GUT FUNGI OF INVERTEBRATES
Robert W. Lichtwardtur knowledge of tropical fungi is minimal.
Fungi associated with insects and other
arthropods are just beginning to be studied.
In Mont ever de, a cryptic but common group of fungi
exists whose species live within the digestive tract of
certain aquatic insects and other arthropods. These
Trichornycetes (Zygomycota) are among the most un-
usual and specialized fungi known (Lichtwardt 1986,
1997). Gut fungi may live predominantly as commen-
sals in the arthropod, with the fungus taking a neu-
tral role as it obtains its food from substances pass-
ing through the intestinal tract. Mosquito larvae, when
deprived of certain essential nutrients such as sterols
and B vitamins, can benefit from fungal biosynthesis
of those nutrients (Horn and Lichtwardt 1981), At the
other extreme, Smittium morbosum (Harpellales) is
lethal to mosquito larvae (Sweeney 1981), and certain
Harpellales invade the ovaries of developing adults,
forming fungal cysts that repress egg development
(Moss and Descals 1986, Lichtwardt 1996). Such
cysts are oviposited by the flying adult and serve as
a mechanism for fungal dissemination. As a result, gut
fungi may reduce populations of aquatic insects, in-
cluding pests and disease vectors such as mosquitoes
and blackflies.
Studies in Monteverde were carried out over four
periods from 1984 to 1991 as part of a larger investi-
gation of Costa Rican gut fungi. The emphasis in
Monteverde was on Harpellales in aquatic insect
larvae, mostly larval Simuliidae (blackflies) and
Chironomidae (midges). Collection sites were primar-
ily (a) flowing waters within the MCFP, including
Quebrada Cuecha and nearby streams; (b) Quebrada
Maquina; and (c) several stretches of the Rio Guacimal
west of the main road. The streams had a mean tem-
perature of 16.7°C (range = 15.5° -17.4°C), consider-
ably cooler than the lowland streams investigated at
La Selva (24.Q°-25.8°C; mean 24.4°C) and the lowland
portions of streams draining from the Cordilleras in
Guanacaste Province (22.5°-28.Q°C; mean 25.3°C).
Most trichomycete species reported here are un-
described and are known only from Costa Rica; only
their generic identity is given. Lichtwardt (1994) de-
scribed Trichornycetes inhabiting insects from tank
plants and other still-water habitats.
Simuliidae. Blackfly larvae attach to substrates in
fast-flowing waters of streams and rivers. In Monte-
verde, virtually all blackflies are infected with one or
more genera of Harpellales (Harpella, Genistellospora,
Pennella, or Smittium; Figs. 3.27, 3.28) and, more
rarely, Simuliomyces microsporus, Commonly, two or
three species of these fungal genera coinhabit the same
blackfly gut. Infected Simuliidae included Simulium
callidium, S. ochraceum, and S. metallicum group, and
possibly other species of blackfly larvae.
Species of Harpella attach to the midgufs peri-
trophic membrane. Nearly all blackflies were infected
with a new species of Harpella (Fig. 3.28A,B), in
Monteverde and in all other regions of Costa Rica
where blackflies were collected. H. melusinae lives
in most larval blackfly populations throughout much
of the Northern Hemisphere, as well as New Zealand
and Australia, but it has never been found in Costa
Rica. At least seven species of Harpellales known to
occur in Costa Rica have a widespread distribution
in temperate zones.
Species of Genistellospora and/or Pennella (Fig.
3.27A,B,C) were present in most blackfly hindguts,
even at the headwaters of small streams where larvae
were relatively few. Certain species of these fungal
genera were found only in Monteverde or other high-
altitude sites sampled in Costa Rica, in contrast to
other species of Genistellospora and Pennella, which
appear to infect blackflies only at lower altitudes. A
common but new species of Smittium was present in
Rio Guacimal in both blackfly and midge larvae, and
was one of several species of Smittium isolated in
culture.
Chironomidae. Midge larvae were relatively scarce
in unpolluted streams in Monteverde, though a num-
ber of larvae of Cricotopus sp. and Cardiocladius sp.
were collected in Quebrada Maquina. These were
infected with Smittium sp., a trichomycete (Harpel-
lales) that can infect both midges and blackflies. Midge
larvae (Lymnophyes sp., Metriocnemus sp.) were col-
lected from water in the leaf bases of several brome-
liads and a Xanthosoma plant, and some of the lar-
vae were infected with Smittium spp. (Lichtwardt
1994).
A remarkably dense insect fauna was found in Rio
Guacimal below an effluent that consisted mostly of
whey discharging through a plastic pipe from the
dairy plant (lecherfa) upstream (see Gill, "Impact of
Monteverde Lecheria," pp. 446-447). The polluted
stretch of Rio Guacimal contained abundant popula-
tions of the following midges: Chironomus sp., Crypto-
chironomus sp., Cardiocladius sp., Cricotopus sp.,
Polypedilum sp., and an unidentified genus of Ortho-83 Plants and VegetationO