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The fruit fly, Bactrocera tau (Walker) (Diptera: Tephritidae), is an important pest of fruit and vegetable crops. In this study, host preference of B. tau females and the effects of host species and larval density on larval survival, pupal weight, adult emergence, and developmental duration were investigated on cucumber (Cucumis sativus L.), sponge gourd (Luffa cylindrical L. (Roem)), bitter gourd [Momordica charantia (Cucurbitaceae) L.], guava [Psidium guajava (Myrtaceae) L.], and tangerine [Citrus reticulata (Rutaceae) (Blanco)]. The results showed that females preferred to cucumber over other host species. Larval feeding experience affected subsequent host oviposition preference of adult females. Host species and initial larval density affected certain aspects of the biology of B. tau. Larval density negatively affected insect performance. Survival rates at low densities were significantly higher than that at high densities. Total developmental duration reduced at high larval densities. Cucumber was more suitable to larval growth. Larvae on cucumber grew faster and the puparia were heavier than that on other host species. Larval survival, pupation rate and adult emergence were higher on cucumber compared with those in other host species. Oviposition preference of adult females was correlated with performance of their offspring.

The melon fly, Bactrocera cucurbitae (Coquillett), and the pumpkin fly, Bactrocera tau (Walker), are economically important pests that attack mainly cucurbitacean fruits. The two fruit fly species have similar natural distributions, host ranges, and population growth capacities. This study was designed to assess the asymmetrical competitions through resource exploitation between the larvae of B. cucurbitae and B. tau at different density levels and temperatures, and on different hosts by comparing the relative effects of interspecific and intraspecific interactions on four life history parameters: survival rate, puparial mass, puparial duration, and developmental duration. Our results showed that intraspecific and interspecific competitions occurred under some laboratory conditions, and B. cucurbitae took advantage over B. tau at the high-density level and at low and high temperatures on pumpkin, bitter gourd, and bottle gourd when interspecific competition took place. Intraspecific and interspecific competitions mainly affected the puparial mass and the survival rate of the two fruit fly species but had no marked effect on the puparial duration or development duration.

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