The power and efficiency of brood incubation in queenless microcolonies of bumble bees (Bombus terrestris L.)

1. Ground‐nesting colonies of bumble bees incubate their brood at > 30 °C if floral forage provides sufficient energy and the thermogenic power of the colony can counteract cool soil conditions. To explore the basis of incubation, the thermogenic power and sugar consumption of orphaned nests of bumble bee workers (microcolonies) were investigated under laboratory conditions. 2. This study tested experimentally the effect of variation in worker number (ranging from four to 12 adults) on a microcolony's capacity to regulate brood temperature and recover from acute cold exposure. Microcolonies were provided with ad libitum sugar syrup and minimal insulation and maintained at an ambient temperature of c. 25 °C. Energy conversion efficiency was estimated by comparing sugar consumption with the power required for artificial incubation. The joint energetics of foraging and incubation were modelled in wild colonies to explore the effect of colony size and landscape quality on thermoregulation. 3. The results showed that all sizes of microcolonies regulated brood temperature at c. 31 °C under laboratory conditions, which required 96 mW of thermogenic power. It was estimated that individual workers of B. terrestris generated an incubatory power of 35 mW. The smallest microcolonies had the highest conversion efficiency (57%), apparently because few workers were required for incubation. 4. Modelling indicated that small microcolonies of three to seven adult workers have the capacity for normal brood incubation in the wild, but that the minimum viable colony size increases as floral forage becomes poorer or more distant. 5. These preliminary findings suggest the feasibility of identifying the minimum conditions (forage quality, soil temperature, and colony size) necessary for brood incubation by queenright colonies in the wild.     

Sexual biology of haploid and diploid males in the bumble beeBombus terrestris

Summary InB. terrestris diploid males develop normally into adults (Duchateau et al., 1994). The diploid males are similar in appearance to the haploid males, except that they are smaller. The size of the testis of diploid males, relative to the length of the radial cell, is smaller than that of haploid males. There is overlap in the frequency distribution with respect to body size and testis size. The spermatozoa of diploid males are larger than those of the haploids and the vasa deferentia contain fair less spermatozoa than those of haploid males of the same age. Countings and measurements of the spermatozoa, therefore, can give the best indication about the ploidy of the males. Diploid males are successful in mating. They mate at a younger age than haploid males and they die sooner. The number of vial offspring of diploid males, however, is very low. No queen that mated with a diploid male produced a colony, but a few queens did produce some progeny. These might have been triploid males and workers. InB. terrestris higher ploidy results in smaller individuals, whereas in several other species of the Hymenoptera it has been found to result in larger individuals.     

Perception,regulation, and fitness effects of pollen phytosterols in the bumble bee,Bombus terrestris

Premise

Many flowering plants depend on insects for pollination and thus attract pollinators by offering rewards, mostly nectar and pollen. Bee pollinators rely on pollen as their main nutrient source. Pollen provides all essential micro- and macronutrients including substances that cannot be synthesized by bees themselves, such as sterols, which bees need for processes such as hormone production. Variations in sterol concentrations may consequently affect bee health and reproductive fitness. We therefore hypothesized that (1) these variations in pollen sterols affect longevity and reproduction in bumble bees and (2) can thus be perceived via the bees' antennae before consumption.

Methods

We studied the effect of sterols on longevity and reproduction of Bombus terrestris workers in feeding experiments and investigated sterol perception using chemotactile proboscis extension response (PER) conditioning.

Results

Workers could perceive several sterols (cholesterol, cholestenone, desmosterol, stigmasterol, β-sitosterol) via their antennae but not differentiate between them. However, when sterols were presented in pollen, and not as a single compound, the bees were unable to differentiate between pollen differing in sterol content. Additionally, different sterol concentrations in pollen neither affected pollen consumption nor brood development or worker longevity.

Conclusions

Since we used both natural concentrations and concentrations higher than those found in pollen, our results indicate that bumble bees may not need to pay specific attention to pollen sterol content beyond a specific threshold. Naturally encountered concentrations might fully support their sterol requirements and higher concentrations do not seem to have negative effects.

     

Brain biogenic amines and reproductive dominance in bumble bees (Bombus terrestris)

To begin to explore the role of biogenic amines in reproductive division of labor in social insects, brain levels of dopamine, serotonin, and octopamine were measured in bumble bee (Bombus terrestris) workers and queens that differ in behavioral and reproductive state. Levels of all three amines were similar for mated and virgin queens. Young workers that developed with or without a queen had similar amine levels, but in queenright colonies differences in biogenic amine levels were associated with differences in behavior and reproductive physiology. Dominant workers had significantly higher octopamine levels compared with workers of lower dominance status but of similar size, age, and ovary state. High dopamine levels were associated with the last stages of oocyte development irrespective of worker social status and behavior. These results suggest that biogenic amines are involved in behavioral and physiological aspects of regulation of reproduction in bumble bees. Accepted: 10 December 1999     

Alternative splicing associated with phenotypic plasticity in the bumble bee Bombus terrestris

Phenotypic plasticity is when one genome can produce more than one phenotype. The caste system found in many social insects is an important example of plasticity. Several studies have examined gene expression in social insect developmental and caste differences. Changes in gene expression, however, are not the only source of phenotypic plasticity. Here, we investigate the role of alternative splicing in the buff‐tailed bumble bee Bombus terrestris. We found that 5,458 genes in B. terrestris (40%) express more than one isoform. Larvae have the lowest level of splicing events, followed by adults and then pupae. We found that when an isoform is expressed in a given caste in the larval stage, it tends to be expressed in all castes at the larval stage. The same is true at the pupal stage. However, we see more complicated interactions between the adult castes with reproductive females showing different isoform expression compared to nonreproductive females and male adults showing the most distinct patterns. We found 455 isoform switching genes, that is genes, where one developmental stage, sex or caste uses a specific isoform and another type uses a different isoform. Among genes displaying isoform switching are some involved in the ecdysteriod pathway, an important system in insect behaviour.     

Lateralization in the invertebrate brain: left-right asymmetry of olfaction in bumble bee, Bombus terrestris

Brain and behavioural lateralization at the population level has been recently hypothesized to have evolved under social selective pressures as a strategy to optimize coordination among asymmetrical individuals. Evidence for this hypothesis have been collected in Hymenoptera: eusocial honey bees showed olfactory lateralization at the population level, whereas solitary mason bees only showed individual-level olfactory lateralization. Here we investigated lateralization of odour detection and learning in the bumble bee, Bombus terrestris L., an annual eusocial species of Hymenoptera. By training bumble bees on the proboscis extension reflex paradigm with only one antenna in use, we provided the very first evidence of asymmetrical performance favouring the right antenna in responding to learned odours in this species. Electroantennographic responses did not reveal significant antennal asymmetries in odour detection, whereas morphological counting of olfactory sensilla showed a predominance in the number of olfactory sensilla trichodea type A in the right antenna. The occurrence of a population level asymmetry in olfactory learning of bumble bee provides new information on the relationship between social behaviour and the evolution of population-level asymmetries in animals.     

Ecdysteroid titer, ovary status, and dominance in adult worker and queen bumble bees (Bombus terrestris)

The role of ecdysteroids in the regulation of dominance and reproduction in social Hymenoptera is little explored. In the current study we compared ecdysteroid titers in hemolymph of individual queen and worker bumble bees (Bombus terrestris) that differ in their behavior, reproductive status and social environment. Egg-laying queens that head colonies and have ovaries exhibiting all stages of follicle development, had a higher ecdysteroid titer than virgin queens whose ovaries contained only follicles at initial stages. In workers, the relationship between ecdysteroid titers and follicle development appears to be more complex and to be influenced by the bee's social status and social environment. Shortly after emergence, young workers had only follicles at the initial stages of oogenesis and they exhibited a low ecdysteroid titer. No significant correlation was detected between ovary status and ecdysteroid titer in workers, with some workers showing activated ovaries but low ecdysteroid titers. However, at six days of age, a trend towards higher ecdysteroid titer was observed for workers in queenless groups, a condition characterized by rapid follicle development relative to queenright conditions. In these queenless groups, high social status was associated with high ecdysteroid titers. By contrast, in queenright workers ecdysteroid titers were low, even for bees with presumably high social status that had activated ovaries and were observed performing oviposition behavior. This study suggests that ecdysteroids are involved in regulation of reproduction in B. terrestris.     

In vivo dynamics of an immune response in the bumble bee Bombus terrestris

Concepts from evolutionary ecology have recently been applied to questions of immune defences. However, an important but often neglected aspect is the temporal dynamics of the simple immune measures used in ecological studies. Here, we present observations for workers of the bumble bee Bombus terrestris on the dynamics of the phenoloxidase (PO) system, antibacterial activity, and the total number of haemocytes following a challenge with immune elicitors (LPS, Laminarin), over a time-span ranging from 1min to 14 days. The dynamics of the PO measurement showed a complex pattern and was correlated with haemocyte counts. Antibacterial activity, on the other hand, increased sharply between 2 and 24h post-challenge followed by a slow decrease. Surprisingly, the effects of a challenge lasted up to 14 days.     

Reproductive division of labor, dominance, and ecdysteroid levels in hemolymph and ovary of the bumble bee Bombus terrestris

To determine whether ecdysteroids are associated with reproductive division of labor in Bombus terrestris, we measured their levels in hemolymph and ovaries of queens and workers. Queens heading colonies had large active ovaries with high ecdysteroid content, whereas virgin gynes and mated queens before and after diapause had undeveloped ovaries with low ecdysteroid content. The hemolymph ecdysteroid titer was rather variable, but in a pooled analysis of mated queens before and after diapause versus colony-heading queens, ecdysteroid titers were higher in the latter group. In workers, agonistic behavior, ovarian activity, ovarian ecdysteroid content, and hemolymph ecdysteroid titers were positively correlated, and were lowest when a queen was present. In queenless workers, ecdysteroid levels were elevated in dominant workers, and were also influenced by the presence of brood and by group demography; hormone levels were higher in bees kept in larger groups. These findings are consistent with the premise that in B. terrestris the ovary is the primary site of ecdysteroid synthesis, and they show that ecdysteroids levels vary with the social environment.     

The safety of thiamethoxam to pollinating bumble bees (Bombus terrestris L.) when applied to tomato plants through drip irrigation

Thiamethoxam, mainly sold under the trademark of Actara, is a neonicotinoid widely used in covered vegetables for the control of aphids and whiteflies. In these crops, and particularly in covered tomatoes, bumble-bees are used for cross-pollination as an alternative to labour intensive manual techniques. In this study, made on tomatoes grown in separated greenhouse plots in Murcia, Southern Spain, thiamethoxam was applied through drip irrigation at a rate of 200 g ai/ha, and as a split application of the same rate, to evaluate the effects on pollinating bumble bees compared to a foliar application of a toxic standard. The results showed that the toxic foliar standard had a clear effect on the pollination of tomato flowers, declining to zero pollination two weeks after application, whereas both the single and split drip irrigation applications of Actara had no effect on pollination when compared to the control plots. The count of dead adults and larvae did not show any differences between the treatments, whereas the measurement of sugar water consumption was shown to correlate well with pollination. The consumption of sugar water declined in the toxic standard plots by 69% with respect to the control, whilst the decline in lower dose drip irrigation application was only 3%. In regard to hive weight, and number of adults and brood after destructive sampling; there were no statistical differences between the treatments but a negative effect of the foliar treatment was observed. Based on these results we can conclude that a split application of Actara applied in drip irrigation to the soil/substrate has no effect on the bumble-bees used in tomatoes for pollination.     

Imprinting, digoxin uptake and storage in Tetrahymena

Tetrahymenas after a single exposure to high concentration of digoxin, release glycoside into the culture medium even three days after removal of the drug. After nine or fifteen days, however, this effect subsides. Re-administration of digoxin causes the digoxin consumption (storage) of Tetrahymenas to increase. This observation indicates that the digoxin imprinting previously demonstrated in mammals occurs also in Tetrahymena. The experiments raise the possibility that also Tetrahymenas are capable of producing a digoxin-like substance detectable by radioimmunoassay.     

Die Wasserstoffionenkonzentration im Darm von Lumbricus terrestris L.

Zusammenfassung Die Reaktion des Darminhalts normal gehaltener Regenwürmer (stets Lumbricus terrestris L.) wurde mit drei verschiedenen Methoden geprüft. Indikatorstreifchen in den Darminhalt eingesenkt, Chinhydronelektrode und Glaselektrode (bei der Verdünnung 11) ergeben übereinstimmende Werte. Im Zusammenhang mit der schlechten Pufferung des Darminhalts schwanken die Werte bei verschiedenen Tieren nicht unbeträchtlich. Trotz dieser Schwankungen gliedert sich die Reaktion in aufeinanderfolgenden Darmabschnitten bei jedem Tier gesetzmäßig. Auf den alkalischen Pharynx (6,9–7,8; im Mittel 7,3) folgt der schwach saure bis schwach alkalische Drüsen- und Muskelmagen (6,7–7,6; im Mittel 7,0). Der Anfangsabschnitt des Intestinums (18.–40. Segment) ist bei allen untersuchten Tieren der sauerste Abschnitt (6,47–7,23; im Mittel 6,8); im 40.–60. Segment findet man eine mittlere Reaktion von 7,2, im 60.–80. Segment erreicht der Intestinuminhalt den alkalischsten Punkt (7,65–8,05, im Mittel 7,9), um von hier an wieder abzufallen: 7,1 im 80.–100. Segment (6,82–7,30) und 7,3 im 100. bis zum 120. Segment (7,03–7,37).     

Mikroanatomic des Bauchmarks von Lumbricus terrestris L. (Annelida,Oligochaeta)

Zusammenfassung Die Nervenzellen and -bahnen der Bauchmarkganglien von Lumbricus terrestris wurden in osmiumfixierten Serienquersehnitten möglichst vollständig identifiziert and eingehend besehrieben. Folgende Gruppen lassen sich trennen:In jeder Bauchmarkseite wurden 5 Bündel von sensorischen, anscheinend aus den Epidermissinnesorganen stammenden Fasern lokalisiert (SLB). Sie sind mit den von Coggeshall (1965) elektronenoptiseh dargestellten and als Neuropil bezeiehneten Fäserchen von nur 0,I bis 0,3 m Durchmesser identisch.Die Zellsomata der ventralen Riesenfasern (VRF) wurden aufgefunden. Diese Fasern bestehen ebenso wie die dorsalen RF aus unizellulären, rich über eine lange Strecke überlappenden, segmentalen Abschnitten. Sie stehen in enger morphologischer Beziehung zu einem der sensorischen Längsbündel.Die identifizierten Bauchmarkneurone mitperipherwärtsverlaufenden Axonen (PN) wurden in 4 Gruppen unterteilt: Die PN1 Bind hoterolaterale, monopolare Neurone mit Kollateralen im dorsalen Neuropil; ihre Axone verlassen das Bauchmark durch alle 3 Seitennerven-Paare. PN2, PN3 and PN4 sind homolaterale Neurone mit Kollateralen im ventralen Neuropil. PN2 and PN4 sind monopolar ; ihre Axone treten durch die SN3 des gleichen bzw. des vorangehenden Segments aus dem Bauchmark. Die PN3 sind bipolar, gelegentlich tripolar ; ihre Axone verlassen das Bauchmark durch 2 (bzw. 3) SN, eines stets durch den SN3 des gleichen Segments, das (oder die beiden) andere(n) durch den SN1 des gleichen oder (und) des nachfolgenden Segments. Lage, Anzahl und Cytologie der in Gruppen vorkommenden PN-Somata werden eingehend geschildert.Die Interneurone des Bauchmarks (IN; RF nicht einbegriffen) werden drei Hauptgruppen zugeordnet : Der größere Teil der IN (über die Hälfte aller Bauchmarkneurone) besteht aus kleinen Neuronen mit kurzen, sich our in das homolaterale Neuropil erstreckenden Fasern (KIN). Die zweite Gruppe wird von größeren Interneuronen gebildet (GSIN), die anscheinend streng metamer und symmetrisch in beiden Ganglionhälften vorkommen. Sie machen je nach Körperregion aller Neurone des Ganglions aus. Ihre homo- oder heterolateralen Axone können in Längsrichtung intra- oder intersegmental oft über eine Segmentlänge hin verfolgt werden. Die dritte Gruppe wird von polysegmentalen IN (PSIN) gebildet, mit sehr großen Zellkörpern, die weder metamer noch bilateral-symmetrisch angeordnet sind. Die Axone erstrecken sich polysegmental über mindestens 30 Segmente und bilden auffällige Hauptfaserzüge (HFZ) in der Peripherie der Faserregion des Bauchmarks.Zuletzt wird die Anzahl und Verteilung der Neurone in Ganglien verschiedener Bauchmarkregionen angegeben und mit der Anzahl der Nervenfasern in den Konnektiven verglichen. Die Anzahl der kleinen Interneurone (KIN) ist je nach Bauchmarkregion sehr unterschiedlich, während die übrigen Neurone regelmäßig auftreten.In der Diskussion wird einerseits die morphologische und cytologische Konstanz vieler Einzelelemente im Regenwurmbauchmark hervorgehoben und auf die funktionellen Konsequenzen hingewiesen. Außerdem wird versucht, durch Vergleich mit Angaben über andere Tierarten und Gegenüberstellung morphologischer und funktioneller Befunde allgemeine Prinzipien für den Zusammenhang zwischen Struktur und Funktion im Bauchmarkaufbau herauszustellen.

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Microanatomy of the Ventral Nerve Cord of Lumbricus terrestris L. (Annelida, Oligoehaeta)

Nerve cells and tracts in the ventral nerve cord of the earthworm Lumbricus terrestris are thoroughly described and partly individually identified: sensory bundles, ventral giant fibers, central neurons with peripheral axons and various types of interneurons are recognized.

     

Neurosecretion. XII. The formation of neurosecretory granules in the earthworm,Lumbricus terrestris L.

Summary The granules of neurosecretory cells in the supraesophageal ganglion of the earthworm, Lumbricus terrestris L., are formed by the Golgi apparatus. The process of neurosecretion is discussed in relation to this observation.This research was aided by grants (B-840, B-2145 and 2M-6418) of the United States Public Health Service.