]Reprinted from MYCOLOGIA, Vol. II., No. 4, July, 18o1.]
AN IMPORTANT ENTOMOGENOUS
H. S. FAWCETT
(WITH PLATES 28 AND 29, CONTAINING FIGURES)
In 1896, H. J. Webber discovered a fungus parasite of the
citrus whitefly and described its sterile form under the name of
"Brown mealy-wing fungus (2)." It is now popularly known
by the orange growers of Florida as the "Brown fungus" of
the whitefly. The spread of this fungus on whitefly larvae,-
(I) by means of superficial hyphae that spread over the surface
of the leaves attacking every whitefly larva in their way, and
(2) by means of spore-like aggregations of cells that may be
carried in the air or by insects,-make this fungus one of the
most important parasites of the whitefly! This fungus and the
red fungus (Aschersonia Aleyrodis) are being introduced by
orange growers into many localities in Florida with the belief
that they are the most economic means yet discovered of keeping
the whitefly (Aleyrodis Citri) under control.
SPREAD OF THE FUNGUS BY ARTIFICIAL MEANS
Artificial means of spreading this fungus and Aschersonia
Aleyrodis have been developed by E. W. Berger, of the Florida
Agricultural Experiment Station (12, 13). The two most com-
monly used are the leaf-pinning method and the spore-spraying
method; the first consisting in pinning into a citrus tree fungus-
bearing leaves in contact with larva-infested leaves; the second
in spraying surfaces of leaves with water containing the spores
of the fungi. The latter method has been taken up quite ex-
tensively in some orange groves. This is shown by the fact that
at the present time there are men in Florida who make it a
regular business to spray whitefly-infested orange trees in this
way, getting their supplies of fungus spores from citrus leaves
on which the fungus has previously developed upon whitefly
larvae. Whenever the atmospheric conditions are favorable to
the growth of these fungi, fair success in checking the whitefly.
has been attained.
DEVELOPMENT OF THE FUNGUS
The fungus as it develops upon a larva of the whitefly forms a
chocolate-brown (No. io, Saccardo's Chromotaxia) stroma (pl.
28, f. 2), which to the unpracticed eye looks like the citrus red
scale (Chrysomphalis Aonidum). A good description is given
of this stage of the development of the fungus by Webber (2) as
follows: "The hyphae develop in the body of the insect, burst
out around the edges of the scale, and gradually grow up over it.
In the early stage they form a brown, compact layer around the
edge of the larva. As the fungus develops, the hyphae entirely
cover the larval scale, forming a dense, hard, and smooth stroma.
The mature stroma is compressed-hemispherical, frequently having
a slight depression in the apex over the center of the insect, where
the hyphae come together as they spread from the edge of the
scale in their development. The hyphae which make up the body
of the stroma, are light brown, very tortuous, and but slightly
branched. Those in the body of the insect are of similar char-
acter, but a much darker brown. From the base of the stroma a
ground mycelium, or hypothallus, spreads out in all directions on
the surface of the leaf, forming a compact membrane near the
stroma, but becoming gradually dispersed into separate filaments."
In the later development of the fungus, the separate filamants
spoken of by Webber as spreading for a distance of one half
inch, grow out over the entire surface of the leaf, branching only
sparingly and infecting every larva present. They extend also
around the edges and over the upper surface of the leaf. These
filamentous hyphae are colorless to slightly tawny with age.
They are only occasionally branched, forming a loose, incon-
spicuous mycelium over the surface of the leaf. On the upper
surface of the leaf, on short lateral hyphae, are borne the sporo-
dochia, which are 60 to 90go in diameter. These consist of an
aggregation of conidia-like, inflated, spherical cells, 12-18 in
diameter. From near the place of attachment of the sporo-
dochium, there radiate 3 to 5 hypha-like appendages, which are
150-200oo long by 6-8 wide, and are one- to three-septate (pl.
FAWCETT: AN IMPORTANT ENTOMOGENOUS FUNGUS 166
29, f. 5). This entire aggregation of spherical cells and append-
ages usually remains in union and functions as a spore. When
abundant, these sporodochia present to the eye the appearance of
a reddish-brown dust over the upper surface of the leaf (pl. 28,
f. i). The presence of the brown stromata may easily be known
at a distance of 10 to 20 feet by this characteristic appearance.
In most cases these sporodochia are found only on the upper sur-
face, but if the lower surface of a leaf happens to be turned over
for some time they will develop there also. This condition of
the fungus is common in the summer and fall. The sporodochia
were first noticed in the fall of 1905, and have been observed
since in great abundance every year. The supposed connection
of these sporodochia with the brown stromata was touched upon
in 1908 (15), but only recently has the connection between the
two been proved. The relation of the sporodochia to the spread
of the fungus is interesting. When mature, the sporodochium
with its accompanying appendages breaks off from the mycelium
and remains upon the surface, apparently held lightly by the
appendages. The inflated cells make it light, so that when once
detached it blows about easily, and on coming in contact with a
fairly rough surface it tends to hold fast to it. It seems probable
that the appendages may also serve to hold the sporodochia to
bodies of large insects that may drag them from one part of the
tree to another.
GERMINATION OF SPORODOCHIA
These Aegerita sporodochia when germinated in hanging-drop
cultures of sterile water and in 5 per cent. glucose solution, were
seen to produce hyphae (pl. 28, f. 3, 4) identical with those which
compose the brown stromata on the whitefly larvae. When
germinating, the first hyphae grow out either from the sporo-
dochia or from the ends of the appendages. These branch rather
sparingly, but in a few days, in 5 per cent. glucose solution, form
a network by the intercrossing of the branches (pl. 28, f. 4).
INOCULATIONS OF WHITEFLY LARVAE
Four different attempts were made to inoculate larvae of white-
fly with these sporodochia, three of which were successful. One
of these is here given in detail. The sporodochia were carefully
picked off one by one under the compound microscope. A
camel's hair brush moistened with water containing these sporo-
dochia was drawn over whitefly-infested leaves on trees at Gaines-
ville, Fla., August II, 1909. No brown fungus could be found
nearer than one and one half miles from this place. In 9 days,
the young larvae showed effects of fungus infection. In 16 days,
the initial stage of the stromata were evident, bursting through
the edges of the larvae (pl. 29, f. 7). In a few weeks, the typical
brown stromata were produced, but no sporodochia were yet
evident. In two or three months, the hyphae had grown around
to the upper surface of the leaves and had produced the Aegerita
sporodochia. On more than a hundred trees not inoculated no
brown fungus developed.
Because of the economic importance of this fungus, it has
been suggested in Science that it be designated as Aegerita Web-
beri for convenience until the perfect stage is found. The form
of the hyphae strongly suggest relationship to the Hypochnaceae
of the basidiomycetous fungi, but as yet the basidia spores have
not been found. A technical description follows.
Aegerita Webberi sp. nov.
Sporodochia superficial, subglobose, whitish when young, turn-
ing to reddish-brown when mature, 60-9o p in diameter, bearing
three to five appendages; conidia-like cells globose to ellipsoid,
hyaline, inflated, thin-walled, 12-18 p in diameter, persistent,
hanging together in chains and clusters; appendages 3 to 5 in
number, straight, thick-walled, 2- to 3-septate, rounded at apex,
150-20oo0 long by 6-8 f at the base, narrowing to 4-6 p near the
apex, arising from within near the base of the sporodochium.
Fertile hyphae spreading, colorless to slightly tawny with age,
sparingly branched, distantly septate, forming a loose mycelium
on the upper surface of the leaf. Stromata pustular, chocolate-
brown, smooth, with depressed top when young, becoming convex
to flat when mature, 0.5-2 mm. in diameter, composed of inter-
crossing thick-walled hyphae; margin of stroma membranous,
gray to tawny, extending 5-15 mm. and giving rise to a wide-
Found on larvae of Aleyrodes Citri R. & H. and on A. nubifera
Berger, on the under surface of citrus leaves.
MYCOLOGIA PLATE XXVIII
5,._.- 1 ..
AEGERITA WEBBERI FAWCETT
AECERITA WEBTERI FAWCETT
FAWCETT: AN IMPORTANT ENTOMOGENOUS FUNGUS 168
I. Webber, H. J. Proc. Fla. State Hort. Soc. 1896.
2. Webber, H. J. Div. of Veg. Phys. and Path. Washington, D. C. Bull.
13: 27-30. 1897.
3. Webber, H. J. Proc. Fla. State Hort. Soc. 55-57, 70. 1897.
4. Hume, H. H. Fla. Agri. Exp. Sta. Bull. 53: 164. 1900.
5. Gossard, H. A. Fla. Agri. Exp. Sta. Rept. 65. 1901.
6. Gossard, H. A. Fla. Agri. Exp. Sta. Bull. 67: 21-22. 1903.
7. Hume, H. H. Citrus Fruits and Their Culture, 550. 1904.
8. Sellards, E. H. Fla. Agri. Exp. Sta. Rept. 26. 1905.
9. Parkin, J. Fungi Parasitic upon Scale Insects, Annals Roy. Bot. Gard.
Peradeniya 3': 52. 19o6.
o1. Berger, E. W. Fla. Agri. Exp. Sta. Rept. xix. 19o6.
ii. Berger, i. W. Proc. Fla. Hort. Soc. 75, 79. 1907.
12. Berger, E. W. Fla. Agri. Exp. Sta. Bull. 88: 64-65. 1907.
I3. Berger, E. W. Fla. Agri. Exp. Sta. Rept. xxxi. 1907.
14. Rolfs, P. H., and Fawcett, H. S. Fla. Agri. Exp. Sta. Bull. 94: 17-19.
I5. Fawcett, H. S. Fungi Parasitic upon Aleyrodes Citri, Univ. Fla.
Special Stud. I: 34-36. I908.
UNIVERSITY OF FLORIDA,
EXPLANATION OF PLATES XXVIII AND XXIX
FIG. I. Sporodochia of Aegerita Webberi on upper side of an orange
leaf. X 1.
FIG. 2. Brown stromata of Aegerita Webberi on lower side of same leaf
indicating position of the whitefly larvae that have been parasitized. The
three pustules that show white in the figure are of Aschersonia Aleyrodis
Webber. X |.
FIG. 3. Two sporodochia of Aegerita Webberi germinated in 5 per cent.
glucose solution showing growth of mycelium. X 75.
FIG. 4. Portion of a mycelium in a hanging-drop culture more highly
magnified, showing the intercrossing of the hyphae. X 150.
FIG. 5. Sporodochia of Aegerita Webberi mounted in water showing
conidia-like cells and appendages. X 80.
FIG. 6. Same sporodochia broken up under a cover glass to show the
clusters and chains of cells. X 80.
FIG. 7. Larva of Aleyrodes Citri parasitized by inoculation with sporo-
dochia of Aegerita Webberi. Near the middle and toward one side, the
mycelium of the fungus may be seen very clearly.