Zachary Y. Huang

Regulation of honey bee division of labor by colony age demography

Abstract The age at which worker honey bees begin foraging varies under different colony conditions. Previous studies have shown that juvenile hormone (JH) mediates this behavioral plasticity, and that worker-worker interactions influence both JH titers and age at first foraging. These results also indicated that the age at first foraging is delayed in the presence of foragers, suggesting that colony age demography directly influences temporal division of labor. We tested this hypothesis by determining whether behavioral or physiological development can be accelerated, delayed, or reversed by altering colony age structure. In three out of three trials, earlier onset of foraging was induced in colonies depleted of foragers compared to colonies depleted of an equal number of bees across all age classes. In two out of three trials, delayed onset of foraging was induced in colonies in which foragers were confined compared to colonies with free-flying foragers. Finally, in three out of three trials, both endocrine and exocrine changes associated with reversion from foraging to brood care were induced in colonies composed of all old bees and devoid of brood; JH titers decreased and hypopharyngeal glands regenerated. These results demonstrate that plasticity in age-related division of labor in honey bee colonies is at least partially controlled by social factors. The implications of these results are discussed for the recently developed ‘‘activator-inhibitor” model for honey bee behavioral development.

Physiological correlates of division of labor among similarly aged honey bees

Hormone analyses and exocrine gland measurements were made to probe for physiological correlates of division of labor among similarly aged adult worker honey bees (Apis mellifera L.). Middle-age bees (ca. 2 weeks old) performing different tasks showed significant differences in both juvenile hormone (JH) biosynthesis rates and hemolymph titers; guards and undertakers had high JH, and wax producers and food storers, low JH. Guards and undertakers had similar hormone levels to foragers, even though they were 10 days younger than foragers. No differences in JH were detected among young bees (1-week-old queen attendants and nurses) or older bees (3–4 week-old pollen foragers, non-pollen foragers, and soldiers). Hypopharyngeal gland size was inversely correlated with worker age and rate of JH biosynthesis, but soldiers had significantly larger hypopharyngeal glands than did foragers, despite their similar age and JH level. Results from soldiers indicate that exocrine gland development is not always linked with age-related behavior and endocrine development; they also support the recent claim that soldiers constitute a group of older bees that are distinct from foragers. Hormonal analyses indicate that the current model of JHs role in honey bee division of labor needs to be expanded because high levels of JH are associated with several other tasks besides foraging. JH may be involved in the regulation of division of labor among similarly aged workers in addition to its role in age-related division of labor.

Effects of colony food shortage on behavioral development in honey bees

Abstract Three experiments were conducted to explore the effects of severe food shortage on the control of two important and interrelated aspects of temporal division of labor in colonies of the honey bee (Apis mellifera): the size and age distribution of a colonys foraging force. The experiments were conducted with single-cohort colonies, composed entirely of young bees, allowing us to quickly distinguish the development of new (precocious) foragers from increases in activity of bees already competent to forage. In experiment 1, colony food shortage caused an acceleration of behavioral development; a significantly greater proportion of bees from starved colonies than from fed colonies became precocious foragers, and at significantly younger ages. Temporal aspects of this starvation effect were further explored in experiment 2 by feeding colonies that we initially starved, and starving colonies that we initially fed. There was a significant decrease in the number of new foragers in starved colonies that were fed, detected 1 day after feeding. There also was a significant increase in the number of new foragers in fed colonies that were starved, but only after a 2-day lag. These results suggest that colony nutritional status does affect long-term behavioral development, rather than only modulate the activity of bees already competent to forage. In experiment 3, we uncoupled the nutritional status of a colony from that of the individual colony members. The behavior of fed individuals in starved colonies was indistinguishable from that of bees in fed colonies, but significantly different from that of bees in starved colonies, in terms of both the number and age distribution of foragers. These results demonstrate that effects of starvation on temporal polyethism are not mediated by the most obvious possible worker-nest interaction: a direct interaction with colony food stores. This is consistent with previous findings suggesting the importance of worker-worker interactions in the regulation of temporal polyethism in honey bees as well as other social insects.

Hormonal regulation of behavioural development in the honey bee is based on changes in the rate of juvenile hormone biosynthesis

Abstract In the adult worker honey bee (Apis mellifera L.), increases in the haemolymph titre of juvenile hormone underlie behavioural development, from nest duties to foraging. However, the physiological basis of juvenile hormone titre regulation was unknown. Using a radiochemical assay for juvenile hormone biosynthesis in vitro, we demonstrate that differences in juvenile hormone titres among bees performing different age-dependent tasks are a consequence of changes in rates of hormone synthesis by the corpora allata. Rates of juvenile hormone biosynthesis were low in newly emerged bees, 7–9-day-old nurse bees, and 14–15-day-old bees collected from the nest periphery, and high in foragers. Rates of biosynthesis were highly correlated with haemolymph titres of juvenile hormone measured in the same individuals. Corpora allata contained mostly methyl farnesoate, the immediate precursor of juvenile hormone, and released principally juvenile hormone III into the incubation medium, indicating no appreciable hormone storage. We also report similarities and differences in parameters of juvenile hormone biosynthesis between nurse bees and foragers that were found during the course of a detailed characterization of the radiochemical assay for adult worker honey bees. These results, coupled with the fact that it is possible to measure rates of juvenile hormone biosynthesis from individual bees, indicate that the radiochemical assay will be useful in further studies of hormonal regulation of bee behaviour.

A Meta-Analysis of Effects of Bt Crops on Honey Bees (Hymenoptera: Apidae)

Background Honey bees (Apis mellifera L.) are the most important pollinators of many agricultural crops worldwide and are a key test species used in the tiered safety assessment of genetically engineered insect-resistant crops. There is concern that widespread planting of these transgenic crops could harm honey bee populations. Methodology/Principal Findings We conducted a meta-analysis of 25 studies that independently assessed potential effects of Bt Cry proteins on honey bee survival (or mortality). Our results show that Bt Cry proteins used in genetically modified crops commercialized for control of lepidopteran and coleopteran pests do not negatively affect the survival of either honey bee larvae or adults in laboratory settings. Conclusions/Significance Although the additional stresses that honey bees face in the field could, in principle, modify their susceptibility to Cry proteins or lead to indirect effects, our findings support safety assessments that have not detected any direct negative effects of Bt crops for this vital insect pollinator.

Juvenile hormone titers, juvenile hormone biosynthesis, ovarian development and social environment in Bombus terrestris.

The effects of the social environment and age on juvenile hormone (JH) and reproduction were investigated by measuring ovarian development, hemolymph levels of JH III, and rates of JH biosynthesis from the same individual bumble bees (Bombus terrestris). Differences in social environment were associated with differences in rates of JH biosynthesis, JH titer and ovarian development. Young queenless workers had a higher rate of JH biosynthesis, JH titer and ovarian development than queenright (QR) workers of similar age. Dominant workers in QR colonies had a higher rate of JH biosynthesis, JH titer and ovarian development than low ranked workers of similar size. There was a positive correlation between JH titer and ovarian development, but no correlation between rate of JH biosynthesis and ovarian development or between JH biosynthesis and JH titer. Both JH titer and rate of JH biosynthesis increased with age from emergence to 3 days of age, but 6-day-old workers, egg-laying workers, and actively reproducing queens had high JH titers and highly developed ovaries but low rates of JH biosynthesis. These results show that reproduction in B. terrestris is strongly affected by the social environment and the influence of the environment on reproduction is mediated by JH. Our data also indicate that the rate of JH biosynthesis measured in vitro is not a reliable indicator of JH titer or ovarian development in B. terrestris; possible reasons are discussed.

Physiological and Behavioral Changes in Honey Bees (Apis mellifera) Induced by Nosema ceranae Infection

Persistent exposure to mite pests, poor nutrition, pesticides, and pathogens threaten honey bee survival. In healthy colonies, the interaction of the yolk precursor protein, vitellogenin (Vg), and endocrine factor, juvenile hormone (JH), functions as a pacemaker driving the sequence of behaviors that workers perform throughout their lives. Young bees perform nursing duties within the hive and have high Vg and low JH; as older bees transition to foraging, this trend reverses. Pathogens and parasites can alter this regulatory network. For example, infection with the microsporidian, Nosema apis, has been shown to advance behavioral maturation in workers. We investigated the effects of infection with a recent honey bee pathogen on physiological factors underlying the division of labor in workers. Bees infected with N. ceranae were nearly twice as likely to engage in precocious foraging and lived 9 days less, on average, compared to controls. We also show that Vg transcript was low, while JH titer spiked, in infected nurse-aged bees in cages. This pattern of expression is atypical and the reverse of what would be expected for healthy, non-infected bees. Disruption of the basic underpinnings of temporal polyethism due to infection may be a contributing factor to recent high colony mortality, as workers may lose flexibility in their response to colony demands.

Juvenile hormone profiles of worker honey bees, Apis mellifera, during normal and accelerated behavioural development

Juvenile hormone III (JH) haemolymph titres were quantified in adult worker honey bees under colony conditions conducive to either typical or accelerated behavioural development. JH titres of bees under conditions of accelerated behavioural development were significantly higher than same-aged bees under more typical conditions, even before the onset of foraging. These results are consistent with previous findings indicating that JH plays a causal role in timing the onset of foraging behaviour in honey bees. We also detected a peak of JH in 2-3 day old adult bees, the significance of which is unknown.

Sex-Specific Splicing of the Honeybee Doublesex Gene Reveals 300 Million Years of Evolution at the Bottom of the Insect Sex-Determination Pathway

Sex-determination mechanisms vary greatly among taxa. It has been proposed that genetic sex-determination pathways evolve in reverse order from the final step in the pathway to the first step. Consistent with this hypothesis, doublesex (dsx), the most downstream gene in the Drosophila sex-determination cascade that determines most sexual phenotypes also determines sex in other dipterans and the silk moth, while the upstream genes vary among these species. However, it is unknown when dsx was recruited to the sex-determination pathway during insect evolution. Furthermore, sex-specific splicing of dsx, by which dsx determines sex, is different in pattern and mechanism between the moth and the fly, raising an interesting question of how these insects have kept the executor of sex determination while allowing flexibility in the means of execution. To address these questions, here we study the dsx gene of the honeybee Apis mellifera, a member of the most basal lineage of holometabolous insects. We report that honeybee dsx is sex-specifically spliced and that it produces both the fly-type and moth-type splicing forms, indicating that the use of different splicing forms of Dsx in controlling sexual differentiation was present in the common ancestor of holometabolous insects. Our data suggest that in ancestral holometabolous insects the female Dsx form is the default and the male form is generated by suppressing the splicing of the female form. Thus, it is likely that the dsx splicing activator system in flies, where the male form is the default, arose during early dipteran evolution.

Nosema ceranae, a newly identified pathogen of Apis mellifera in the USA and Asia.

Globalization has provided opportunities for parasites/pathogens to cross geographic boundaries and expand to new hosts. Nosema disease is one of the most serious adult honey bee diseases and has high prevalence in honey bee colonies. For years, Nosema apis was thought to be the only microsporidian infecting domestic bee colonies. However, recently it was discovered that N. ceranae could cross the species barrier from Asian honey bees (Apis cerana) to European honey bees (Apis mellifera) that are widely used for crop pollination and honey production. Over the last few years, considerable progress has been made in our understanding of Nosema infections in honey bees. This review summarizes previous findings and recent progress in the understanding of Nosema infection of A. mellifera in the USA and Asia, with particular emphasis on the comparative epidemiological, morphological, pathological, and genomic organization of two Nosema species. The prospects of future research and remaining unresolved questions associated with the study of honey bee Nosema diseases are also discussed.ZusammenfassungNosema ist ein sporenbildender Parasit, der eine ernsthafte Erkrankung der erwachsenen Honigbienen verursacht und von einer Forschergruppe in Zusammenhang mit dem Colony Collapse Disorder (CCD) gebracht wurde. Die Erkrankung wird durch zwei verschiedene Nosema-Arten, N. apis und N. ceranae verursacht. Wir weisen nach, dass N. ceranae der für Bienen in den USA und Asien vorherrschende Erreger ist. Wir präsentieren auch die erste vollständige pathologische, genetische und genomische Analyse dieses Pathogens. Die Informationen aus dieser Arbeit können von anderen Forschern und Sachverständigen genutzt werden, um Bienenvölker auf die Krankheit hin zu untersuchen und um effektive Maßnahmen zu ihrer Bekämpfung zu entwickeln.