Effects of age, diet, female density, and the host resource on egg load inAnastrepha ludens and Anastrepha obliqua (Diptera : Tephritidae)

Oocyte counts, used as a measure of egg load, were compared among three dif ferent age groups (15, 30 and 45 days) of two polyphagous species of tephri tid fruit flies, Anastrepha ludens and Anastrepha obliqua, which were expos ed to varying conditions of diet (sucrose vs sucrose and protein), availabi lity of oviposition substrate (present vs absent), adult female density (1, 2 and 4 females/cage), and semiochemical context (presence vs absence of m ale pheromones and fruit volatiles). In both species, oocyte counts were hi gher in older females and for females fed sucrose and protein than for fema les fed sucrose only. The presence of artificial oviposition substrates inf luenced oocyte counts in A. obliqua, but not in A. ludens. Female density i nfluenced oocyte counts in both species. Females maintained in groups had h igher egg loads than isolated females. Finally, preliminary evidence sugges ts that semiochemical context influenced oocyte counts. Counts were highest for females in a room containing both fruit volatiles and male pheromone, lowest for females in a room containing neither volatiles nor pheromone, an d intermediate for females in rooms containing either volatiles or pheromon e but not both. Our results suggest that egg load is influenced by environm ental factors in different ways in these two species. Egg load in A. obliqu a, a species whose host fruits are highly ephemeral, is responsive to acces s to the host resource. By contrast, in A. ludens, a species infesting less ephemeral fruit, female density and age played a more important role than host stimuli. The role of ovarian maturation and oviposition in mediating t hese effects, as well as implications for mass rearing and pest management, are discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.