Wolf Engels

2 Social Insect Polymorphism: Hormonal Regulation of Plasticity in Development and Reproduction in the Honeybee

Publisher Summary This chapter discusses the hormonal regulation of plasticity in development and reproduction in the honeybee. The insight that hormones may be the cornerstones for understanding the developmental regulation, not only in preimaginal caste differentiation but also in adult life, has turned honeybee into a model for studies on caste in social insects, the reasons being its relatively large size and its ready availability together with a wealth of knowledge concerning honeybee biology and management. More recent views on caste differentiation seek to understand the developmental regulation in honeybee in the context of metamorphosis, particularly focusing on the role of the morphogenetic hormones, juvenile hormone, and ecdysone. These hormones exert additional and apparently novel functions in the adult life of honeybee. Reproduction and division of labor are also discussed in the chapter in the context of endocrine regulation. Long-term integration of the developmental processes and reproduction cycles with environmental conditions poses a key problem for any organism. In general, the required interaction of external stimuli with the genotype of an organism is mediated and orchestrated by hormones. During critical periods of caste differentiation, research on the regulatory pathways in the endocrine system of the honeybee larvae has shown that the corpora allata exhibit a caste-specific program of activity during the last larval instar and that this program can set the activity pattern of the prothoracic gland.

Caste Development, Reproductive Strategies, and Control of Fertility in Honey Bees and Stingless Bees

In the highly eusocial honey bees (Apinae) and stingless bees (Meliponinae) marked caste syndromes have evolved. The typical queen and worker characteristics are different from one another not just with regard to the reproductive organs but include many other morphological, physiological, and behavioral differences as well. These striking caste distinctions are the result of postembryonic divergences in development which depend on ecological conditions, mainly on the external factor of larval nutrition. Caste development in social insects in general belongs to the widespread phenomena of insect polymorphism and, in accordance with environmental control, castes in bees were called ecomorphs (de Wilde and Wirtz 1974; de Wilde 1975). The trophogenic basis for caste induction is provided by the nursing workers, although in a colony brood rearing including gyne production is strongly influenced by the queen. The queen also rigidly controls all reproduction of the workers. On the other hand, her own reproductive output depends completely on the helper functions of the workers, her daughters.

Primer effect of queen pheromone on juvenile hormone biosynthesis in adult worker honey bees

Juvenile hormone synthesis in adult worker honey bees was measured by an in vitro corpora allata bioassay. Adult queenless workers exhibit higher rates of juvenile hormone biosynthesis than queenright workers. Hormone synthesis is not correlated with the volume of the glands. Extract of queen mandibular glands, applied to a dummy, reduces juvenile hormone biosynthesis in caged queenless workers to the level of queenright workers. The same result was obtained with synthetic (E)-9-oxo-2-decenoic acid, the principal component of the queen mandibular gland secretion. This pheromonal primer effect may function as a key regulating element in maintaining eusocial colony homeostasis. The presence of brood does not affect the hormone production of the corpora allata.

Stomach-flushing for diet analysis in anurans: an improved protocol evaluated in a case study in Araucaria forests, southern Brazil*

Stomach-flushing is a gentle treatment in analysing the diet of vertebrates. We applied this method in the study of seasonal nutrition of anurans of 15 species at an Araucaria forest habitat on the Serra Geral of Rio Grande do Sul, Brazil. Over 500 frogs and toads of different body size were handled in order to evaluate an improved protocol without narcosis using soft infusion tubes in order to avoid negative effects of the flushing procedure. The specimens were treated soon after capture and then returned to the sampling sites. Our results are discussed with reference to the few studies on stomach flushing in amphibians. The improved technique is recommended to avoid killing of numerous animals for nutritional studies, in particular because of the worldwide threatening of amphibian populations.

Not Only Single Mating in Stingless Bees

Abstract. Queens of the large, pantropical and fully eusocial taxon Meliponinae (stingless bees) are generally considered to be singly mated. We indirectly estimated queen mating frequency in two meliponids, Melipona beecheii and Scaptotrigona postica, by examining genotypes of workers at microsatellite DNA loci. Microsatellites were highly variable, providing suitable markers with which to assign patrilinial origin of workers within colonies headed by single queens. Queen mating frequency varied between 1 and 3 (M. beecheii) and 1 and 6 (S. postica), representing the first clear documentation of polyandry in the Meliponinae. Effective paternity frequency, me, was lower, although above 2 for S. postica. Stingless bees may provide suitable subjects for the testing of recent inclusive fitness arguments describing intracolony kin conflict in social Hymenoptera.

Caste determination is a sequential process: effect of larval age at grafting on ovariole number, hind leg size and cephalic volatiles in the honey bee (Apis mellifera carnica)

SUMMARYArtificial queen rearing with worker larvae grafted at different developmental stages resulted in gradual effects on ovary size (number of ovarioles per ovary), as well as hind leg and wax gland structures in adults. A significant decrease in ovariole number was observed when third instar larvae were grafted. Basitarsus shape was affected when fourth instar larvae were grafted. Queen—worker intermediates developed when early-fifth instar worker larvae were transferred. As newly emerged adults, spectra of cephalic volatiles of queens and workers are still very similar, and do not yet exhibit the caste-specific elements of the mandibular glands. At one day after emergence, most of the dominant compounds in these spectra are represented at higher levels in workers.

Developmental patterns of vitellogenin haemolymph titre and rate of synthesis in adult drone honey bees (Apis mellifera)

Abstract In adult drones temporal changes in the protein content of the haemolymph were determined showing a maximal concentration during the first week after emergence. In this period vitellogenin was found to represent about 5% of the soluble haemolymph proteins. Tracer experiments revealed that the maximal vitellogenin production makes up about 10% of the total synthesis of serum proteins until day 8 and decreases rapidly thereafter. In drones older than 2 weeks, only traces of vitellogenin could be detected in the haemolymph and vitellogenin synthesis ceased. This developmental pattern is compared with worker bees and discussed under the aspects of drone maturation and expression of a female-specific gene in a male genomic environment as realized in the haplo-diploid hymenoptera.

Identification of oxygen containing volatiles in cephalic secretions of workers of Brazilian stingless bees

Os constituintes volateis das secrecoes cefalicas de 11 especies brasileiras de abelhas sem ferrao da linha Tetragonisca - Tetragona foram analisados. Foram identificados 145 compostos, por cromatografia gasosa e espectrometria de massas, dentre os quais 72 esteres, 22 alcoois, 16 acidos carboxilicos, 13 terpenos, 8 aldeidos, 4 compostos aromaticos, 2 lactonas e 1 diidropirano. As relacoes estruturais, origem e a distribuicao detes compostos sao discutidas. Com respeito a composicao qualitativa e quantitativa, cada especie mostra um buque de odores, os quais sao obtidos a partir de componentes poucos especificos. Em algumas especies proximamente relacionadas foram observadas similaridades no buque de odores. As fragmentacoes no espectro de massas de esteres graxos e dos esteres insaturados derivatizados com DMDS sao discutidas em detalhes.

Differential hygienic behaviour towards Varroa jacobsoni in capped worker brood of Apis cerana depends on alien scent adhering to the mites

SUMMARYFive Apis cerana colonies in Newton hives in Allahabad, northern India, were used in the experiments. Female Varroa jacobsoni, in the reproductive phase, were transferred from drone brood into worker brood in the same colony (1), or into worker brood in another colony (2). Some introductions (3) involving dead mites washed with ethanol and pentane (and therefore odour-free) were also carried out. Mites collected from a single Apis mellifera colony were introduced into some A. cerana brood (4), and some ‘sham inoculations’, involving the opening and closing of brood cells without the introduction of a mite, were made (5). After 5 days, in (1) and (5) only about 10% of manipulated cells were found empty. In (1) and (3), in addition, about 40% of cells had been opened, the mites removed, and the cells, still containing pupae, resealed. About 50% of manipulated cells were untouched. The percentage of empty cells was much higher in (2), and even higher in (4). The results indicate that differences in hy...

Thermoregulation in the nest of the Neotropical Stingless bee Scaptotrigona postiça and a hypothesis on the evolution of temperature homeostasis in highly Eusocial bees

In the Brazilian stingless bee, Scaptotrigona postica, social thermoregulation was studied. Intranidal temperature was recorded in different parts of the nest and related to changes in ambient temperature. In addition, cooling and overheating experiments were carried out using colonies in laboratory observation hives. The brood chamber is the warmest part of the nest, well insulated by a multi‐layered involucrum. In the brood nest 32 ± 3° C were measured. In case of low aerial temperature the bees are capable of heating up the brood combs by mass incubation. In addition, cold spots around the brood chamber are insulated by covering with cerumen, and the entrance is more or less closed. Overheating of the brood is reduced by accelerated and aligned fanning and withdrawal of all the bees from the combs. Any direct cooling by evaporation of water could not be observed and probably is not needed in natural nests of Sc. postica which are built in trunk cavities of old trees in the neotropical rain forest. The ...