Gall Flowers In Figs

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Gall Flowers In Figs

Does The Fig Wasp Really Produce A Gall?

Although some authors refer to the "fruit-like" structures on wild fig trees (Ficus) as galls, they are actually specialized structures called syconia bearing minute male and female flowers on the inside. A tiny female wasp enters an opening (ostiole) on the syconium to pollinate the flowers and lay her eggs inside the short-style female flowers. She inserts her ovipositor down the stylar canal and deposits an egg inside the ovary of each short-style flower. According to I.J. Condit (The Fig, 1947), oviposition injures the stylar canal, thus inhibiting pollen tube growth and fertilization in short-style flowers. Because her ovipositor is too short, the fig wasp is unable to oviposit inside the long-style flowers. The latter flowers each develop a seed (with an embryo and endosperm) by normal pollination and double fertilization. Although there is considerable disagreement in the literature, many authors continue to describe the short-style flowers as "gall flowers," presumably because they are commonly occupied by a developing male or female fig wasp; however, they are fully capable of producing normal seed-bearing drupelets, and in this respect are no different from long-style flowers. In 2-3 months a new crop of male and female wasps emerge from the short-style flowers. In some species, such as the rustyleaf fig (F. rubiginosa), after insemination by males, the fertile female wasps pack their pollen baskets (corbiculae) with pollen and exit the syconium. These syconia serve as "wasp condos" for populations of wasps that pollinate the fig flowers in one of nature's most remarkable and complex symbiotic cycles. They also produce seeds inside long-style flowers that provide the vital genetic diversity and perpetuation of fig trees.

For a more detailed step-by-step account of pollination in a monoecious fig:
Please refer to: The Fig and Fig Wasp Scenario.
The pollination of fig flowers by symbiotic wasps is complicated and there
are several different pollination patterns in monoecious and dioecious figs.
Please refer to: Pollination Patterns In Dioecious Figs.

Minute fig wasps (Eupristina verticillata) emerging from ripe syconia of the Indian laurel fig (Ficus microcarpa). These spherical structures are not wasp galls--they are fleshy, hollow structures lined on the inside with numerous tiny flowers. The syconia serve as "condos" for species-specific symbiotic wasps that pollinate the internal female flowers.

Syconia of Ficus sycomorus. These structures are NOT galls. They are fleshy structures lined on the inside with hundreds of tiny male and female flowers. They are essentially an inside-out flower cluster (inflorescence). The syconium in center has been sectioned to show the numerous flowers on the inside. Although this species of fig has its own pollinator wasp (Ceratosolen arabicus), there is also a nonpollinator wasp Sycophaga sycomori that lays eggs inside the short-style flowers. Oviposition and the presence of nonpollinator wasp larvae not only initiate the development of endosperm tissue, but also the enlargement and ripening of the syconium containing wasp-bearing drupelets without pollination. Since the normal course of events is to abort unpollinated syconia, the entire syconium could be viewed as a gall occupied by nonpollinator wasps.

A close-up view inside of the rustyleaf fig syconium (Ficus rubiginosa) showing numerous minute male and female flowers. The female flowers are pollinated by a tiny pregnant (gravid) female fig wasp (Pleistodontes imperialis) that enters the syconium through an opening at one end (the upper end in photo). This fig species in monoecious, with male flowers, long-style and short-style female flowers in the same syconium.

Minute flowers inside monoecious syconium of the Baja California wild fig (Ficus palmeri). Left, male flower showing a single stamen (anther) protruding from the calyx. Center and right, short and long-style female flowers consisting of a single pistil protruding from the bract-like calyx.

Magnified view of a male and female fig wasp (Pleistodontes imperialis) from the rustyleaf fig (Ficus rubiginosa) next to the "eye" of an ordinary sewing needle. The smaller, wingless male has an amber body and black head with greatly reduced eyes.

See Straight Pin & Sewing Needle Used In Wayne's Word Articles

Minute flowers from the dioecious syconia of the common edible fig (Ficus carica). Left, male flower showing 5 stamens protruding from bract-like calyx. Center and right, short and long-style female flowers consisting of a single pistil protruding from bract-like calyx. The long-style female flowers are produced in syconia on separate "female" trees, while the male flowers and short-style female flowers are produced in syconia on "male" caprifig trees.

The "gall controversy" of fig flowers is complicated because food tissue (endosperm) for the developing larva may be initiated parthenogenetically (without pollination and fertilization), possibly by a mechanical or chemical stimulus during oviposition. In this case the flower functions like a minute gall, except there is no apparent tissue malformation as in typical insect galls. Functional male caprifigs of Ficus carica produce three crops of syconia per year: the summer profichi, fall mammoni and overwintering mamme that mature the following spring. Only the profichi crop produces pollen, and this is used to pollinate the Calimyrna orchards of California's Central Valley. The receptive mamme and profichi syconia are not pollinated, so endosperm tissue to nourish the wasp larvae in these crops must be initiated parthenogenetically. Whether they contain a mature seed or a wasp, the short-style flowers of caprifigs appear virtually identical in structure, and do not fit the definition of a typical gall. However, proponents of gall flower terminology argue that when the wasp induces the formation of nutritive endosperm tissue, the ovary interior is literally transformed into a minute gall.

A fig wasp larva inside the ovary of a short-style female flower in an overwintering mamme syconium. This is the leafless dormant season for the caprifig (Ficus carica). The larva fed on parthenogenetic endosperm tissue that developed without pollination. The initiation of endosperm tissue after oviposition by the female wasp meets the criterion for gall formation. The larvae consumes the galled tissue within the ovary wall. After metamorphosis, the adult male wasp chews a hole through the ovary wall and exits the female flower. He crawls to another short-style female flower that contains a mature female wasp. He climbs up on the ovary of the flower, bites a fertilization hole in the ovary wall, and inserts his long, slender abdomen into the opening, thus inseminating the female. After being inseminated, the female crawls out of the fertilization hole through the ovary wall initially made by the male. Wasp larva photographed in January 2009.

Many of the crowded ovaries inside this dried mamme syconium have been hollowed out by wasp larvae. The larvae fed on the galled endosperm tissue inside, leaving the endocarp layer of the inner ovary wall. These empty shells are not seeds. They are hollowed out drupelets from the numerous short-style female flowers.

Magnified view inside a freshly-picked mamme syconium (16 Jan. 2009) showing crowded ovaries of short-style female flowers (gall flowers). Some of the ovaries contain wasp larvae (blue x's) which have consumed the contents of the endocarps.

Magnified view inside syconium of Ficus rubiginosa showing two male and two female fig wasps (Pleistodontes imperialis). The smaller males (left) have a black head and amber-colored, wingless body. The winged females (right) are larger with longer antennae. In this image, the inseminated females have imerged from their individual flowers and are ready to escape from the syconium.

Iziko Museums of Capetown: How Fig Wasps Are Pollinated

Another case for wasp-induced "gall-like" endosperm tissue is the sycomore fig (Ficus sycomorus) of the Near and Middle East. According to J. Galil (Endeavor, Vol 1, 1977), oviposition by the nonpollinator wasp Sycophaga sycomori results in the development of parthenogenetic endosperm tissue which the larva feeds upon. The galled endosperm tissue develops through proliferation of nucellar cells surrounding the embryo sac. Since there is no pollination, the syconia are seedless. However, in its native habitat of eastern Central Africa and Yemen, F. sycomorus is pollinated by the symbiotic wasp Ceratosolen arabicus, and the long-style flowers produce seeds. The story is even more complicated because without pollination the sycomore fig typically drops its immature syconia. Oviposition and the presence of nonpollinator wasp larvae not only initiate the development of endosperm tissue, but also the enlargement and ripening of the syconium containing wasp-bearing drupelets without pollination--a condition known as parthenocarpy. Since the normal course of events is to abort unpollinated syconia, the entire syconium could be viewed as a gall occupied by nonpollinator wasps.

The sycomore fig was carried north to Egypt by 3000 B.C., and on to Israel, Lebanon and Cyprus. Early farmers in these regions learned how to induce parthenocarpy in sycomore figs by gashing them with a knife. Within 3-4 days the hard, green syconia enlarge and become sweet and fleshy, long before any possible wasp inhabitants are sufficiently developed to damage the crop. In fact, some biblical scholars think the phrase "gatherer of sycomore fruit" (Amos 7:14) actually means "piercer of sycomore fruit." According to J. Galil (Economic Botany Vol. 22, 1968), gashed figs produce ethylene gas which hastens the ripening process. It is interesting to note that in Israel today there is a fully parthenocarpic variety of sycomore fig that does not require gashing or wasps. The syconia ripen on the tree without any external stimulus, as in the popular black mission, kadota and brown turkey varieties of F. carica.

Which Figs Grew In The Ancient Holy Land?

An excellent article entitled "The History of the Fig in the Holy Land from Ancient Times to the Present" was written by Asaph Goor in Economic Botany 19: 124-135 (1965). The fig species discussed by Goor is the common edible fig (Ficus carica). This tree was cultivated for its fruit more than 5,000 years ago and is native to the region between the Mediterranean and Black Seas, sometimes referred to as the ancient region of Caria in Asia Minor. It is a dioecious species with separate male and female trees, and a symbiotic pollinator wasp (Blastophaga psenes) that is propagated inside the fruits (syconia) of male trees called caprifigs. It grows wild over a large area, including southern Europe and the Middle East. Goor (1965) stated that Ficus carica grew wild in the Holy Land thousands of years ago; however, this doesn't necessarily mean that it was truly native (indigenous) to the Holy Land. It may have been introduced by people to this region, either by seeds or cuttings. Ficus carica and its symbiotic wasp have even been introduced into California, including male and female trees that grow wild in San Diego County. In fact, the symbiotic wasps live at the Wayne's Word headquarters in a caprifig that produces three crops of inedible figs (syconia) each year, including a wasp-bearing, overwintering mamme crop that remains on the bare branches when the tree is devoid of leaves. There are several varieties of male caprifigs and hundreds of varieties of female Ficus carica trees, some of which develop delicious, seedless, parthenocarpic fruits that do not require pollination. There are also varieties in which the female trees will shed their entire crop if they are not pollinated by the symbiotic fig wasp. These varieties have been selected by people over countless centuries. The trees are readily propagated by cuttings and were transported and cultivated by people thousands of years ago. Apparently many ancient civilizations were aware of the fact that Ficus carica required pollination in order to produce edible, seed-bearing fruits, a process called caprification. In 350 B.C., Aristotle described fig wasps that came out of caprifigs and penetrated the unripe female fig fruits, thus fertilizing them. Theophrastus (372?-287? B.C.) discussed caprification in detail, and Pliny (23-79 A.D.) devoted an entire chapter to the practice of caprification in Italy. The subject of fig pollination and "gallflies" in ancient Babylonia is also mentioned by Herodotus (Book I, 485?-425? B.C.). Early horticulturists were undoubtedly aware that the seeds impart a superior, nutty flavor to the fruit, and in some varieties the fruit will not set if it is not pollinated by fig wasps. The fig referred to in ancient Babylonia was probably Ficus carica, but another species called the sycomore fig (Ficus sycomorus) was also used for food in the eastern Mediterranean region. According to Goor (1965): "The sycomore fruit is much inferior and cheaper... It is eaten by the poorer classes and by shepherds in plains where it grows alone." In addition it does not survive cold winters like Ficus carica, and Ficus carica has a much wider range, particularly in colder regions of Iraq and northward.

Another excellent article about ancient fig cultivation was written by J. Galil entitled "An Ancient Technique for Ripening Sycomore Fruit in East-Mediterranean Countries" (Economic Botany 22: 178-190, 1978). When the term "fig gashing" in the Near and Middle East is mentioned in various articles and books (including the Bible), it most likely refers to the sycomore fig (Ficus sycomorus), a species that is actually native to eastern Central Africa. Although the true East African pollinator wasp is not present in the Holy Land, an ovipositing, nonpollinator wasp does induce parthenocarpic fruits containing wasps instead of seeds. The ancient technique of gashing also induces edible, parthenocarpic fig fruits that enlarge and ripen rapidly before the wasps inside mature.

Bogus Fig Wasps With Very Long Ovipositors

The presence of remarkably specific pollinator wasps probably accounts for the lack of hybridization between many tropical fig species, even though they grow close together in the rain forest. With an abundant supply of specific pollinators for each tree, several species of figs can coexist side-by-side, a phenomenon known as "species packing." Fig wasps apparently do not enter the "wrong" syconium, possibly due to a special chemical attractant for each species of wasp. As with most complex biological phenomena, there are always exceptions. Some syconia may contain more than one species of wasp, including "bogus" fig wasps of the families Torymidae and Eurytomidae, which have very long ovipositors. Some torymid wasps can even oviposit through the syconium wall without ever entering or pollinating the fig. Other bogus fig wasps may simply insert their long ovipositors into long-style flowers which are normally reserved for fig seeds and not fig wasps. The torymid larvae may be seed predators, parasites of fig wasp (agaonid) larvae, or inquilines coexisting with, but not necessarily harmful to the fig or its symbiotic wasp. With its very long ovipositor, the bogus fig wasp is essentially beating the system of long-style female flowers which prohibit egg laying (oviposition) by typical symbiotic pollinator wasps. The presence of nonpollinator, bogus fig wasps and natural pollinator wasps in the same syconium is a complex and perplexing coevolutionary problem in fig biology.

Bogus fig wasps (family Torymidae and Eurytomidae) have an unusually long ovipositor. It can easily penetrate the long-style flowers which are too long for true female fig wasps. Thus bogus fig wasps can lay eggs in long-style fig flowers reserved for fig seeds. Consequently no seeds are produced in these flowers. In addition, the bogus fig wasps do not pollinate fig flowers. Although they do not benefit the fig tree, torymid and eurytomid wasps are common inhabitants of New World fig syconia. Their coexistence with natural fig pollinator wasps is a complex and perplexing coevolutionary problem in fig biology.

How Ancient Are Figs (Ficus) In The Geologic Record?

A 34 million-year-old fossil fig wasp from the Eocene was dicovered in limestone on the Isle of Wight, England (Stephen Compton et al. 2010). It was originally thought to be a tiny winged ant, but was later confirmed to be a female fig wasp because of the pair of pollen baskets (corbiculae) on the underside of its thorax. The corbiculae of this wasp named Ponera minuta even contained Ficus pollen. The previous record for ancient fig wasps was 23 million-year-old Dominican Republic amber from the Miocene. DNA phylogenetic analysis indicates that the fig and fig wasp relationship may extend back more than 65 million years ago to the Cretaceous Period. The Isle of Wight fig wasp is relatively unchanged compared with present-day fig wasps of the family Agaonidae. "No innovations in the relationship are discernible for the last tens of millions of years." According to Nefdt and Compton (1996) short-style female flowers in moneous figs have longer styles than those in male figs of dioecius species. The shorter ovipositor of Ponera minuta indicates that its symbiotic host was dioecious, an advanced reproductive pattern in fig evolution.

Fossil leaves embedded in 60 million-year-old limestone from the Fort Union Formation near Glendive, Montana have tentatively been identified as Ficus. Fossil fig syconia named Ficus ceratops from the 70 million-year-old Hell Creek Formation in this area have been clearly shown to be a different species, possibly an extinct palm.

Fossil Fig Syconia In Wyoming & Montana?

Fossilized (petrified) fig syconia are very difficult to find because they decay rapidy. In 1881, a remarkable discovery was made in the Lance Formation of Converse County, Wyoming by J.B. Hatcher. The syconia had the perfect shape of a modern fig, with a narrowed neck region and a globose body. In fact, they were originally thought to be bulbs of a monocotyledonous plant. Most of the peduncles were broken, but an entrance to the interior (ostiole) at the opposite end was visible on some of the syconia. According to F.H. Knowlton (Bulletin of the Torrey Botanical Club Vol. 38) who described this species in 1911, the interior cavity was filled with course sandstone mixed with extraneous matter, such as bits of vegetation and fragments of shells. According to Knowlton (1911): "In no case was the cavity found to contain seeds, which seems rather remarkable considering the fine state of preservation of the fruit as a whole. It seems probable that when the neck was broken the larger, globose end, being heavier, floated downward and the fruits were filled and covered up in this upright position in which they are found." Actually in modern figs (called syconia), the neck is attached to a stalk (peduncle).

The fossil fig was named Ficus ceratops by F.H. Knowlton (1911). The type locality where the original specimen was collected is also called "Ceratops Beds" because of the abundant fossils of late Cretaceous horned (ceratopsid) dinosaurs. These dinosaurs include the well-known Triceratops made popular in the movie Jurassic Park. It weighed up to 12 tons, larger than an elephant. It was armed with huge horns over one meter long and an enormous parrot-like beak with an incredibly strong bite force. Undoubtedy it needed this armor to defend itself against T-Rex that also roamed this region. Incidentally, Knowlton also named the Triassic conifer Araucarioxylon arizonicum in 1889, the state fossil of Arizona.

Petrified "fig syconia" from the badlands of eastern Montana (Dawson County). They were originally thought to be from an extinct species of fig (Ficus ceratops) dating back to the late Cretaceous Period (70 million years ago). Tracks and fossils of T-Rex have also been found in this region of Montana. Right: One of these so-called "fig syconia" is 70 million years old! The other two are dried Mission and Calimyrna figs purchased at a nearby grocery store. Note: The fine longitudinal striations are not characteristic of fig syconia. In fact, these "fig syconia" might actually be endocarps of an extinct palm. See following explanation:

Ficus ceratops Is Not A Fig!

Astrocaryum huicungo
Like so many other aspects of fig biology, even the identification of fossil syconia is controversial. Several authors have suggested that some of the fig-like fossils from the Hell Creek Formation might belong to a different plant family. According to Alan Graham (1962), the fossil syconia differ from fig fruits is several respects: "The 2-layered pericarp wall, coarse striations at the base of the globose portion of the specimens, and the collar at the proximal end of the stalk are not characteristic of Ficus fruits. These morphological features are evident, however, on fruits of Guarea (Melicaeae)." Elisabeth McIver (2002) has studied these "figs" associated with fossils of Tyrannosaurus rex from southwestern Saskatchewan, Canada. She has transferred them to the new taxon Spinifructus antiquus of an unknown family and order. She suggested that they may be from an arecoid palm with pear-shaped fruits similar to the genera Astrocaryum, Asterogyne or Barcella.

The above image shows the large seed-bearing fruits and endocarps of the starnut palm (Astrocaryum huicungo) from the Rio Napo, a tributary of the Amazon River in Ecuador. This palm is named from the starlike design surrounding the three germination pores an the wide end of endocarps. They have the fibrous longitudinal striations and general shape of Spinifructus. The apex of endocarps have three distinct germination pores that are not visible on the fossil Spinifructus antiquus (syn. Ficus ceratops). These palm fruits are produced in dense clusters.

Phytelephas aequatorialis

Astrocaryum alatum

Palm Fruits With Pointed Projections & Spines

Elisabeth McIver (2002) suggested that the fruits of Spinifructus antiquus might be similar to palms of the genus Astrocaryum. In his on-line article entitled "Dangerous Palms," Geoff Stein has a image of the spine-covered fruits of Astrocaryum alatum (upper right).

See "Dangerous Palms" By Geoff Stein

The preconceived stereotype of a fig is something resembling a pear-shaped edible fig (Ficus carica) or dried figs at the supermarket. This is the mistake I made when I first saw these permineralized fruits. Actually, most of the species of wild tropical figs that I have seen have smaller globose syconia. In addition, fig syconia have very little woody tissue and rot away quickly. Fresh edible figs have a very short shelf life and are commonly dried. Palm fruits occur in large, dense clusters and this would explain the occurence of numerous Spinifructus in one small chunk of ground. In addition, fruits of palms such as Astrocaryum are very fibrous with hard, woody endocarps that would permineralize well (i.e. the contents of lignified cells become replaced by minerals and the fruit literally turns into stone). The presence of spines on the outer pericarp rules out figs. It is interesting that the original description by J.W. Dawson (1875) mentions the spiny outer wall.

The first published name for this fossil "fig" was Aesculus antiquus because the original author J.W. Dawson thought it resembled an ancient species of Aesculus (horsechesnut or buckeye) in 1875. See the horsechestnut fruit (left) photographed in Montana. Apparently most of the fossils don't have the spiny fruit wall. With an outer spiny pericarp, this fossil simply cannot be a fig syconium (Ficus). Knowlton did not cite Dawson in his 1911 paper where he describes Ficus ceratops. He was apparently unaware of the spiny outer wall on this fruit. Since Dawson's name predates Knowlton's Ficus ceratops, Dawson becomes the parenthetical author and Elizabeth McIver becomes the new author: Spinifructus antiquus (Dawson) McIver.

Like Knowlton's logs of Petrified Forest National Park (Araucarioxylon arizonicum) that were renamed Pullisilvaxylon arizonicum by R. A. Savidge in 2007, Knowlton's infamous Ficus ceratops has also been renamed by E. McIver in 2002.

A Taxonomic Problem With Araucarioxylon arizonicum

A 60 million-year-old fig leaf embedded in hard-rock limestone from the Fort Union Formation near Glendive, Montana. This fossil-rich strata is from the Paleocene Epoch that immediately followed the mass extinction event of dinosaurs at the end of the Cretaceous Period, known as the K-T boundary (Cretaceous-Tertiary boundary). The term Paleocene ("early-recent") refers to a time period when dinosaurs were replaced by smaller mammals, long before modern mammalian orders emerged. The best explanation (scientific theoery) for the demise of non-avian dinosaurs is an enormous 10 km (6 mile) diameter asteroid that collided with the earth causing a global dust cloud that blotted out the sun for many months. Estimates as high as 85 percent of all species disappeared from the face of the earth at this time. This catastrophic event forever changed the direction of the evolution of life on earth.

The K-T boundary is clearly visible in Makoshika Stae Park near Glendive, Montana. It is a dark, narrow band of sediments and carbonized plant material (coal) that separates the Cretaceous and Tertiary periods about 65 million years ago. The tan strata above the K-T band is called the Fort Union Formation. It is younger than 65 million years and does not contain dinosaur fossils. Below the K-T band is the older brownish-gray Hell Creek Formation that is rich in dinosaur fossils, including Tyrannosaurus rex, Triceratops, the amazing duck-billed Hadrosaurus, and the so-called petrified "figs" (Spinifructus antiquuas).

In 1980, a team of researchers consisting of Nobel prize-winning physicist Luis Alvarez, his son, geologist Walter Alvarez, and chemists Frank Asaro and Helen Michels discovered that sedimentary layers found all over the world at the K-T boundary contain a concentration of iridium many times greater than normal. Iridium is a rare earth element that is abundant in most asteroids and comets. It is the second densest element after osmium and the most corrosion-resistant metal. The Alvarez team suggested that an asteroid struck the earth at the time of the K-T boundary.

Above the 65 million year old K-T boundary is the Fort Union Formation & below is the Hell Creek Formation.

Fossil fig leaves have also been reported from the Madro-Tertiary Geoflora in California by Daniel Axelrod (1958). This habitat consisted of semiarid live oak-conifer woodland, chaparral and grassland. Ira Condit (The Fig, 1947) received the following letter from famous paleobotanist Ralph Chaney in 1943: "I have seen a leaf of the carica type from the Miocene of southern California and have no doubt that its relationship to F. carica is extremely close."

Other WAYNE'S WORD Articles About Figs And Their Wasps:

The Fig/Fig Wasp Relationship
Pollination Patterns In Dioecious Figs
Sexuality In Figs And Other Flowering Plants
Figs Of The Holy Land (Their Role In World Religions)

References

Armstrong, W.P. 1995. "To Be Or Not To Be A Gall." Pacific Horticulture 56: 39-45.

Armstrong, W.P. 1988. "The Calimyrna Fig and Its Wasp." California Garden 79: 135-138.

Armstrong, W.P. and S. Disparti. 1988. "Wild Figs and Wasps of the Californias." Environment Southwest No. 521: 7-11.

Condit, I.J. 1947. The Fig. Chronica Botanica Co., Waltham, Mass.

Condit, I.J. and S.E. Flanders. 1945. "Gall-Flower of the Fig, A Misnomer." Science 102 (2640): 128-130.

Galil, J. 1977. "Fig Biology." Endeavour 1: 52-56.

Galil, J. 1968. "An Ancient Technique for Ripening Sycomore Fruit in East-Mediterranean Countries." Economic Botany 22: 178-190.

Galil, J. 1967. "Sycomore Wasps From Ancient Egyptian Tombs." Israel Journal of Entomology II: 1-10.

Galil, J. and D. Eisikovitch. 1974. "Further Studies On Pollination Ecology in Ficus sycomorus. II. Pocket Filling and Emptying by Ceratosolen arabicus." Magr. New Phytol.. 73: 515-528.

Goor, A. 1965. "The History of the Fig in the Holy Land from Ancient Times to the Present." Economic Botany 19: 124-135.

Ramirez, W. 1969. "Fig Wasps: Mechanism of Pollen Transfer." Science 163: 580-581.

Ramirez, W. 1974. "Coevolution of Ficus and Agaonidae." Annals of the Missouri Botanical Garden 61: 770-780.

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