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 II

Mean fall conditions ( ± SE) of 408 honey bee colonies found alive or dead the following spring in Ontario, Canada, for different factors that could be associated to colony mortality and low spring and summer bee populations. P based on Mann-Whitney U tests.

Factor	Alive	Dead	P
Bee population¹	8.0 ± 0.1	5.9 ± 0.2	< 0.0001
Food reserves (kg)	25.4 ± 0.5	19.0 ± 0.9	< 0.0001
Varroa mite infestation²	2.9 ± 0.2	11.1 ± 1.5	< 0.0001
Tracheal mite infestation³	0.2 ± 0.1	3.1 ± 1.3	< 0.001
Nosema infection⁴	6734	18018	0.2847
	± 3238	± 14923

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.