An article in The Herald [1] was headlined "Moths
may hold the key to cutting in lab tests on mammals". It was one of many
articles in the past weeks about the use of wax moth larvae (Galleria mellonella) in toxicity and
antibiotic testing, reducing dependence on laboratory mammals such as mice and
rats. This is not a new approach and the use of these moth larvae in laboratory
testing has been reviewed by Desbois and Coote [2]. The lack of a standardised
source of larvae has been a hindrance in testing as, without a consistent
supply of known strains, there is likely to be variability in test results
caused by variations in the stock used. This problem has been overcome by
Biosystems Technology [3], a company that provides wax moth larvae as a standardised
product under the name TruLarv.
It is understandable that the articles
in the media focussed on the reduction of the need for testing on mammals, but
none of those I read discussed the biology of the moths, their association with
honey bees, and the possible evolution of the relationship. For bee-keepers,
wax moths (above, upper) can be a problem as their larvae attack honeycombs
(above, lower from [4]), while being protected by the silk that they produce. In
addition to Galleria mellonella, the
most important wax moth for apiarists, another species Achroia grisella is also found and the two have slightly different
life cycles in temperate countries: G.
mellonella overwintering as mature larvae or pupae in silk cocoons and A. grisella in the egg or larval stages
[5].
The association of wax moths with
hives of bees is of long standing and was known to Aristotle [6], bee-keeping
having been a well-established practice for millennia. Larvae, the only
feeding stage of the insect, eat wax and any material that is in close contact with it. They
do not destroy nests of bees, but cause a decrease in the efficiency of raising
brood and they reduce the output of honey from hives - the silk and faecal
material produced by larvae also make an unsightly mess in the honeycomb. Having hives arranged in
close proximity, as may be the preference of a bee-keeper, results in an increased
likelihood of the spread of wax moths once they have entered one of the hives,
a problem familiar to those who investigate pests in monocultures.
The natural history of wax moths is
as interesting, if not more interesting, than the use of the larvae as test organisms.
It is also fascinating to speculate on how the original association between wax
moths and bees came about. Ancestrally, the moths colonised the nest of wild
bees, but it is not known when this occurred and it presumably resulted from a sudden
shift from feeding on vegetation or animal by-products, the typical diets of
moth larvae. The biting mouthparts of larvae were certainly pre-adapted for feeding on
honeycombs and the use of silk, common in larval moths, gave some protection from
possible attack by the bees. But how did they first invade bee nests and what
steps then evolved to allow the more specific association between bee moths and
honeybees? This can only be speculated upon and it is interesting that it
occurred in two closely-related taxa, G.
mellonella and A. grisella. Perhaps
speciation of the moths occurred after the evolution of the wax-feeding habit -
or is this a case of adaptations evolving in parallel, way before humans came
on the scene?
[2] A.P.Desbois and P.J.Coote
(2012) Utility of Greater Wax Moth larva (Galleria mellonella) for evaluating
the toxicity and efficacy of new antibacterial agents. Advances in Applied Microbiology 78:25-53.
[4] A.J.Cook (1880) Manual of the
Apiary. Chicago, Thomas G. Newman.
[6] Warren Whitcomb Jr. (1936)
The Wax Moth and its control. United
States Department of Agriculture Circular no. 386.
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