ABSTRACT
Commercial honey bee (Apis mellifera L.) colonies significantly contribute to agricultural productivity through crop pollination. Almond production requires the most colonies because there are more than a million acres of orchards that require cross-pollination for nut set. With the rising costs of managing and transporting colonies to almond orchards combined with the high colony losses beekeepers routinely experience, we asked if renting colonies for almond pollination was profitable. We conducted a longitudinal study on 190 colonies from their establishment in April until they were placed in almond orchards 10 mo later. In the fall, equal numbers of colonies were placed either in cold storage (CS) facilities or in outdoor apiaries for the winter. We found that the cost of overwintering colonies in CS was lower than in apiaries, but CS did not reduce overwintering losses. A key finding from our study is that there is little or no profit in renting colonies for almond pollination once summer management and overwintering costs are considered. Our only profitable venture was honey production in the summer. We propose alternative management strategies to lower costs and make almond pollination profitable. We also developed a decision tool for selecting colonies to overwinter in CS and reduce expenditures on those that will not reach sufficient size for almond pollination. Our study exposes the unsustainable financial burden experienced by migratory beekeepers that is not included in estimates of yearly colony losses, and underscores the urgent need for forage plantings to generate revenue from honey and improve overwinter survival.
Subject(s)
Honey , Hymenoptera , Prunus dulcis , Animals , Bees , Longitudinal Studies , PollinationABSTRACT
Free-ranging herbivores have yearly life cycles that generate dynamic resource needs. Honey bee colonies also have a yearly life cycle that might generate nutritional requirements that differ between times of brood rearing and colony expansion in the spring and population contraction and preparation for overwintering in the fall. To test this, we analyzed polyfloral mixes of spring and fall pollens to determine if the nutrient composition differed with season. Next, we fed both types of seasonal pollens to bees reared in spring and fall. We compared the development of brood food glands (i.e., hypopharyngeal glands - HPG), and the expression of genes in the fat body between bees fed pollen from the same (in-season) or different season (out-of-season) when they were reared. Because pathogen challenges often heighten the effects of nutritional stress, we infected a subset of bees with Nosema to determine if bees responded differently to the infection depending on the seasonal pollen they consumed. We found that spring and fall pollens were similar in total protein and lipid concentrations, but spring pollens had higher concentrations of amino and fatty acids that support HPG growth and brood production. Bees responded differently when fed in vs. out of season pollen. The HPG of both uninfected and Nosema-infected spring bees were larger when they were fed spring (in-season) compared to fall pollen. Spring bees differentially regulated more than 200 genes when fed in- vs. out-of-season pollen. When infected with Nosema, approximately 400 genes showed different infection-induced expression patterns in spring bees depending on pollen type. In contrast, HPG size in fall bees was not affected by pollen type, though HPG were smaller in those infected with Nosema. Very few genes were differentially expressed with pollen type in uninfected (4 genes) and infected fall bees (5 genes). Pollen type did not affect patterns of infection-induced expression in fall bees. Our data suggest that physiological responses to seasonal pollens differ between bees reared in the spring and fall with spring bees being significantly more sensitive to pollen type especially when infected with Nosema. This study provides evidence that seasonal pollens may provide levels of nutrients that align with the activities of honey bees during their yearly colony cycle. The findings are important for the planning and establishment of forage plantings to sustain honey bees, and in the development of seasonal nutritional supplements fed to colonies when pollen is unavailable.
