Gloria DeGrandi-Hoffman

Honey bee aggression supports a link between gene regulation and behavioral evolution

A prominent theory states that animal phenotypes arise by evolutionary changes in gene regulation, but the extent to which this theory holds true for behavioral evolution is not known. Because “nature and nurture” are now understood to involve hereditary and environmental influences on gene expression, we studied whether environmental influences on a behavioral phenotype, i.e., aggression, could have evolved into inherited differences via changes in gene expression. Here, with microarray analysis of honey bees, we show that aggression-related genes with inherited patterns of brain expression are also environmentally regulated. There were expression differences in the brain for hundreds of genes between the highly aggressive Africanized honey bee compared with European honey bee (EHB) subspecies. Similar results were obtained for EHB in response to exposure to alarm pheromone (which provokes aggression) and when comparing old and young bees (aggressive tendencies increase with age). There was significant overlap of the gene lists generated from these three microarray experiments. Moreover, there was statistical enrichment of several of the same cis regulatory motifs in promoters of genes on all three gene lists. Aggression shows a remarkably robust brain molecular signature regardless of whether it occurs because of inherited, age-related, or environmental (social) factors. It appears that one element in the evolution of different degrees of aggressive behavior in honey bees involved changes in regulation of genes that mediate the response to alarm pheromone.

The effect of diet on protein concentration, hypopharyngeal gland development and virus load in worker honey bees (Apis mellifera L.).

Elucidating the mechanisms by which honey bees process pollen vs. protein supplements are important in the generation of artificial diets needed to sustain managed honeybees. We measured the effects of diet on protein concentration, hypopharyngeal gland development and virus titers in worker honey bees fed either pollen, a protein supplement (MegaBee), or a protein-free diet of sugar syrup. Workers consumed more pollen than protein supplement, but protein amounts and size of hypopharyngeal gland acini did not differ between the two feeding treatments. Bees fed sugar syrup alone had lower protein concentrations and smaller hypopharyngeal glands compared with the other feeding treatments especially as the bees aged. Deformed wing virus was detected in workers at the start of a trial. The virus concentrations increased as bees aged and were highest in those fed sugar syrup and lowest in bees fed pollen. Overall results suggest a connection between diet, protein levels and immune response and indicate that colony losses might be reduced by alleviating protein stress through supplemental feeding.

An emerging paradigm of colony health: microbial balance of the honey bee and hive (Apis mellifera)

Across the globe, honey bee populations have been declining at an unprecedented rate. Managed honey bees are highly social, frequent a multitude of environmental niches, and continually share food, conditions that promote the transmission of parasites and pathogens. Additionally, commercial honey bees used in agriculture are stressed by crowding and frequent transport, and exposed to a plethora of agricultural chemicals and their associated byproducts. When considering this problem, the hive of the honey bee may be best characterized as an extended organism that not only houses developing young and nutrient rich food stores, but also serves as a niche for symbiotic microbial communities that aid in nutrition and defend against pathogens. The niche requirements and maintenance of beneficial honey bee symbionts are largely unknown, as are the ways in which such communities contribute to honey bee nutrition, immunity, and overall health. In this review, we argue that the honey bee should be viewed as a model system to examine the effect of microbial communities on host nutrition and pathogen defense. A systems view focused on the interaction of the honey bee with its associated microbial community is needed to understand the growing agricultural challenges faced by this economically important organism. The road to sustainable honey bee pollination may eventually require the detoxification of agricultural systems, and in the short term, the integrated management of honey bee microbial systems.

Israeli acute paralysis virus: epidemiology, pathogenesis and implications for honey bee health

Israeli acute paralysis virus (IAPV) is a widespread RNA virus of honey bees that has been linked with colony losses. Here we describe the transmission, prevalence, and genetic traits of this virus, along with host transcriptional responses to infections. Further, we present RNAi-based strategies for limiting an important mechanism used by IAPV to subvert host defenses. Our study shows that IAPV is established as a persistent infection in honey bee populations, likely enabled by both horizontal and vertical transmission pathways. The phenotypic differences in pathology among different strains of IAPV found globally may be due to high levels of standing genetic variation. Microarray profiles of host responses to IAPV infection revealed that mitochondrial function is the most significantly affected biological process, suggesting that viral infection causes significant disturbance in energy-related host processes. The expression of genes involved in immune pathways in adult bees indicates that IAPV infection triggers active immune responses. The evidence that silencing an IAPV-encoded putative suppressor of RNAi reduces IAPV replication suggests a functional assignment for a particular genomic region of IAPV and closely related viruses from the Family Dicistroviridae, and indicates a novel therapeutic strategy for limiting multiple honey bee viruses simultaneously and reducing colony losses due to viral diseases. We believe that the knowledge and insights gained from this study will provide a new platform for continuing studies of the IAPV–host interactions and have positive implications for disease management that will lead to mitigation of escalating honey bee colony losses worldwide.

Comparisons of pollen substitute diets for honey bees : consumption rates by colonies and effects on brood and adult populations

Summary Commercially available pollen substitute diets for honey bees (Apis mellifera L.) were evaluated for consumption and colony growth (brood and adult populations) and compared with pollen cake and high fructose corn syrup (HFCS). Two trials were conducted; the first for 3 months during the fall and winter and a second for 2 months in the summer. Three diets were tested in Trial 1 (Diet-1, Diet-2, and Diet-3 (liquid and patty form)) and Diet-2 and Diet-3 (patty) in Trial 2. In both Trials, Diet-2 and Diet-3 patty were consumed at rates that were comparable to pollen cake. Colonies consumed significantly less Diet-1 than the other diets. There was a significant relationship between the amount of diet consumed and the change in brood area and adult population size in both Trials. Colonies fed Diet-3 patty produced significantly more brood than those fed pollen cake or any other diet in Trial 1. The lowest brood production occurred in colonies fed Diet-1 or HFCS. Adult populations in colonies fed Diet-3 liquid or patty did not differ from those fed pollen cake, and were significantly larger than colonies fed Diet-1 or Diet-2. In Trial 1, when some pollen was being collected by colonies, Diet-2 and Diet-3 did not differ from pollen cake in brood or adult population growth.

Dynamics of Persistent and Acute Deformed Wing Virus Infections in Honey Bees, Apis mellifera

The dynamics of viruses are critical to our understanding of disease pathogenesis. Using honey bee Deformed wing virus (DWV) as a model, we conducted field and laboratory studies to investigate the roles of abiotic and biotic stress factors as well as host health conditions in dynamics of virus replication in honey bees. The results showed that temperature decline could lead to not only significant decrease in the rate for pupae to emerge as adult bees, but also an increased severity of the virus infection in emerged bees, partly explaining the high levels of winter losses of managed honey bees, Apis mellifera, around the world. By experimentally exposing adult bees with variable levels of parasitic mite Varroa destructor, we showed that the severity of DWV infection was positively correlated with the density and time period of Varroa mite infestation, confirming the role of Varroa mites in virus transmission and activation in honey bees. Further, we showed that host conditions have a significant impact on the outcome of DWV infection as bees that originate from strong colonies resist DWV infection and replication significantly better than bee originating from weak colonies. The information obtained from this study has important implications for enhancing our understanding of host‑pathogen interactions and can be used to develop effective disease control strategies for honey bees.

Effects of Honey Bee (Hymenoptera: Apidae) Foraging on Seed Set in Self-fertile Sunflowers (Helianthus annuus L)

Abstract Ten self-fertile commercial sunflowers cultivars were evaluated for seed set with and without exposure to bees. In the first planting, the number of foraging honey bees was smaller than in the second, and seed set for most cultivars did not differ between those bagged to exclude bees and ones that were open pollinated. In the second planting, however, a majority of cultivars had significantly greater seed set when capitula were exposed to bees compared with when they were not. The weight of seeds from open-pollinated capitula was greater than from those where bees were excluded. Environmental conditions also played a role in seed set as evidenced by differences between plantings in set on bagged capitula. In the first planting, average maximum and minimum temperatures were significantly higher than in the second, and overall seed set was significantly lower in capitula where bees were excluded compared with the second planting. Under the high temperature conditions, however, some cultivars set four times more seed on open-pollinated capitula compared with those that were bagged. These results suggest that foraging activity and cross-pollination by bees might mitigate reductions in seed set caused by high temperatures.

The flow of incoming nectar through a honey bee (Apis mellifera L.) colony as revealed by a protein marker.

Summary: The flow of incoming nectar in honeybee (Apis mellifera L.) colonies was simulated by feeding a sucrose solution labeled with a novel protein (rabbit IgG) marker and then analyzing bee and colony samples using an enzyme-linked immunosorbant assay (ELISA). The labeled sucrose solution was quickly transported to food storage and brood combs. Within 2h, equal percentages of worker bees from food storage combs, nurse bees and nectar samples tested positive for the marker. Percentages of nurse bees and larvae testing positive also were equal within the first 2 h of feeding it to a colony and these percentages increased over time. Our results suggest that workers with nectar loads deposit them into cells on either food storage or brood comb with equal frequency. The labeled sucrose solution transported to the brood comb is subsequently used by nurse bees to feed larvae. How the deposition of incoming nectar in brood comb might possibly integrate the activities of foragers and nurse bees is discussed.

Nutrition, immunity and viral infections in honey bees

Viruses and other pathogens can spread rapidly in social insect colonies from close contacts among nestmates, food sharing and periods of confinement. Here we discuss how honey bees decrease the risk of disease outbreaks by a combination of behaviors (social immunity) and individual immune function. There is a relationship between the effectiveness of social and individual immunity and the nutritional state of the colony. Parasitic Varroa mites undermine the relationship because they reduce nutrient levels, suppress individual immune function and transmit viruses. Future research directions to better understand the dynamics of the nutrition-immunity relationship based on levels of stress, time of year and colony demographics are discussed.

New meta-analysis tools reveal common transcriptional regulatory basis for multiple determinants of behavior

A fundamental problem in meta-analysis is how to systematically combine information from multiple statistical tests to rigorously evaluate a single overarching hypothesis. This problem occurs in systems biology when attempting to map genomic attributes to complex phenotypes such as behavior. Behavior and other complex phenotypes are influenced by intrinsic and environmental determinants that act on the transcriptome, but little is known about how these determinants interact at the molecular level. We developed an informatic technique that identifies statistically significant meta-associations between gene expression patterns and transcription factor combinations. Deploying this technique for brain transcriptome profiles from ca. 400 individual bees, we show that diverse determinants of behavior rely on shared combinations of transcription factors. These relationships were revealed only when we considered complex and variable regulatory rules, suggesting that these shared transcription factors are used in distinct ways by different determinants. This regulatory code would have been missed by traditional gene coexpression or cis-regulatory analytic methods. We expect that our meta-analysis tools will be useful for a broad array of problems in systems biology and other fields.