Sr. Sanchezpena et Hg. Thorvilson, EFFECT OF LONG-TERM CRYOGENIC STORAGE AND CONIDIAL SUSPENDING AGENTS ON THE VIRULENCE OF BEAUVERIA-BASSIANA TOWARD SOLENOPSIS-INVICTA, Journal of invertebrate pathology, 65(3), 1995, pp. 248-252
Storage in liquid nitrogen has become a widespread tool in collections
of microbial germplasm. However, little information on the effects of
cryogenic storage on the virulence of entomopathogenic fungal strains
is available. In this work we compared the virulence of two subcultur
es of a Beauveria bassiana strain, one of which was maintained for 4 y
ears in liquid nitrogen and the other which was maintained under stand
ard laboratory conditions, passed through susceptible hosts (harvester
ants, Pogonomyrmex barbatus) and artificial media. Concurrently, we e
valuated the effects on virulence of three methods used to obtain B. b
assiana conidia in aqueous suspensions (centrifugation, sonication, or
the detergent Tween 80). Adult workers of the red imported fire ant,
Solenopsis invicta Buren (EIS menoptera: Formicidae), were used for bi
oassays. We compared treatments consisting of combinations of maintena
nce conditions and conidial suspension methods. Each treatment was tes
ted at two conidial concentrations (5 x 10(7) and 5 x 10(7) conidia/ml
). Ants were shaken in conidial suspensions and incubated in moist cha
mbers. Mortality among ants at Day 6 postinoculation was used for data
analysis. Strain maintenance conditions (storage in liquid nitrogen o
r maintenance under standard laboratory conditions) did not have an ef
fect on mortality levels of S. invicta workers nor did conidial suspen
sion treatments have a significant effect on mortality. Percentage mor
tality was mainly dependent upon the conidial concentration used and r
anged from 70.7 to 94.2% (mean values) for the high concentration and
from 24.0 to 72.5% for the low concentration. Storage in liquid nitrog
en (-196 degrees C) did not significantly modify the virulence of this
B. bassiana strain, compared to that of the same strain maintained me
tabolically active in a thermal window of 4-25 degrees C on live hosts
and artificial media. (C) 1995 Academic Press, Inc.