Varroa destructor is the main culprit for the death and reduced populations of overwintered honey bee (Apis mellifera) colonies in Ontario, Canada

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Table I

Mean fall, spring, and summer conditions ( ± SE) of honey bee colonies in Ontario, Canada, for factors that could be associated to colony mortality and low spring and summer bee populations.

Factor	Fall⁵	Spring⁵	Summer⁵
Bee population¹	7.4 ± 0.1	4.3 ± 0.2	15.8 ± 0.5
Food reserves (kg)	23.6 ± 0.4	12.5 ± 0.5	42.6 ± 2.5
Varroa mite infestation²	5.1 ± 0.5	3.1 ± 0.6	1.5 ± 0.2
Tracheal mite infestation³	1.0 ± 0.4	0.8 ± 0.2	1.1 ± 0.4
Nosema infection⁴	9804	3108199	1142000
	± 4688	± 327722	± 118200

Number of frames covered by bees per hive;

number of mites per 100 bees;

number of parasitized bees in 100;

⁴

number of spores per bee.

⁵

N = 408, 297, and 278 for fall, spring, and summer, respectively.