The within‐tree distribution of the guava fruit fly,Anastrepha striatain sour guava,Psidium friedrichsthalianumand common guava,P. guajavain the seasonal highlands and non‐seasonal lowlands of Costa Rica, was examined in relation to host fruit distribution, temperature, and ambient light levels. Larvae and adult flies were significantly more abundant in the middle and lower parts of trees than in the upper canopy layer where temperatures inside sun‐exposed, potential host fruits reached lethal levels for eggs and larvae ofA. striata.The number of adult flies was also significantly greater in relatively compact foliage than in fairly open foliage of host trees. The results suggest that the foliage structure of host trees, through its influences on the temperature inside host fruits, is determining the within‐tree distribution ofAnastrephafruit flies.