Effect of interspecific competition in regulating populations of C. capitata and C. rosa in various fruit kinds

The objectives of the project were to (1) determine the suitability of commercial fruits for the development of two fruit fly pest species: Ceratitis capitata (Medfly) and C. rosa (Natal fly) and (2) investigate interspecific interactions of adults on host fruit and larval competition between species at constant temperature in the laboratory.  Oviposition responses, adult and larval interspecific interactions were investigated on different fruit kinds (orange, lemon, peach, pear, plum, grape, apple and grapefruit). Laboratory colonies, initiated from field collected flies, were used.

Both fruit fly species were able to develop in all commercial fruit tested except grapefruit. Although females of both species accepted grapefruit for oviposition, no pupae were recovered and this fruit was therefore omitted from further experiments.  Significant interactions were observed amongst adults of the two species on the various fruit tested whereby Medfly dominated in most fruit. There were also some indications of interspecific competition at larval stages for some fruit kinds- apple, lemon and grape- whereby when these fruits were offered first to either Medfly or Natal fly and thereafter exposed to the other species, more Medfly adults were reared compared to Natal fly adults, although differences were not significant.  Orange, peach and plum were most favourable for oviposition for both species, whilst lemon was the least favourable.  Peach, plum and pear obtained significantly higher emergence rates for both species, than the other fruit.  Medfly adults showed longest survivorship and highest fecundity.

Results from the laboratory tests indicate that the two fly species are likely to occupy similar host niches and are able to compete on and possibly within some hosts with the outcome of competition varying according to host types. In the field however, other factors such as temperature and humidity are likely to further influence the degree and outcome of such competitions.