Why do guava fruit flies, Anastrepha striata (Tephritidae), avoid the upper canopy of host trees?
The within-tree distribution of Anastrepha striata in sour guava, Psidium friedrichsthalianum, and common guava, P. guajava, in the seasonal highlands and non-seasonal lowlands of Costa Rica, was examined in relation to host fruit distribution, temperature and ambient light levels, during 1987-89. Larvae and adults were significantly more abundant in the middle and lower parts of trees than in the upper canopy layer where temperatures inside sun-exposed fruits reached lethal levels for eggs and larvae. The number of adults was also significantly greater in relatively compact foliage than in fairly open foliage of host trees. It is suggested that the foliage structure of host trees, through its influences on the temperature inside host fruits, determines the within-tree distribution of A. striata.