Safekeeping Fungi That
Richard Humber, microbiologist
and insect mycologist, checks
for a requested fungal isolate
in one of the several crowded
nitrogen tanks holding the
ARSEF culture collection.
The collection comprises
6,500 isolates from every
continent around the world.
Insect mycologist Richard Humber slowly lifts the thick
lid off the top of a round liquid-nitrogen tank used for super-cold
Once the fog that forms when the tank's air mixes with that of the humid laboratory clears, he gazes down at the tops of the elongated plastic tubes he keeps inside. He smiles.
"These are a bunch of little jewels," he says. "We hold
them very dear."
The jewels Humber speaks of aren't gemstones. They're specimens of
fungi that have potential to protect plants from insects, arthropods,
and nematodes. "The emphasis here," he says, "is on acquiring
and distributing strains for use as possible biological control agents."
Humber is curator of the ARS Collection of Entomopathogenic Fungal Cultures (ARSEF). It is the world's largest and most taxonomically diverse germplasm repository for fungi that attack insects, mites, spiders, nematodes, and other invertebrates.
It comprises nearly 6,500 isolates from more than 425 fungal species from every continent. And that's not counting several hundred stored samples not yet officially added to the collection. "This is a truly unique resource," he says.
Technician Karen Hansen packs
one of the hundreds of fungal
cultures shipped annually to
ARSEF clients throughout the
United States and around the
| ARSEF, which is on Cornell University's
campus at Ithaca, New York, helps ARS' Plant Protection Research Unit
fulfill its mission: To develop innovative methods to protect crops from
"We have fungi from 1,400 different locations, from 1,000 different
hosts," says Humber. "This represents an extremely high proportion
of all fungal species known to affect insects."
Over the past decade, ARSEF has emerged as a major resource in the search for fungal compounds to help replace pesticides, many of which have been phased out because of environmental concerns.
How the Collection Grew
Humber became the collection's curator in 1976, when it was part of the ARS Plant, Soil, and Water Laboratory at the University of Maine at Orono. At the time, it held fewer than 100 cultures.
He oversaw its moving twicefirst to Cornell to be a housed within the renowned Boyce Thompson Institute's Insect Pathology Program, and again in 1985, when it went across the street to the ARS Plant, Soil, and Nutrition Laboratory's building, where facilities had been remodeled to accommodate it.
Microbiologist and insect
mycologist Richard Humber
checks a specimen of a
before examining it by
both stereo and compound
microscopes to determine
the correct identification
of the fungus.
Most of the specimens are kept inside three liquid-nitrogen tanks. The shiny metal cylinders3 feet in diameter, 4 feet tallrepresent the latest technology for storing fungi cryogenically.
Inside each tank, grids of more than 1,500 aluminum canes, each a foot
long, stand vertically. They are completely immersed in liquid nitrogen
that chills them to 196° C. Each cane holds up to six vials,
which are guarded against the formation of lethal ice crystals by a
More Than Just a Repository
ARSEF is a complex facility equipped to examine and isolate specimens and to identify and distribute them. Shipping, receiving, and catalogingin addition to researchare part of a day's work as the staff makes the collection widely available to scientific, agricultural, and business communities.
"We strive to provide users with pure and accurately identified fungal cultures," says Humber. "In addition, we have always made identification services for specimens and cultures available free of charge to laboratories requesting them."
Technician Karen Hansen
examines a freeze-dried
culture of Beauveria bassiana
ready to be deposited into
the ARSEF collection.
| The collection is managed with
a customized computer program that tracks the names and origins of fungi,
host information, distribution requests, and shipping documents. "It
represents a giant leap from the card-catalog system we used to use,"
ARSEF has cultivated collaborations with more than 80 nations and enjoys
close relationships with scientists from Brazil, Denmark, Colombia,
South Africa, South Korea, China, and Russia.
On a recent visit to ARSEF, collaborators from Russia brought along
a book. "I immediately asked them if I could copy it," says
Humber. Within those pages were descriptions and diagrams about fungi
from regions not represented in the collection. "Although the text
was in Russian, the book had a lot of data on unrepresented areas, such
as eastern Siberia and southeastern Russia. It was a great addition
to our database."
"The visit was a great example of what we do with other collaborators,"
Humber says. "We pool data to get a complete understanding of the
items we access."
Supplying collaborators worldwide with isolates of fungi presents unique
challenges. "We are always having to think about what the fungi
will encounter from the time they leave here until the recipient gets
them," says Humber.
"We know that we want to speed shipments along if they have to
go where the temperature during transit might literally cook the fungi.
Also, we don't want anything left out on a shipping dock or runway in
a blinding snowstorm, although the fungi can usually tolerate cold better
Special steps are taken. First, regulatory permits are obtained. For
shipment, petri plates are doubly sealed with Parafilm, a stretchable
wrap that molds to the plate rims. They are then enclosed in zip-type
bags, and placed in bubble wrap. All wrapped plates are fitted snugly
into boxes with plenty of extra padding to make sure the cultures can
withstand routine shocks and bumps during handling and transit.
For cultures grown in liquid media in tissue culture flasks, the flask
caps are securely tightened and doubly sealed with film. Then the flasks
are bagged and padded for shipment. Sometimes liquid cultures are moved
into smaller containers to minimize shipment damage to delicate fungi
Since most ARSEF cultures are in the public domain, corporations have requested and used them in research encompassing agricultural, veterinary, and pharmaceutical applications. In addition, ARSEF absorbs collections from throughout the world that have been abandoned or are threatened for financial or political reasons.
The Rare and the Valuable
The lab has its rare specimens. Among these are the only known collected
samples of Neozygites tanajoae, a significant pathogen of cassava
green mites in South America. Cassava is a staple crop for poor farmers
thereand in Africawho cannot afford to apply pesticides
against the mite.
But it is the common fungi that are most valuable. "The reality
is that the agents that are most depended on are the lowest common denominatorsones
that have the widest host range and are easiest to grow, formulate,
and apply," says Humber. Within this group are Beauveria bassiana
and Metarhizium anisopliae.
B. bassiana is probably the most important fungus in the ARSEF
collection. Strains of it have infected nearly every insect pest against
which it has been tested. Also, it is the one species most frequently
used worldwide in applied, fungus-based, biocontrol programs. The fungus
has been requested countless times, and the collection maintains nearly
1,000 accessions of it, sampled from a wide range of hosts and locations.
M. anisopliae is the world's second most commonly encountered
and second most widely used insect fungus. It, too, affects a huge number
and diversity of insect hosts. It is used routinely in Brazil to control
spittlebugs on alfalfa or sugarcane, and one variety is now being applied
widely in Africa against locusts and grasshoppers.
Commercial products based on this fungal species were developed in
the United States with ARSEF participation for use against cockroaches
and termites. Several labs in the United States and Canada are exploring
its use against Formosan subterranean termites.
Unfortunately, the ARSEF laboratory that stores such tiny items is
running out of space. "We have to make room in the collection,
since there is a never-ending need for secure, long-term storage of
even more fungi for every conceivable purposeand even for uses
not yet imagined," says Humber.
In the meantime, Humber and his staff will have to continue applying
innovative techniques to store their precious "jewels" and
send them around the world to save crops from pests.By Luis
Pons, Agricultural Research Service Information Staff.
This research is part of Crop Protection and Quarantine, an ARS
National Program (#304) described on the World Wide Web at www.nps.ars.usda.gov.
"Safekeeping Fungi That Protect Plants Against Pests" was published in the April 2003 issue of Agricultural Research magazine.