310 
through the central pads, fig. 16D, and 
some beetles were found embedded there. 
Insect activity on mats was greatest 
during April, May, and June, when more 
species were found than in any other 
months. Very few fresh mats were found 
in July, and insects were seldom found on 
them. 
Few attempts were made to determine 
exact numbers of insects on mats. Mem- 
bers of the families Nitidulidae, Staphy- 
linidae, and Histeridae, and of the order 
Collembola, obviously were much more 
abundant than any of the others. Ap- 
proximately 75 to 100 adult Nitidulidae 
and as many larvae were commonly seen 
on a single mat. Members of the Staph- 
ylinidae and of the Collembola, which 
are much smaller than the Nitidulidae, 
were even more numerous. Adult insects 
were found most frequently on class III 
and class IV mats and larvae on class IV 
and class V mats, table 14. Insects were 
seldom present on immature mats, as the 
cracks in the bark over such mats usually 
were very narrow, barely perceptible 
openings that could admit only the small- 
est insects. Small individuals of the Niti- 
dulidae were often seen making unsuccess- 
ful attempts to squeeze through these 
openings. The fact that immature (class 
I) mats are not so strongly odoriferous as 
are mats of the mature and aging classes 
also may account for the presence of 
fewer insects on the younger mats. 
Other Agents Associated With Mats 
Agents other than insects may have 
been responsible for hastening the decline 
and deterioration of natural reservoirs of 
inoculum. Feeding by rodents on mycelial 
mats of Endoconidiophora fagacearum in 
Pennsylvania was reported by Morris & 
Fergus (1952). Squirrels caused consid- 
erable damage to mycelial mats in IIli- 
nois (Himelick et al. 1953) during the 
winter of 1952-53, and new damage of 
this kind, fig. 17, was seen in May and 
June of 1953. The rodents seemed to 
have been interested in only the central 
pads of young mats, but, to reach the 
pads, they had torn large holes in the 
bark, exposing the fungus to other de- 
structive elements, such as insects, wind, 
rain, and other fungi. 
ILLiNoIs NATURAL History SURVEY BULLETIN 
Vol. 26, Art. 3 
During the summer months, the mat- 
bearing trees were often exposed to the 
direct rays of the sun, and temperatures 
became very high under the bark. The 
temperatures for one tree at 3:00 p.m. 
on July 23, 1953, were 32.5 degrees out- 
side and 41.0 degrees under the bark on 
the sunny side of the trunk, as determined 
by actual thermometer readings. On the 
shaded side, the temperatures were 29.5 
degrees outside and 30.5 degrees beneath 
the bark. No further mat production oc- 
curred on this tree, and the fungus could 
not be isolated from the wood. During 
the winter months, mats were subjected 
to alternate freezing and thawing. At 
this time the mats often were continu- 
ously wet for several days and finally be- 
came slimy with bacteria and other micro- 
scopic forms of life. 
Many mycelial mats were found to be 
overrun by wood-rotting fungi, fig. 18, ex- 
cept for the central pad of each, which 
seemed to repel invasion of these fungi. 
However, the pads were readily attacked 
by other fungi. Graphium, in particular, 
throve well in aging pads, where it en- 
tangled the pad cells in a thick mass of 
hyphal strands and produced abundant 
coremia and slimy masses of spores. 
Other agents that were commonly asso- 
ciated with the mats of the oak wilt fun- 
gus but that were less destructive were 
mites, nematodes, and crustacea. Mites 
were usually abundant during all months 
on mats in all stages of decline. Nema- 
todes of the genus Diplogaster* were very 
abundant on old perithecium-bearing mats. 
They infested the masses of exuded asco- 
spores of Endoconidiophora fagacearum, 
in some cases hundreds in a single mass. 
These nematodes had oral openings that 
measured about 5.6 microns, large enough 
to admit conidia or ascospores of the oak 
wilt fungus. However, attempts to en- 
tice the nematodes to feed upon the spores 
of the fungus on the surface of agar were 
unsuccessful. Crustaceans of the species 
Porcellio rathkei were sometimes found on — 
mycelial mats that had developed on bark — 
pieces on the forest floor, but they were 
not observed feeding on the fungus of the 
oak wilt disease. d 
fins 
ol Br 1 Saas Bea 
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_ 
* Nematodes were identified by Dr..M. B. Linford, De- 
¢ 
partment of Horticulture, University of Illinois. " 
