Abstract
Varroa mites (V. destructor) are a major threat to honey bees (Apis melilfera) and beekeeping worldwide and likely lead to colony decline if colonies are not treated. Most treatments involve chemical control of the mites; however, Varroa has evolved resistance to many of these miticides, leaving beekeepers with a limited number of alternatives. A non-chemical control method is highly desirable for numerous reasons including lack of chemical residues and decreased likelihood of resistance. Varroa sensitive hygiene behavior is one of two behaviors identified that are most important for controlling the growth of Varroa populations in bee hives. To identify genes influencing this trait, a study was conducted to map quantitative trait loci (QTL). Individual workers of a backcross family were observed and evaluated for their VSH behavior in a mite-infested observation hive. Bees that uncapped or removed pupae were identified. The genotypes for 1,340 informative single nucleotide polymorphisms were used to construct a high-resolution genetic map and interval mapping was used to analyze the association of the genotypes with the performance of Varroa sensitive hygiene. We identified one major QTL on chromosome 9 (LOD score = 3.21) and a suggestive QTL on chromosome 1 (LOD = 1.95). The QTL confidence interval on chromosome 9 contains the gene ‘no receptor potential A’ and a dopamine receptor. ‘No receptor potential A’ is involved in vision and olfaction in Drosophila, and dopamine signaling has been previously shown to be required for aversive olfactory learning in honey bees, which is probably necessary for identifying mites within brood cells. Further studies on these candidate genes may allow for breeding bees with this trait using marker-assisted selection.
Highlights
Pollination by honey bees (Apis mellifera) is an important part of modern agriculture, and honey bee health has been receiving increased attention recently from the public, beekeepers, and researchers
The objective of the current study was to use quantitative trait loci (QTL) mapping on a genome-wide scale to look for segregating chromosomal regions for the Varroa sensitive hygiene (VSH) trait
Permutation tests indicated that this QTL is not significant with the genome-wide threshold for p,0.05, it is does surpass the chromosome-wide threshold for p,0.05 (1000 iterations and p,0.05 thresholds: genome-wide = 3.41, chromosome-wide = 2.04) and is above the widely used theoretical threshold of 3.0 [71,73,74,75]
Summary
Pollination by honey bees (Apis mellifera) is an important part of modern agriculture, and honey bee health has been receiving increased attention recently from the public, beekeepers, and researchers. Varroa parasitism of honey bees is widely considered to be the greatest threat to beekeeping and has led to substantial colony losses worldwide [4,5,6,7,8,9,10]. These obligate ectoparasites live in the nest of honey bees and harm individuals and colonies. When the adult bee emerges, mature female mites leave the worker cell and enter a phoretic stage while feeding on the hemolymph of adult bees [13]. Untreated Varroa-infested colonies usually die after one to four years of mite infestation; there have been reports of untreated hives with mites surviving for up to six years [3,21,22,23,24,25,26]
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