In studies of frugivorous tephritids, determining when offspring (i.e. egg and three larval instars) mortality occurs within the fruit can greatly improve the mechanistic understanding of the fly/host interaction.  Previous research has demonstrated that the Queensland fruit fly, Bactrocera tryoni, has differential offspring performance in two tomato cultivars Cherry and Roma, but when juvenile mortality was occurring was not determined.  We examined B. tryoni egg and larval survival in three different ripening stages (immature-green (IG), colour-break (CB) and fully-ripe (FR)) of Cherry and Roma tomato cultivars through destructive fruit sampling at 72 and 120 hrs for eggs, and 48 (1^st instar), 96 (2^nd instar) and 120 hours (3^rd instar) after fruit inoculation with neonates for larvae. Cultivar and ripening stage had no significant effect on egg survival, nor larval survival at 48 hrs: egg survival was high across all treatments, while 1^st instar larval was low across all treatments.  At 96 and 120 hrs, there were significant cultivar and ripening stage impacts on larval survival. In fully-ripe fruit, no further significant mortality happened after the first instar. However, in colour-break fruit, after the initial 1^st instar mortality, high mortality also occurred in third instar larvae.  In immature-green fruits nearly all mortality occurred during the first and second instars. The difference in timing of larval mortality with ripening stage provides indirect evidence of active fruit defense which is strongest in immature-green fruit, less in colour-break fruit and absent in fully-ripe fruit. Increased knowledge of fruit defenses against fruit flies is a starting point for developing fruit fly resistant crops.

Data set collected by dissecting tomato fruits and observation (counting) samples under streo microscope.