The use of field-collected insects does have
significant potential drawbacks. It can be diffi-
cult for untrained collectors to distinguish lar-
vae of susceptible and non-susceptible species.
Larvae from the field can be carrying
pathogens that may compete with the selected
BV and reduce the yield of BV. Further,
microsporidia and Bacillusspp. can be difficult
to distinguish from NPV occlusion bodies
(OB) unless staff are well trained. However,
with proper procedures, the use of field-col-
lected larvae can still be a viable option for
cost-effective mass production of BV for some
species of insect host (Moscardi, 1999).
Production process and record keepingThe production process for BV is essentially
simple as the virus reproduces itself readily
and efficiently if ingested by a susceptible
host. Ensuring that this host has appropriate
conditions of temperature and humidity, with
an adequate food supply, is all that is required
to achieve virus propagation. However, full
and adequate records of all quality control
data need to be kept and reviewed regularly.
There is a tendency for staff involved in any
day-to-day production to become accustomed
to a routine and not to notice when small sys-
tematic deviations from norms occur. These
may be crucial signs that a problem is build-
ing up and it is important that these are inves-
tigated early. Records should be scrutinized
regularly by a separate reviewer who is not
involved directly in day-to-day production.
Host contaminationBy creating a favourable environment for BV
multiplication, the production system is vul-
nerable to contamination by unwanted ento-
mopathogens. Especially problematic are
chronic pathogens, such as some GV,
microsporidia and cypoviruses (CPV), whose
initial occurrence may cause little obvious
problem but whose uncontrolled spread can
significantly reduce BV production. Fungi
that colonize unused diet or faeces may also
become a problem, but this can usually be
controlled with effective hygiene and the use
of fungicide in the diet (Singh, 1977).
NutritionFor choice of food the options lie between an
artificial diet, usually an agar-based formula,
or fresh plant material. The latter is cheap
and can provide a balanced diet for species
of insects that are nutritionally demanding.
However, fresh material has drawbacks in
that nutritional quality may vary according
to season or growth stage and field-har-
vested material may be contaminated with
unwanted entomopathogens. For this reason,
specially grown plant material is preferable
and systems for growing sprouting
seedlings, such as wheat or barley, can
ensure a regular controllable supply for
species that require artificial diet to be sup-
plemented by fresh plant material.
However, most NPV production uses
agar-based artificial diets (Singh, 1977). Not
only do these ensure that nutritional quality
is controlled, but also the cooking or auto-
claving stages in diet preparation sterilize
the diet effectively to prevent unwanted
infection. Diets are usually made in batches
and cold-stored for a time prior to use; this
should be systematically monitored and
batches of diet should be disposed of as they
reach expiry (c. 7 days). Records of ingredi-
ents and supplies should also be kept so that
any problems can be checked back to deter-
mine if faulty ingredients are to blame. All
ingredients should be stored properly – in
refrigerators or freezers, as appropriate – and
batches replaced at predetermined intervals.
Cereal-based diet ingredients should be pur-
chased in bulk and subsamples tested before
use on insects (e.g. a suitable storage species)
to check for the presence of insecticide
residues, or they should be obtained from an
organic supplier.
The objective in mass insect rearing is to
produce large numbers of larvae of pre-
dictable size for virus infection continuously
in a controlled manner. This requires precise
control of the conditions in which eggs are
incubated and larvae reared. Therefore, con-
ditions (temperature, light cycles and
humidity) should be closely monitored and
clear records kept and regularly checked.
Records of production parameters, such as
insect weights at infection and harvesting,256 N.E. Jenkins and D. Grzywacz