Sidnei Mateus

Queen signals in a stingless bee: suppression of worker ovary activation and spatial distribution of active compounds

In most species of social insect the queen signals her presence to her workers via pheromones. Worker responses to queen pheromones include retinue formation around the queen, inhibition of queen cell production and suppression of worker ovary activation. Here we show that the queen signal of the Brazilian stingless bee Friesella schrottkyi is a mixture of cuticular hydrocarbons. Stingless bees are therefore similar to ants, wasps and bumble bees, but differ from honey bees in which the queens signal mostly comprises volatile compounds originating from the mandibular glands. This shows that cuticular hydrocarbons have independently evolved as the queens signal across multiple taxa, and that the honey bees are exceptional. We also report the distribution of four active queen-signal compounds by Matrix-assisted laser desorption/ionization (MALDI) imaging. The results indicate a relationship between the behavior of workers towards the queen and the likely site of secretion of the queens pheromones.

Nestmate recognition in a neotropical polygynous wasp

Abstract.In social insects, nestmate recognition systems can be dynamic and modulated in response to various kinds of genetic and environmental cues. For example, multiple-queen colonies can possess weak recognition abilities relative to single-queen colonies, due to broader exposure to heritable and environmentally derived nestmate recognition cues.We conducted field experiments to examine nestmate recognition ability in a neotropical polygynous wasp, Polybia paulista. Despite the fact that the effective queen number in P. paulista is the highest ever recorded in polygynous wasps, this species exhibits a well functioning nestmate recognition system, which allows colony entry only to nestmate individuals. Similar to other social Hymenoptera, young wasps express colony specific chemical signatures within several days after emergence. This is the first study to show that the polygynous epiponine wasp is able to distinguish nestmates from non-nestmates.

Stable relatedness structure of the large-colony swarm-founding wasp Polybia paulista

In social-insect colonies, cooperation among nestmates is generally stabilized by their high genetic similarity. Thus, fitness gained through cooperation drops quickly as the number of reproductive females (queens) increases. In this respect, wasps of the tribe Epiponini have attracted special attention, because the colonies have tens, or even hundreds of queens. It has been empirically or genetically confirmed that relatedness within nestmates can be elevated by a mechanism known as cyclical monogyny, under which new queens are produced only after the number of old queens is reduced to one. Another likely factor that can increase relatedness within nestmates under polygyny is comb partitioning by queens. If queens concentrate their egg laying on one or a subset of the available combs, then workers may be able to rear closer relatives by focusing their work on the comb where they emerged. Using microsatellite markers, we tested the hypotheses of cyclical monogyny and comb partitioning by queens increasing relatedness within nestmates under polygyny in the large-colony epiponine wasp, Polybia paulista. There were no significant differences between relatedness within combs and between combs, and thus we ruled out the possibility that each queen partitions reproduction between combs. However, as cyclical monogyny predicts, a lower effective number of queens contributed to queen production than to worker production. Cyclical monogyny explained well the observed smaller effective number of queens for new queens than that for workers, but failed to explain the stable relatedness values throughout colony cycles.

Parasitism affects worker size in the Neotropical swarm-founding social wasp, Polybia paulista (Hymenoptera, Vespidae)

SummaryWe discovered two kinds of parasites, i.e., a strepsipteran, possibly Xenos myrapetrus (Trois) and an undescribed gregarine in the Neotropical swarm-founding paper wasp, Polybia paulista (Ihering). Although proportions of workers that were infected by these parasites varied greatly among colonies analyzed, prevalence of infected workers was recognized. Five external characters were measured and compared among uninfected workers, stylopized (i.e., infected by Strepsiptera) workers and workers that were infected by gregarines. Uninfected workers were significantly larger than stylopized workers, while smaller than workers that were infected by gregarines. Nutrients of stylopized workers may be plundered during their growth period, and consequently their body size may be reduced. However, the gregarines may manipulate host larvae to solicit more food from adults or increase development time of larvae longer, and therefore produce more parasites from a larger host.

Food profitability affects intranidal recruitment behaviour in the stingless bee Nannotrigona testaceicornis

Does the food’s sugar concentration affect recruitment behaviour in the stingless bee Nannotrigona testaceicornis? We recorded intranidal forager behaviour while offering sugar water of constant, increasing, or decreasing concentrations. Running speed was not correlated with sugar concentration but the jostling contacts/sec were. Food profitability also affected the recruiter’s thorax vibrations: Pulse duration and duty cycle followed both concentration increases and decreases. Sugar concentration also influenced the number of recruited bees. In comparison to the phylogenetically closely related Scaptotrigona, Nannotrigona’s intranidal recruitment behaviour showed a more elaborate association with food profitability. This is likely to reflect differences in ecology and foraging strategies as Nannotrigona — in contrast to Scaptotrigona — does not lay scent trails to guide recruits to a food source.ZusammenfassungIn der vorliegenden Studie wurde das Rekrutierungsverhalten der stachellosen Biene Nannotrigona testaceicornis untersucht. Phylogenetisch ist diese Art nahe mit der Gattung Scaptotrigona verwandt, jedoch unterscheidet sie sich im Verhalten während der Futtersuche: Nannotrigona legt im Gegensatz zu Scaptotrigona keine Duftpfade als Wegweiser zur Futterquelle. Obgleich mit Nannotrigona nicht nahe verwandt, legen auch Bienen der Gattung Melipona keinen Duftpfad bei der Nahrungssuche an. Frühere Arbeiten (z.B. Nieh et al., 2003; Hrncir et al., 2004a,b; Schmidt et al., 2006b) beschrieben das Rekrutierungsverhalten von Melipona und Scaptotrigona innerhalb des Nestes. Dabei zeigte sich, dass Melipona (kein Duftpfad) auf Veränderungen von Futterqualität mit einer Veränderung des Verhaltens (Thoraxvibrationen) innerhalb des Nestes reagiert, während Scaptotrigona (Duftpfad) nach Veränderungen der Futterqualität im Nest ihr Verhalten kaum änderte. Die vorliegende Studie fragt nach dem Einfluss der Futterqualität auf das intranidale Rekrutierungsverhalten einer Art, die trotz naher taxonomischer Verwandtschaft mit Duftpfad-Bienen keinen Duftpfad auslegt. Im Experiment wurde Nannotrigona 35 m vom Nest entfernt eine Futterquelle geboten, deren Zuckerwasserkonzentration konstant gehalten (Kontrollversuche) oder erhöht bzw. erniedrigt wurde. Zugleich wurde innerhalb des Nestes gemessen, mit welcher Geschwindigkeit die Sammelbienen im Nest laufen, wie oft sie ihre Nestgenossinnen pro Sekunde rempeln und welche Thoraxvibrationen sie abgeben. Die Kontrollversuche zeigten, dass die Rempelaktivität gegensätzlich zur Laufgeschwindigkeit bei konstanter Zuckerkonzentration über die Versuchszeit konstant blieb. Mit veränderten Zuckerkonzentrationen änderten die Bienen ihre Rempelaktivität: Während deren Intensität mit zunehmendem Zuckergehalt ebenfalls zunahm, verminderte sie sich infolge abnehmender Zuckerkonzentration. Ebenso hingen die Eigenschaften der Thoraxvibrationen stark von der Konzentration des Futterwassers ab: Bei ansteigender Zuckerkonzentration erhöhten die Bienen die Pulslänge der Vibrationen und auch der Duty Cycle (Aktivitätsmaß) stieg signifikant an. Bei stündlich abnehmender Zuckerkonzentration wurden die Vibrationspulse signifikant kürzer, die Pausen zwischen den Pulsen länger und damit auch der Duty Cycle kleiner. Diese Befunde erfüllen die Erwartungen, dass Bienen ohne Duftpfad (Nannotrigona) eine raffiniertere Kommunikation innerhalb des Nestes anwenden als nahe verwandte Bienen, die Duftpfade außerhalb des Nestes als Wegweiser nutzen.

Chemical identity of recently emerged workers, males, and queens in the stingless bee Melipona marginata

Epicuticular hydrocarbons are involved in several behavioral processes in social insects including recognition of nestmates, castes, and sex. The aim of the present study was to characterize and to verify differences in the chemical profiles of 1-day recently emerged workers, males, and queens in colonies of the stingless bee Melipona marginata. Gas chromatography–mass spectrometry and multivariate analyses of bee samples from three colonies clearly separated cuticular hydrocarbon profiles of males, queens, and workers. The results showed that cuticular hydrocarbon profiles were comprised of alkanes, alkenes, and methyl alkanes that varied quantitatively and qualitatively according to the castes and sex. Different from previous studies, our investigation also demonstrated that males and queens presented higher similarity in their epicuticular hydrocarbons than to workers.

Nest thermoregulation in Polybia scutellaris (White) (Hymenoptera: Vespidae)

Polybia scutellaris (White) builds large nests characterized by numerous spiny projections on the surface. In order to determine whether or not the nest temperature is maintained because of homeothermic conditions of the nest individuals or otherwise, we investigated the thermal conditions within the nests built by P. scutellaris. We measured the temperature within active and abandoned nests. The temperature in the active nest was almost stable at 27°C during data collection, whereas the temperature in the abandoned nest varied with changes in ambient temperature. These results suggest that nest temperature was maintained by the thermogenesis of the individuals of the colony. This is the first report of nest incubation caused by thermogenesis of species of Polybia wasps.

Diel changes of temperature in the nests of two Polybia species, P. paulista and P. occidentalis (Hymenoptera, Vespidae) in the subtropical climate

Temperatures in two mature Polybia nests were measured to study the thermal conditions of nests. Temperatures in a Polybia paulista nest were measured when it had adult wasps (trial 1) and after the adult wasps were removed (trial 2), and temperatures in a P. occidentalis nest were measured when inhabited by adult wasps (trial 3). In each trial, C–C thermocouples were set at four points in the nest and at two points outside to discover the ambient and substratum temperatures. In trial 1, nest temperatures basically followed the ambient temperature, but during the day the nest temperatures were lower than the ambient temperature and this relationship was reversed during the night. The temperature fluctuation of the inner substratum points was smaller than that of the outer points. The trend of trial 2 was closely similar to that of trial 1, showing a virtual lack of thermal effects from the presence of adult wasps. In trial 3, the changing pattern in the P. occidentalis nest showed a trend similar to that in the P. paulista nest, but the inside temperatures rose quickly when the nest received direct sunlight in the morning. From these results, thermal characteristics in the Polybia nests are discussed in relation to the nest architecture and their geographical distribution.

Mixed colonies of two species of congeneric stingless bees (Hymenoptera: Apinae, Meliponini) display environmentally‐acquired and endogenously‐produced recognition signals

Nestmate recognition is fundamental for the maintenance of social organization in insect nests. It is becoming well recognized that cuticle hydrocarbons mediate the recognition process, although the origin of recognition cues in stingless bees remains poorly explored. The present study investigates the effects of endogenously‐produced and environmentally‐acquired components in cuticular hydrocarbons in stingless bees. The tests are conducted using colonies of Plebeia droryana Friese and Plebeia remota Holmberg. Recognition tests are performed with four different groups: conspecific nestmates, conspecific non‐nestmates, heterospecifics and conspecific, genetically‐related individuals that emerge in a heterospecific nest. This last group is produced by introducing brood cells of P. droryana into a P. remota colony, and the resulting adult bees are tested for acceptance 10 days after emergence. For all groups, 15 individuals are sampled for chemical analysis. The results show the acceptance of all conspecific nestmates, and the rejection of almost every conspecific non‐nestmate and every heterospecific bee. Genetically‐related individuals emerging from heterospecific nests present intermediate rejection (66.7% rejection). Chemical analysis shows that P. droryana individuals emerging in a P. remota nest have small amounts of alkene and diene isomers found in P. remota cuticle that are not found in workers from the natal nest. The data clearly show that the majority of the compounds present in P. droryana cuticle are endogenously produced, although a few unsaturated compounds are acquired from the environment, increasing the chemical differences and, consequently, the rejection percentages.

Morphological Caste Differences in Three Species of the Neotropical Genus Clypearia (Hymenoptera: Polistinae: Epiponini)

Clypearia is a rare genus of swarm-founding Neotropical wasp whose biology is very little known. Morphological castes differences, condition of ovaries, relative age, and color pattern differences were analyzed in three species of Clypearia. Physiological differences and low morphometric differentiation between queens and workers were present in all species studied, indicating that these species are characterized by “physiological caste only”. We suggest that caste determination in the three Clypearia species studied is postimaginal.