Fig wasp

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Fig wasps
Blastophaga psenes
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Suborder: Apocrita
Superfamily: Chalcidoidea

Fig wasps are wasps of the superfamily Chalcidoidea which spend their larval stage inside figs. They can be the pollinating fig wasps or parasitic wasps. The parasitic wasps belong to several groups of the superfamily Chalcidoidea. While the pollinating fig wasps are galler, the parasitic fig wasps display a great range of feeding regime from carnivory (parasitoid wasps) or herbivory (making galls as the pollinating wasps).

Taxonomy[edit]

The fig wasps are a polyphyletic group, including several unrelated lineages whose similarities are based upon their shared association with figs; efforts are underway to resolve the matter, and remove a number of constituent groups to other families, particularly the Pteromalidae and Torymidae. Thus, the number of genera in the family is in flux. The family Agaonidae has been recently updated to include all the pollinating fig wasps[1] and the subfamily Sycophaginae.[2] The remaining families such as Epichrysomallinae, Sycoecinae, Otitesellinae, and Sycoryctinae should be included in the Pteromalidae.[2]

The female (left) and male Blastophaga psenes

Morphological adaptations[edit]

Among the Agaonidae, the female is a normal insect, while the males are mostly wingless. The males' only tasks are to mate with the females while still within the fig syconium and to chew a hole for the females to escape from the fig interior. This is the reverse of Strepsiptera and the bagworm, where the male is a normal insect and the female never leaves the host. The non-pollinating wasps have developed impressive morphological adaptations in order to oviposit eggs inside the fig but from the outside: an extremely long ovipositor.

Most fig inflorescences contain three kinds of flowers: male, short female, and long female. Female fig wasps can reach the ovaries of short female flowers with their ovipositors, but not long female flowers. Thus, the short flowers grow wasps, whereas the long flowers become seeds. In figs of this sort, the crunchy bits in the fruit contain both seeds and wasps. However, several commercial and ornamental varieties of fig are parthenocarpic and do not require pollination; these varieties are not visited by fig wasps.

Pollinating fig wasp (Ceratosolen sp.) collected on Ficus septica from South of Taiwan
Ovipositing non-pollinating fig Apocrypta on Ficus sur, Jan Celliers Park, Pretoria

Life cycle[edit]

The life cycle of the fig wasp is closely intertwined with that of the fig tree it inhabits. The wasps that inhabit a particular tree can be divided into two groups; pollinating and nonpollinating. The pollinating wasps are part of an obligate nursery pollination mutualism with the fig tree. Both life cycles of the two groups, however, are very similar.

Though the lives of individual species differ, a pollinating fig wasp life cycle is as follows. In the beginning of the cycle, a mature female pollinator wasp enters the immature "fruit" (actually a stem-like structure known as a syconium) through a small natural opening, the ostiole and deposits her eggs in the cavity. Forcing her way through the ostiole, she often loses her wings and most of her antennae. To facilitate her passage through the ostiole, the underside of the female's head is covered with short spines that provide purchase on the walls of the ostiole. In depositing her eggs, the female also deposits pollen she picked up from her original host fig. This pollinates some of the female flowers on the inside surface of the fig and allows them to mature. After the female wasp lays her eggs and follows through with pollination, she dies. After pollination, there are several species of non-pollinating wasps which deposit their eggs before the figs harden. These wasps act as parasites to either the fig or the pollinating wasps. As the fig develops, the wasp eggs hatch and develop into larvae. After going through the pupal stage, the mature male’s first act is to mate with a female. The males of many species lack wings and are unable to survive outside the fig for a sustained period of time. After mating, a male wasp begins to dig out of the fig, creating a tunnel through which the females escape.

Once out of the fig, the male wasps quickly die. The females find their way out, picking up pollen as they do. They then fly to another tree of the same species, where they deposit their eggs and allow the cycle to begin again.

Coevolution[edit]

The fig-wasp mutualism originated between 70 and 90 million years ago as the product of a unique evolutionary event.[3][4][5] Since then, cocladogenesis and coadaptation on a coarse scale between wasp genera and fig sections has been supported by both morphological and molecular studies.[5][6] This illustrates the tendency towards coradiation of figs and wasps.[5] Such strict cospeciation should result in identical phylogenetic trees for the two lineages [4] and recent work mapping fig sections onto molecular phylogenies of wasp genera and performing statistical comparisons has provided strong evidence for cospeciation at that scale.[4]

Groups of genetically well-defined pollinator wasp species coevolve in association with groups of genetically poorly defined figs.[7] The constant hybridization of the figs promotes the constant evolution of new pollinator wasp species. Host switching and pollinator host sharing may contribute to the incredible diversity of figs.[7]

Genera[edit]

Fig wasps genera and classification according to the figweb website and recent publications:[1][2][8]

Notes[edit]

References[edit]

External links[edit]