Interspecific competition between Drosophila suzukii and Zaprionus indianus larvae in rearing medium and grapes

Drosophila suzukii (SWD) and Zaprionus indianus (AFF) are two recently introduced invasive species to the US.  Both are important pests in vineyard systems; SWD causing direct damage to the grape clusters through oviposition and both species infecting grape clusters with pathogens.  An interspecific density effect study was conducted for SWD and AFF using commercial media and wine grapes. SWD and AFF eggs were placed onto a 0.38 g block of molasses media or a single Petit Verdot grape in a range of densities.  The densities tested were 1:1, 2:2, and 4:4 for media and 4:4 and 8:8 on grapes.  Controls for each species were also tested with 2, 4 and 8 fly eggs on media and 8 and 16 on grapes, so any interspecific competition could be detected.  Larval competition or interactions were evaluated based on developmental time, pupal volume and lifetime egg production for female flies that emerged.