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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. [ABSTRACT FROM AUTHOR]

The tephritid Cecidochares connexa has been used to good effect as a biological control agent on the Asian/West African biotype of the invasive alien shrub Chromolaena odorata, but does not develop well on the different, southern African C. odorata biotype. A stem-galling tephritid fly, Polymorphomyia basilica, from the northern Caribbean islands, was considered as a potential biological control agent for C. odorata in South Africa. Life history traits and host range on 32 asteraceous plants were investigated in single-choice tests and using single pairs of adults in no-choice tests, under laboratory conditions. Positive biological characteristics of P. basilica include a high rate of increase, the production of several generations per year, long-lived and mobile adults, the ability of females to produce viable offspring without repeated mating, and the ability of adults to eclose from galls on dry stems. Use of a single pair of adults for no-choice tests proved to be efficient. Oviposition and larval development through to adulthood occurred on three other South American and on two South African species; for the latter, one was in the tribe Eupatorieae, closely related to C. odorata, and the other in the Astereae, less closely related to the weed, but both at a lower and slower rate. Females tended to retain their eggs under no-choice conditions in the presence of an unsuitable host, and to compensate by ovipositing at a higher rate when presented later with a C. odorata plant. The poor offspring survival on non-target plants tested in this study demonstrates the suitability of P. basilica for release in South Africa. [ABSTRACT FROM AUTHOR]