both as minimum % w/w TP and as OB g^1
dry powder or OB ml^1 for liquid formula-
tions, or OB equivalents for formulated
products containing synergists or enhancing
factors. The % of inert ingredients should
also be specified. For liquid formulations,
viscosity at a specified temperature is nor-
mally included in the specifications. The par-
ticle size is also important and either a
particle-size spectrum or the results of other
particle-size estimations, such as a wet sieve
test, should be included. Most importantly,
specifications should include recommended
storage conditions and estimated shelf-life,
at both an ambient temperature, e.g. 20°C,
and under recommended storage conditions.
StorageThe shelf-life of BV products has been a sig-
nificant problem for consumer acceptance. It
has been proposed that 18 months is a mini-
mum target shelf-life for BV products
(Ignoffo and Couch, 1981). However, most
products currently available need to be
either refrigerated, deep-frozen, dried or
lyophilized to achieve shelf-lives comparable
to those of chemical products. In the OB of
BV, the infective virions are encased within a
protein crystal matrix that protects the virus.
Under the right conditions, BV can remain
active for many years. Some factors, such as
ultraviolet (UV) light, are well known to
cause the inactivation of BV even in suspen-
sion (Ignoffo and Garcia, 1992) and appropri-
ate UV-opaque packaging should be used to
prevent this. The OB is also pH-sensitive
and, while very stable between pH 4.0 and
9.0, activity is reported to deteriorate outside
this range (Ignoffo and Garcia, 1966). Thus,
products need to be checked for pH and
buffered if necessary. Where formulations
are prepared as dried powders, then the use
of moisture-excluding packaging is impor-
tant as BV powders are often hygroscopic
and the absorption of water can seriously
reduce BV viability.
The metabolic activity of microbial conta-
minants in unpurified NPV products can also
deter potential users through the production
of pungent and very unpleasant odours asso-
ciated with bacterial fermentation. This needs
to be controlled both through more effective
clean-up of harvested NPV and through
maintenance of effective handling and stor-
age conditions throughout the supply chain,
from production to end-user.Recommended minimum quality control for
BVDNA restriction profiles- Characterization of the isolate, using at
least three commonly used restriction
enzymes, e.g. EcoR1, HindIII, Pst1, BamH1
OB microscope counts (NPV)- On the technical product (after processing
prior to final formulation) or on formu-
lated product (this may not be practicable
with some powder formulations due to
presence of carrier).
Total bacterial count- Dilution plating on generalist agar media
for formulated product. Ideally, viable
counts should normally not exceed 1 × 108
cfu ml^1 for formulated products with an
activity of 1 × 109 OB ml^1 or 5 × 108 cfu
g^1 for formulated dry products.
Virulence (pathogenicity)- Standardized bioassay (median lethal
dose (LD 50 or LC 50 ) on final product,
using defined instar of a laboratory-
reared strain of the target pest. Results
should confirm that the potency ratio is
within defined limits specified for the
product and determined during product
development or 0.5 of a standard virus
preparation.
Conclusions
Quality control criteria are similar for fungi
and viruses in that products composed of
either organism must be safe, virulent to the
target pest, uncontaminated with humanQuality Control of Fungal and Viral Biocontrol Agents 259