Ayrton Vollet-Neto

The origin and evolution of queen and fertility signals in Corbiculate bees.

BackgroundIn social Hymenoptera (ants, bees and wasps), various chemical compounds present on the cuticle have been shown to act as fertility signals. In addition, specific queen-characteristic hydrocarbons have been implicated as sterility-inducing queen signals in ants, wasps and bumblebees. In Corbiculate bees, however, the chemical nature of queen-characteristic and fertility-linked compounds appears to be more diverse than in ants and wasps. Moreover, it remains unknown how queen signals evolved across this group and how they might have been co-opted from fertility signals in solitary ancestors.ResultsHere, we perform a phylogenetic analysis of fertility-linked compounds across 16 species of solitary and eusocial bee species, comprising both literature data as well as new primary data from a key solitary outgroup species, the oil-collecting bee Centris analis, and the highly eusocial stingless bee Scaptotrigona depilis. Our results demonstrate the presence of fertility-linked compounds belonging to 12 different chemical classes. In addition, we find that some classes of compounds (linear and branched alkanes, alkenes, esters and fatty acids) were already present as fertility-linked signals in the solitary ancestors of Corbiculate bees, while others appear to be specific to certain species.ConclusionOverall, our results suggest that queen signals in Corbiculate bees are likely derived from ancestral fertility-linked compounds present in solitary bees that lacked reproductive castes. These original fertility-linked cues or signals could have been produced either as a by-product of ovarian activation or could have served other communicative purposes, such as in mate recognition or the regulation of egg-laying.

The Role of Useful Microorganisms to Stingless Bees and Stingless Beekeeping

Bacteria, molds, and yeasts associated with bees have been studied for a long period. Although they seem to play an important role for bee nutrition and protection against harmful microorganisms, few studies have focused on their function and this subject is still very controversial. Although stingless bees (Apidae: Meliponini) share many similarities with Apis mellifera, this diverse group still conceals many particularities that have not been explored at all. In this chapter, we discuss the role of non-pathogenic microorganisms from stingless bee colonies and we focus on their applicability to stingless bee keeping. Our aim is to stimulate studies on functional aspects of microorganisms from stingless bees and their products where upon microorganisms are involved.

Repeated evolution of soldier sub-castes suggests parasitism drives social complexity in stingless bees

The differentiation of workers into morphological castes represents an important evolutionary innovation that is thought to improve division of labor in insect societies. Given the potential benefits of task-related worker differentiation, it is puzzling that physical worker castes, such as soldiers, are extremely rare in social bees and absent in wasps. Following the recent discovery of soldiers in a stingless bee, we studied the occurrence of worker differentiation in 28 stingless bee species from Brazil and found that several species have specialized soldiers for colony defence. Our results reveal that worker differentiation evolved repeatedly during the last ~ 25 million years and coincided with the emergence of parasitic robber bees, a major threat to many stingless bee species. Furthermore, our data suggest that these robbers are a driving force behind the evolution of worker differentiation as targets of robber bees are four times more likely to have nest guards of increased size than non-targets. These findings reveal unexpected diversity in the social organization of stingless bees.Although common in ants and termites, worker differentiation into physical castes is rare in social bees and unknown in wasps. Here, Grüter and colleagues find a guard caste in ten species of stingless bees and show that the evolution of the guard caste is associated with parasitization by robber bees.

Soldiers in a Stingless Bee

The differentiation of workers into morphological subcastes (e.g., soldiers) represents an important evolutionary transition and is thought to improve division of labor in social insects. Soldiers occur in many ant and termite species, where they make up a small proportion of the workforce. A common assumption of worker caste evolution is that soldiers are behavioral specialists. Here, we report the first test of the “rare specialist” hypothesis in a eusocial bee. Colonies of the stingless bee Tetragonisca angustula are defended by a small group of morphologically differentiated soldiers. Contrary to the rare specialist hypothesis, we found that soldiers worked more (+34%–41%) and performed a greater variety of tasks (+23%–34%) than other workers, particularly early in life. Our results suggest a “rare elite” function of soldiers in T. angustula, that is, that they perform a disproportionately large amount of the work. Division of labor was based on a combination of temporal and physical castes, but soldiers transitioned faster from one task to the next. We discuss why the rare specialist assumption might not hold in species with a moderate degree of worker differentiation.

Consumption of the neonicotinoid thiamethoxam during the larval stage affects the survival and development of the stingless bee, Scaptotrigona aff. depilis

In Brazil, where the use of neonicotinoids is allowed in bee-attracting flowering crops, we investigated whether thiamethoxam intake during the larval stage of the native bee species Scaptotrigona aff. depilis affects the survival and development by exposing larvae to contaminated food. Our results indicated that the larvae exposed to the dose at a field-realistic level and to the doses ranging around it had their survival rates significantly impaired. At the highest doses, we observed larvae and pupae with shorter and longer development times, respectively, and the formation of smaller and asymmetric specimens. Evidently, we need to consider that thiamethoxam reaches the pollen and nectar at residual levels, and that they are processed by nurse bees before destined for offspring. Nevertheless, our findings suggest a warning, since the individuals had their biological parameters affected by thiamethoxam, when exposed to doses at field-realistic levels.

Intraspecific worker parasitism in the common wasp, Vespula vulgaris

Insect societies display a remarkable level of cooperation, but their colonies also represent a valuable resource that can be taken advantage of by genetically unrelated individuals. Indeed, several recent studies have documented cases of intraspecific reproductive parasitism, whereby workers penetrate and lay eggs in unrelated colonies in order to have their brood raised by the host workers. Previously, it has been predicted that queenless colonies should be a prime target of such intraspecific worker parasitism, as in such colonies the parasite workers would be able to reproduce without interference from either the queen or other workers. So far, this prediction has been supported with data from the honeybee, but evidence from other social insect groups is currently lacking. Here we present the first such test in the common wasp, Vespula vulgaris. In particular, workers from queenright colonies left the natal nest at a higher rate than those from queenless colonies. However, contrary to our predictions, drifter workers targeted queenless and queenright colonies equally. Chemical data suggest that this lack of discrimination may be linked to recognition constraints and the lack of volatile signals that reliably indicate the presence or absence of the queen. In addition, in queenright colonies, drifters activated their ovaries at a rate that was ca. five times higher than the natal workers. Overall, our results suggest that also in wasps, workers can gain inclusive fitness by drifting to unrelated nests, even if the chances of successfully reproducing there may be very slim.

Brood production increases when artificial heating is provided to colonies of stingless bees

Summary Although stingless bees are capable of maintaining their nest temperature within certain limits, brood production of several species declines or even completely stops during periods of low ambient temperature. In the present study, we investigated whether the brood production of the meliponine species Nannotrigona testaceicornis can be artificially increased through heating the colonies during the cold season. For this, we monitored the rate of brood cell production of seven hives in intervals of 24 hours under two different experimental conditions: 1. without; and 2. with heating. Each treatment (first with and subsequently without heating) lasted for nine consecutive days. The ambient temperature (TA) during both experimental periods was very similar (TAWITH = 16.1°C; TAWITHOUT = 16.3°C). On average, the colonies built 3.6 brood cells per day without and 15.8 brood cells per day with artificial heating (Wilcoxon Rank Sum test: T = 10, Z = 4, P < 0.001). In both treatments, the rate of brood cell production increased with increasing environmental temperature (Spearman Rank Correlation: RWITH = 0.71, P = 0.02; RWITHOUT = 0.66, P = 0.05). We concluded that artificial heating during cold periods increased the brood cell production in N. testaceicornis. Our results indicate that the use of heaters for stingless bee hives during periods of low ambient temperature may be helpful for stingless beekeeping.

Stingless Bee Larvae Require Fungal Steroid to Pupate

The larval stage of the stingless bee Scaptotrigona depilis must consume a specific brood cell fungus in order to continue development. Here we show that this fungus is a member of the genus Zygosaccharomyces and provides essential steroid precursors to the developing bee. Insect pupation requires ecdysteroid hormones, and as insects cannot synthesize sterols de novo, they must obtain steroids in their diet. Larval in vitro culturing assays demonstrated that consuming ergosterol recapitulates the developmental effects on S. depilis as ingestion of Zygosaccharomyces sp. cells. Thus, we determined the molecular underpinning of this intimate mutualistic symbiosis. Phylogenetic analyses showed that similar cases of bee-Zygosaccharomyces symbiosis may exist. This unprecedented case of bee-fungus symbiosis driven by steroid requirement brings new perspectives regarding pollinator-microbiota interaction and preservation.

Recent advances in reproductive biology of stingless bees

The reproductive biology of stingless bees is poorly understood, especially when compared to other groups of social bees with great ecological and economic importance. However, research on this topic has grown over the past few years, mostly driven by technological advances in molecular biology. Here, we aimed to review several recent developments in the research of stingless bee reproduction, including the mating systems of stingless bees, reproductive strategies of queens, inbreeding and diploid male production, as well as conflicts over male production. We also briefly explore topics that have not substantially advanced, highlighting the gaps that need to be further investigated. Understanding the reproductive biology of stingless bees can aid conservation efforts for these important pollinators and improve management practices that promote their sustainable economic use.