Impact of the gall-inducing fly Polymorphomyia basilica Snow (Diptera: Tephritidae) on the growth and reproduction of Chromolaena odorata (L.) R.M.King & H.Rob (Asteraceae) in the laboratory

Abstract

Gall-inducing insects are a classic example of how insects can impact the morphology and physiology of their host plants by forming galls which act as nutrient sinks. An 8-months laboratory study was conducted to determine the impact of the galls induced by Polymorphomyia basilica oviposition and or the subsequent larval feedingon the growth and reproduction of Chromolaena odorata. Three treatment levels were used, viz. control: 0% of the shoots were exposed, low infestation: 50% of shoots were exposed, and high infestation, where 100% of the shoots were exposed for P. basilica to oviposit for 48 h each month. Results showed that P. basilica oviposition and or the subsequent feeding by larvae reduced the height and flower production of C. odorata plants but promoted lateral growth by increasing the number of shoot tips. Basal stem diameter was not affected by the presence of the galls. The presence of galls also decreased the leaf and root dry biomass on the treated plants but had no significant impact on stem biomass. The difference between the low- and high-infestation treatments was only significant for root biomass, suggesting that more galls are required for the roots to be affected. Overall, the study showed that P. basilica meets the requirements of an effective biocontrol agent against C. odorata in South Africa. Its release should complement the already released agents in reducing the fitness and productivity of C. odorata.