Yongliang Fan

Genome-wide analysis reveals differences in brain gene expression patterns associated with caste and reproductive status in honey bees (Apis mellifera).

A key characteristic of eusocial species is reproductive division of labour. Honey bee colonies typically have a single reproductive queen and thousands of sterile workers. Adult queens differ dramatically from workers in anatomy, physiology, behaviour and lifespan. Young female workers can activate their ovaries and initiate egg laying; these ‘reproductive’ workers differ from sterile workers in anatomy, physiology, and behaviour. These differences, however, are on a much smaller scale than those observed between the queen and worker castes. Here, we use microarrays to monitor expression patterns of several thousand genes in the brains of same‐aged virgin queens, sterile workers, and reproductive workers. We found large differences in expression between queens and both worker groups (~2000 genes), and much smaller differences between sterile and reproductive workers (221 genes). The expression patterns of these 221 genes in reproductive workers are more queen‐like, and may represent a core group of genes associated with reproductive physiology. Furthermore, queens and reproductive workers preferentially up‐regulate genes associated with the nurse bee behavioural state, which supports the hypothesis of an evolutionary link between worker division of labour and molecular pathways related to reproduction. Finally, several functional groups of genes associated with longevity in other species are significantly up‐regulated in queens. Identifying the genes that underlie the differences between queens, sterile workers, and reproductive workers will allow us to begin to characterize the molecular mechanisms underlying the evolution of social behaviour and large‐scale remodelling of gene networks associated with polyphenisms.

Drosophila melanogaster sex peptide stimulates juvenile hormone synthesis and depresses sex pheromone production in Helicoverpa armigera

Previous studies demonstrate that virgin female adult Helicoverpa armigera (Lepidoptera: Noctuidae) moths exhibit calling behaviour and produce sex pheromone in scotophase from the day after emergence, and that mating turns off both of these pre-mating activities. In the fruit fly Drosophila melanogaster, a product of the male accessory glands, termed sex peptide (SP), has been identified as being responsible for suppressing female receptivity after transfer to the female genital tract during mating. Juvenile hormone (JH) production is activated in the D. melanogaster corpus allatum (CA) by SP in vitro. We herein demonstrate cross-reactivity of D. melanogaster SP in the H. armigera moth: JH production in photophase virgin female moth CA in vitro is directly activated in a dose-dependent manner by synthetic D. melanogaster SP, and concurrently inhibits pheromone biosynthesis activating neuropeptide (PBAN)-activated pheromone production by isolated pheromone glands of virgin females. Control peptides (locust adipokinetic hormone, AKH-I, and human corticotropin, ACTH) do not inhibit in vitro pheromone biosynthesis. Moreover, SP injected into virgin H. armigera females, decapitated 24 h after eclosion, or into scotophase virgin females, suppresses pheromone production. In the light of these results, we hypothesize the presumptive existence of a SP-like factor among the peptides transmitted to female H. armigera during copulation, inducing an increased level of JH production and depressing the levels of pheromone produced thereafter.

Common functional elements of Drosophila melanogaster seminal peptides involved in reproduction of Drosophila melanogaster and Helicoverpa armigera females.

Sex peptide (SP) and Ductus ejaculatorius peptide (Dup) 99B are synthesized in the retrogonadal complex of adult male Drosophila melanogaster, and are transferred in the male seminal fluid to the female genital tract during mating. They have been sequenced and shown to exhibit a high degree of homology in the C-terminal region. Both affect subsequent mating and oviposition by female D. melanogaster. SP also increases in vitro juvenile hormone (JH) biosynthesis in excised corpora allata (CA) of D. melanogaster and Helicoverpa armigera. We herein report that the partial C-terminal peptides SP(8-36) and SP(21-36) of D. melanogaster, and the truncated N-terminal SP(6-20) do not stimulate JH biosynthesis in vitro in CA of both species. Both of these C-terminal peptides reduce JH-III biosynthesis significantly. Dup99B, with no appreciable homology to SP in the N-terminal region, similarly lacks an effect on JH production by H. armigera CA. In contrast, the N-terminal peptides - SP(1-11) and SP(1-22) - do significantly activate JH biosynthesis of both species in vitro. We conclude that the first five N-terminal amino acid residues at the least, are essential for allatal stimulation in these disparate insect species. We have previously shown that the full-length SP(1-36) depresses pheromone biosynthesis in H. armigera in vivo and in vitro. We now show that full-length Dup99B and the C-terminal partial sequence SP(8-36) at low concentrations strongly depress (in the range of 90% inhibition) PBAN-stimulated pheromone biosynthesis of H. armigera. In addition, the N-terminal peptide SP(1-22), the shorter N-terminal peptide SP(1-11) and the truncated N-terminal SP(6-20) strongly inhibit pheromone biosynthesis at higher concentrations.

Hydrocarbon synthesis by enzymatically dissociated oenocytes of the abdominal integument of the German Cockroach, Blattella germanica

In insects, hydrocarbons waterproof the cuticle, protect the insect from the external environment, and serve as semiochemicals or their metabolic precursors. In the German cockroach, Blattella germanica, hydrocarbons are synthesized by the abdominal integument, but the precise site of biosynthesis is not known. We developed a method for separation of oenocytes from other cells in the abdominal integument using enzymatic dissociation followed by Percoll gradient centrifugation. Radiolabeled propionate was then used to monitor de novo synthesis of hydrocarbons by dissociated cells. Oenocyte-enriched cell suspensions of abdominal sternites synthesized hydrocarbons, whereas suspensions enriched with epidermal cells did not. Our results show conclusively that hydrocarbons are produced by oenocytes not only in insects whose oenocytes are localized within the hemocoel, but also in those insects whose oenocytes are within the abdominal integument. Furthermore, these data support a hemolymph pathway for transport and delivery of hydrocarbons to both external and internal tissues, including the epicuticle, fat body, and ovaries.

Juvenile hormone induction of pheromone gland PBAN-responsiveness in Helicoverpa armigera females

The maturation of corpora allata (CA) and the competence of pheromone glands in the adult moth Helicoverpa armigera, are both age-related and appear to be correlated. Sex pheromone glands of pharate adults do not produce sex pheromone independently, nor do they respond to exogenous PBAN. Newly emerged moths produce significantly less pheromone than day one moths. JH (juvenile hormone) II was found to be the main JH form produced by CA in vitro. JH II primed pheromone glands of pharate adults to respond to PBAN. In addition, injection or topical application of JH II to newly-emerged females induced pheromone production in the presence of PBAN. Our findings suggest that JH is involved in the initiation of pheromone production of Helicoverpa armigera.

EFFECT OF PBAN ON PHEROMONE PRODUCTION BY MATED Heliothis virescens AND Heliothis subflexa FEMALES

Mated female Heliothis virescens and H. subflexa were induced to produce sex pheromone during the photophase by injection of pheromone biosynthesis activating neuropeptide (PBAN). When injected with 1 pmol Hez-PBAN, the total amount of pheromone that could be extracted from glands of mated females during the photophase was similar to that extracted from virgin females in the scotophase. The PBAN-induced profile of pheromone components was compared between mated, PBAN-injected females and virgin females during spring and fall. Virgin females exhibited some differences in the relative composition of the pheromone blend between spring and fall, but no such temporal differences were detected in PBAN-injected, mated females. Because the temporal variation in pheromone blend composition was greater for virgin females than for PBAN-injected females, PBAN can be used to determine a female’s native pheromone phenotype. This procedure has the advantages that pheromone glands can be extracted during the photophase, from mated females that have already oviposited.

Tissue localization and regulation by juvenile hormone of human allergen Bla g 4 from the German cockroach, Blattella germanica (L.)

The German cockroach, Blattella germanica (L.), produces several potent protein aeroallergens, including Bla g 4, a ∼20 kDa lipocalin. RT‐PCR, Northern analyses and in situ hybridization showed that Bla g 4 is expressed only in the adult male reproductive system. Western blotting and ELISA with rBla g 4 antiserum detected immunoreactivity in the utricles and the conglobate gland, but not in other tissues of the male reproductive system. The Bla g 4 protein content of males increased from adult emergence to day 14, but during copulation Bla g 4 was depleted in the male and transferred to the female within the spermatophore. Topical application of juvenile hormone III stimulated Bla g 4 production by both conglobate gland and utricles.

Regulation of pheromone biosynthesis, transport, and emission in cockroaches

Publisher Summary This chapter discusses sex pheromones, which are used in mate finding and recognition. The chapter describes the reproductive modes in cockroaches and then presents a conceptual framework for neuroendocrine regulation of cockroach reproductive biology. Blattodea is divided into five families, out of which Blattidae, Blattellidae, and Blaberidae contain most of the cockroach species. This diverse group of insects exhibits a variety of reproductive strategies including obligatory and facultative parthenogenesis, oviparity, ovoviviparity, and viviparity. The reproductive cycle in cockroaches is regulated by several lipid and peptide hormones, with juvenile hormone III (JH III), a C16 sesquiterpenoid, being the critical adult gonadotropic hormone. JH III stimulates the fat body to produce vitellogenin, which is a yolk protein precursor and the oocytes to endocytose vitellogenin. Behavioral and physiological events related to mate finding and sexual receptivity are also regulated in a coordinated manner by this vital hormone. The chapter also discusses pheromone production in several of the best studied species, reviewing for each what is known about the tissues, biochemical pathways, transport routes, and neuroendocrine regulation of pheromone production.

Effects of queen mandibular pheromone on nestmate recognition in worker honeybees, Apis mellifera

The ability to distinguish between members of a social group and unfamiliar individuals is a critical element of social behaviour. Social insects can differentiate between nestmates and non-nestmates via recognition cues, which in most species are cuticular hydrocarbons. Cuticular hydrocarbon patterns are altered by genotype and environmental conditions, but it is unclear whether colony social conditions can also affect nestmate interactions. Honeybee queens produce pheromones that regulate many aspects of worker behaviour, physiology and colony organization. A five-component blend, queen mandibular pheromone (QMP), produces many of the effects of a live queen. We found that QMP treatment alters how resident bees interact with intruder bees, based on standard nestmate recognition assays. However, QMP does not appear to alter the ability of bees to distinguish between nestmates and non-nestmates, or general aggression levels. Rather, QMP exposure significantly alters cuticular hydrocarbon patterns of worker bees, suggesting that QMP-treated nestmates are no longer recognized as nestmates by untreated bees, and vice versa. Thus, queen pheromone can have significant effects on nestmate recognition and interactions in honeybees, which may be important for colony cohesion.

Cuticular hydrocarbons as maternal provisions in embryos and nymphs of the cockroach Blattella germanica.

SUMMARY Cuticular hydrocarbons of arthropods serve multiple functions, including as barriers to water loss and as pheromones and pheromone precursors. In the oviparous German cockroach, Blattella germanica, long-chain hydrocarbons are produced by oenocytes within the abdominal integument and are transported by a blood lipoprotein, lipophorin, both to the cuticular surface and into vitellogenic oocytes. Using radiotracer approaches, we tracked the location and metabolic fate of 14C- and 3H-labeled hydrocarbons through vitellogenic females and their embryos and nymphs. A considerable amount (∼50%) of radiolabeled maternal hydrocarbons was transferred to oocytes and persisted through a 20-day embryogenesis and the first two nymphal stadia. The maternal hydrocarbons were not degraded or lost during this protracted period, except for significant losses of cuticular hydrocarbons starting with the first-to-second instar molt. Thus, although embryos and nymphs can produce their own hydrocarbons, maternal hydrocarbons provide a significant fraction of the cuticular and hemolymph hydrocarbons of both stages. These results show, for the first time in any insect, that a mother provides a significant complement of her offsprings cuticular hydrocarbons. Further research will be needed to determine whether provisioning hydrocarbons to eggs is a general strategy among insects and other arthropods or if this strategy is limited to taxa where eggs and early instars are susceptible to desiccation.