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25
To compare the degree of toxicity of the different moulds series
of experiments under like conditions, number of bees (taken from
the same hive in all instances), quantity of fungous material fed
etc. were started on July 23. The results are given in the above.
0.ı gram of Penicillium conditaneum given in 10 c.c. honey to 12
bees killed the bees within 4 days. Next in toxicity comes Mucor
Mucedo, which, the quantity being identical, killed the same number
of bees in 5 days, Penicillium sp., Penicillium stoloniferum and
Cladosporium herbarum seem to have about the same degree of
toxicity to bees, and were all inferior in virulence to Penicillium
conditaneum and Mucor.
The question of the difference in toxicity in different species of
moulds is very interesting. Species will likely be found which are
far more toxic to bees than those recorded in the above. The vi-
rulence of Penicillium puberulum, investigated by Atspere and Brack
(1) and discussed more in detail below, is slight compared with
toxic extracts obtained from species investigated by Srunr: (23) and
others. Even different strains of the same fungus have been shown
to possess different degrees of toxicity. Penicillium stoloniferum
probably includes several »physiological varielies» some of which
are toxic and some nontoxic (ALspere and Brack 1). Orro (20)
found the Italian strain of Aspergillus fumigatus, more toxic than
the German, and the American strain of this fungus investigated
by Turesson (24) was likewise found to be superior in virulence to
the German. The climate has undoubtedly something to do with
the different degrees of virulence in the moulds, those of warmer
climates being far more toxic than those of temperate climates.
This would also explain why bee-paralysis is much more prevalent
and virulent in warm than in cold climates.
Controls.
During the time the feeding experiments were run control cages
were used in every series. Four such series corresponding to the
series of feeding experiment with the different fungi were set up,
namely from June 27—July 3; July 12—17; July 17—23; July
23— 30.
Series I.
June 27. 15 bees were caged (taken from the same hive
as those used in the experiments with Penicillium sp. and Peni-
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