RESOURCE DEFENSE MATING SYSTEM IN ANTLERED FLIES, PHYTALMIA SPP (DIPTERA, TEPHRITIDAE)

Tropical rain forest flies in the genus Phytalmia exhibit a resource d efense mating system. Males possess lateral projections from the head resembling antlers, and these play a role in contests over access to o viposition sites at the larval substrate. Females arriving al these gu arded locations must mate with resident males before depositing eggs, The larval substrate consists of rotting sapwood within downed trees o r branches. Experiments in which various tree species were made availa ble within the Phytalmia habitat revealed a limited number of host pla nt species. Guarded oviposition sites were fewer than the number of ma les present, and individual sites remained attractive for only 3 d on average. Sea ratios of 3 Phytalmia species were all male-biased at the ir respective oviposition substrates. Daily censuses of marked Phytalm ia mouldsi McAlpine & Schneider revealed different visitation patterns for males and females. Male-male interactions were frequent and diffe red between species in ways related to interspecific morphological dif ferences. Successful territorial males mated multiply as did females. Following copulation, males of P. mouldsi and Phytalmia alcicornis (Sa unders) remained amplexed with females and guarded them as they ovipos ited, whereas Phytalmia cervicornis Gerstaecker males dismounted befor e any eggs were laid. The mating behaviors are discussed in the contes t of mating system theory with respect to the ecology of these species .