West African biotype (AWAB). Survival and development rates of P. basilica were highest on C. odorata (SAB) and Ageratum conyzoides. Only a few galls produced adult flies on S. africanus and C. macrocephalum, and emerging adults had low longevity. Polymorphomyia basilica showed a strong preference for and performance on C. odorata SAB in both settings, with over 90% of the progeny surviving to adulthood. Many larvae also developed successfully on the C. odorata Taiwan 129/130 phenotype, a representative of the AWAB biotype, and on the Jamaican 117 phenotype, whereas development was poorer on other phenotypes. Although the basis for this variation remains unclear, these trials indicate that P. basilica is suitable for release as a biocontrol agent against C. odorata in South Africa and capable of sustaining populations on the AWAB where it is invasive.