Abstract: 【Objective】 To clarify the interspecific competition mechanisms and oviposition selection behaviors of Zeugodacus cucurbitae and Zeugodacus tau on shared hosts， which could provide theoretical basis for developing behavior interference-based green control strategies for fruit flies. 【Method】 Under indoor conditions， pumpkin was used as the host. Heterospecific fruit flies mixture treatment different adult densities （10， 20， and 40 pairs， with ratios of Zeugodacus cucurbitae and Zeugodacus tau being 5∶5， 10∶10， and 20∶20） were established， and conspecific fruit flies mixture treatments at the same densities served as controls. The number of attacks was recorded， and the number of emerged offspring adults was counted after female oviposition. Six egg-density gradients （100-150 eggs， 200-250 eggs， 400-450 eggs， 600-650 eggs， 800-850 eggs， and 1000-1050 eggs） were set up to analyze the inhibitory effect of initial egg load in the host by conspecific or heterospecific fruit flies on female oviposition behavior， with no egg （0 egg） as control. Furthermore， the effects of egg developmental time （1-4 d）， larval density （10-160 larvae）， and larval instar （1^st-3^rd instar） on female oviposition choice were examined，with no egg or no larva sa control. 【Result】 In heterospecific fruit flies mixture treatment， both fruit fly species showed higher attack frequencies than in the conspecific fruit flies mixture control， with Zeugodacus tau exhibiting stronger aggressiveness； at the density of 40 pairs of heterospecific fruit flies mixture， the attack frequency of Zeugodacus tau reached 53.00 times. Obvious interspecific oviposition competition was observed between the two species. The number of emerged offspring adults of two fruit flies in heterospecific fruit flies mixture treatment was significantly lower than that in conspecific fruit flies mixture control （P<0.05， the same below）， and Zeugodacus tau accounted for 61.00%-86.63% of emerged offspring in the heterospecific fruit flies mixture treatment， demonstrating a clear competitive advantage. When the initial egg load by conspecific or heterospecific fruit flies in the host reached 400-450 eggs， the continued oviposition behavior of both species was significantly suppressed， indicating that both species could recognize the egg load in the host and adjust their oviposition accordingly. The inhibitory effect of larvae in host on female oviposition was stronger than that of eggs. When eggs in host had developed for 3 d， most had hatched into larvae， and egg number of both species dropped sharply compared with the egg stage at 1-2 d； at 4 d of egg development （2^nd instar larvae）， both species almost ceased oviposition. The inhibitory effect on female oviposition increased with increasing larval density and instar. 【Conclusion】 Interspecific competition suppresses population establishment of both Zeugodacus cucurbitae and Zeugodacus tau on pumpkin， with Zeugodacus tau showing a marked competitive advantage. Both species can regulate their oviposition behavior according to the egg number in the host， and the presence of larvae in the host exerts strong inhibitory effect on female oviposition， which intensifies with increasing larval density and instar.