If one of these essential amino-acids is
not present in the amount required by the bees, then the bees cannot fully
digest as protein all the protein they have eaten. For instance, if one
of the amino-acids is required at 4% and is only available at 3%, then
only three-quarters of the total protein consumed can be utilised by the
bees, as body-building protein.
Analysis of pollen protein has indicated that most
of these essential amino-acids are at satisfactory levels. However, Iso-leucine
and on a few occasions Valine are below these desired levels.
De Groot (1953) found that the amino-acid iso-leucine
is required by honey bees at 4% of the digested protein. Analysis of pollen
samples for this book found that iso-leucine contained in the pollen protein
was usually below this 4%, in a range of 2.7% to 4%. This observation was
recorded in Victorian eucalypts by Lynn Muss (Muss 1996), and also by Ryner
and Landridge (1985), and in Queensland pollens by Kleinschmidt (1984).
Studies carried out at Wollongbar N.S.W. on iso-leucine
(Stace and White 1994) found that a response to supplementary iso-leucine
can be observed when bees are breeding rapidly but have only limited amounts
of pollen. The supplementary iso-leucine allowed the bees to fully digest
as protein, all the protein in the pollen consumed.
This indicates that, when there is a protein deficiency
with bees foraging on Australian plants, it is most likely that the essential
amino-acid, iso-leucine is the major limiting factor.
The practical application of this information is
that bee feed supplements should have over 4% iso-leucine. This will allow
the feedstuff to be a true supplement, in that it supplies both additional
protein and additional iso-leucine. The additional iso-leucine allows for
a better utilisation of the field-collected pollen.
Bees store protein in their body, and use it to make
wings, muscles and other body organs. The higher the level of protein in
their bodies, the stronger the bees are and the longer they can live.
Bees can have a very high body-protein of over 60%
crude protein, at which time they are strong, long-lived bees, with the
ability to collect lots of honey. Or at the other extreme they can have
low body-protein of less than 30% (Kleinschmidt 1988). When bees have low
body-protein they will live only a short time, suffer from diseases like
European brood disease (EBD) and nosema, and be very poor honey producers.
High body-protein bees are essential in autumn, so
the bees can combat nosema, overwinter in strong condition, and have plenty
of body-protein to use for hive build-up in the spring. Bees with a low
body-protein in the autumn will generally not overwinter well, will be
susceptible to nosema and "spring dwindles" and possibly have restricted
breeding in the spring.
Bee body-protein is reduced by honey production,
cold or hot weather, wax production, and an increase in breeding, especially
during the spring build-up period.
Bee body-protein will increase if the bees are getting
plenty of pollen with more than 20% digestible crude protein, especially
if they are not stressed by heavy honey production and extremes in weather.
Bee body-protein is a good measure of the hives'
ability to survive winter, collect good honey crops, and overcome many
of the bee diseases, like European brood disease or chalk brood. The higher
the body-protein level, the better the bees will be able to collect economic
yields of honey, pollinate crops, and produce queen bees.
Protein and stress
Bees require protein at different rates, according
to the level of stress they are under.
By understanding the concept of bee stress, beekeepers
are able to make better management decisions about bee nutrition.
Low stress hives show little activity. The bees may
be breeding at a constant rate, there is little or no honey to gather,
the air temperature is warm (above 20oC) and their needs are small. Under
such conditions, bee hives will increase their body-protein, and maintain
or slowly increase their populations if they can collect pollen at 12%
to 15% crude protein. Under such conditions hives will develop to a reasonable
strength in six to eight weeks. This can be observed when bees are collecting
ground flora such as flatweed (false dandelion). During nutrition trials
at Wollongbar Agricultural Institute in 1993, hives foraging only on flatweed
increased their body-protein from 40% to 60% in six weeks. The hives did
not store honey or increase in size. However, the low stress allowed the
hives to develop high body-protein (Stace personal observation).
High stress situations
Honey bees in a high stress situation require surplus
pollen with a digestible crude protein level greater than 20%. The higher
the stress the greater their need for protein.
High stress in beehives occurs when:
. the bees are on a honey flow. The heavier the
honey flow the greater the stress.
. the bees are increasing their breeding rate or
brood area, as occurs in spring or during a high nectar stimulated breeding
program. (Stace 1994)
. it is too cool or too hot (below 20°C or
over 35°C) and the bees are working hard for their pollen and nectar
(eg. a white box winter honey flow, or lucerne in summer).
Examples of high stress are:
White box stress
White box, which flowers in the winter, is known
to be hard on bees. The crude protein of it's pollen is 17% to 20% and
the essential amino-acid iso-leucine is 3.7% to 3.8% of the crude protein.
This would give a digestible protein of 16% to 19%. This is below the desirable
20%. The bees are highly stressed because the temperature is low, the honey
flow is good, the wax production is high, and they are stimulated to breed.
Honey bees working white box often produce 20 to 40 kg of honey, then the
hive populations collapse, usually due to protein stress.
The crude protein of lucerne pollen is 20% to 24%
(table 2). This should be sufficient for the bees to maintain hive numbers
and body-protein, but this appears not to be the case. Beehives tend to
become weak and inactive when working lucerne only. The cause is a shortage
of one of the amino-acids (iso-leucine) that comprise the pollen protein.
Table 2: Protein and amino-acid ratios Lucerne