Controlled laboratory trials were conducted using Cucurbita moschata as the host to ascertain the intraspecific competitive patterns and threshold density of Zeugodacus cucurbitae. Using Logistic II modeling, the growth and development parameters of larvae at varying egg densities were investigated. To explore the connection between female size and fecundity, the daily egg-laying output of female flies of varying sizes was monitored. The results showed that Z. cucurbitae exhibited a typical pattern of exploitative competition. The Logistic II model provided an accurate prediction of larval development and changes in population density, which could be roughly divided into four phases. When the population density(x) was less than 1.803 0 eggs per 10 g fruit, pupal volume and immature mortality changed gradually. In the range of 1.803 0≤x<71.010 1 eggs per 10 g fruit, pupal volume declined significantly(experiencing 79.63% reduction compared to the gradual-change phase). When 71.010 1≤x<123.249 9 eggs per 10 g fruit, there was a sharp increase in the immature mortality(which rised by 58.14% in relation to the gradual-change phase). When x exceeded 123.249 9 eggs per 10 g fruit, all parameters stabilized. Z. cucurbitae females were not influenced by density. There was a significant positive correlation between female body size and fecundity. Larger individuals exhibited longer egg-laying period, lifespans and higher total egg outputs.