HOST SPECIFICITY OF FIG WASPS (AGAONIDAE).

Abstract

For the development of seeds, the figs (Ficus spp.) are dependent upon small chalcidoid wasps of the family Agaonidae. No other means of pollination of fig flowers is available to the plant, and the wasps cannot develop anywhere except in the flowers of the fig.2 There has been considerable difference of opinion as to the degree of host specificity of the fig pollinators. For example, Baker (1961) did not fully accept the specificity of fig wasps, but in a later publication Baker and Hurd (1968) said that in the enormous genus Ficus a unique situation prevails in which almost every species of fig has a recognizably different wasp as a pollinator. The present paper evaluates the evidence concerning such specificity and its occasional breakdown. The female agaonids carrying pollen enter the young receptacles at the time the female flowers are ready for pollination (female phase). Wasps probably first pollinate all the female flowers (shortand long-styled) and next lay eggs in the short-styled ones. The flowers which are only pollinated develop normally and each produces a seed, while the pollinated flowers which also received agaonid eggs become gall flowers, each nourishing a single wasp larva. The agaonid wasps reach maturity in a male-phase fig. Copulation takes place before the females escape from the galls inside the fig. After copulation, the females emerge from the galls and immediately go to the anthers, which become ripe synchronously with the softening of the fig and the emergence of the wasps inside of it. There is a difference in the way the wasps pick up the pollen from the anthers in the two subgenera of figs that reach the New World, Urostigma and Pharmacosycea. In Urostigma, exclusively pollinated by Blastophaga (Pegoscapus), the females emerge from their galls and at once go to the dehisced anthers. They pick out the pollen from the anthers using the mandibles and front legs, and move it to corbiculae or concavities located in the front coxae and in the mesosternum (Ramirez, 1969; see also Galil and Eisikowitch, 1968b and Galil and Snitzer-Pasternak, in press, for Ficus religiosa). Once the corbiculae are filled, the wasps go to exits made by the males through the fig wall and fly away. The pollen of most New World Urostigma is not shed from the anthers without wasp activity because the pollen sacs do not open sufficiently. In Pharmacosycea figs of the New World, which are exclusively pollinated by species of Tetrapus, the anthers dehisce and shed the pollen naturally and apparently without the help of the wasps; the wasps which are emerging from the galls inside the fig become completely dusted with it. They also eat it before leaving the fig. Once the newly emerged female wasps, dusted with pollen or carrying it in the corbiculae, escape from their ripe figs, they fly to another fig tree of the same species in which they developed and which pos1 Contribution number 1451 from the Department of Entomology, University of Kansas, Lawrence, Kansas. 2 Galil and Eisikowitch (1968a) divide the developmental phases of a syconium in a way which I have followed, thus: Phase A (Prefemale): young syconium prior to the opening of the ostiole. Phase B (Female): ostiolar scales loosen, female flowers ripen, agaonid and other sycophilous wasps penetrate into the syconium and oviposit into the ovaries. Phase C (Interfloral): wasp larvae and fig embryos develop. Ovaries occupied by the larvae are transformed into galls. Phase D (Male): male flowers mature, wasps reach the adult stage, fertilized female wasps leave the syconia via channels bored by the males. Phase E (Post-floral): both the syconia and the seeds inside them ripen.