Advertisement of unreceptivity - Perfume modifications of mason bee females (Osmia bicornis and O. cornuta) and a non-existing antiaphrodisiac

Romance in peril: A common pesticide impairs mating behaviours and male fertility of solitary bees (Osmiabicornis)

Mating behaviour and fertility are strong selective forces, driving the reproductive trends of animals. Mating disorders may therefore contribute to the recent decline in insect and pollinators health worldwide. While the impact of pesticides on pollinators is widely considered as a driving factor for reducing pollinators health, their effect on mating behaviour and male fertility remains widely overlooked. Here, we assessed the effects of field-realistic exposure to a common pesticide used as a neonicotinoid substitute worldwide, sulfoxaflor, on the behaviour and male physiology of the solitary bee, Osmia bicornis. We measured a variety of parameters focusing on behaviours occurring before, and during mating, as well as sperm quantity. For the first time, we demonstrate that short-term chronic, field-realistic exposure to a common pesticide reduced pre-copulatory display (-36 %) and sounds (-27 %), increased the number of copulations (+110 %) and the mating duration (+166 %), while finally reducing sperm quantity (-25 %) and mating success (-43 %). Our research raises considerable concern on the impact of field-realistic, low sublethal pesticide levels on the fertility and reproductive success of pollinators. Assessing the impact of pesticides on fitness parameters and implementing more sustainable agricultural solutions would allow mitigating the ongoing threat of pesticide pollution on wild insect populations and the broader environment.

Fungicide ingestion reduces net energy gain and microbiome diversity of the solitary mason bee

Fungicides are frequently used during tree fruit bloom and can threaten insect pollinators. However, little is known about how non-honey bee pollinators such as the solitary bee, Osmia cornifrons, respond to contact and systemic fungicides commonly used in apple production during bloom. This knowledge gap limits regulatory decisions that determine safe concentrations and timing for fungicide spraying. We evaluated the effects of two contact fungicides (captan and mancozeb) and four translaminar/plant systemic fungicides (cyprodinil, myclobutanil, penthiopyrad, and trifloxystrobin) on larval weight gain, survival, sex ratio, and bacterial diversity. This assessment was carried out using chronic oral ingestion bioassays where pollen provisions were treated with three doses based on the currently recommended field use dose (1X), half dose (0.5X), and low dose (0.1X). Mancozeb and penthiopyrad significantly reduced larval weight and survival at all doses. We then sequenced the 16S gene to characterize the larvae bacteriome of mancozeb, the fungicide that caused the highest mortality. We found that larvae fed on mancozeb-treated pollen carried significantly lower bacterial diversity and abundance. Our laboratory results suggest that some of these fungicides can be particularly harmful to the health of O. cornifrons when sprayed during bloom. This information is relevant for future management decisions about the sustainable use of fruit tree crop protection products and informing regulatory processes that aim to protect pollinators.

Biology, Genetic Diversity, and Conservation of Wild Bees in Tree Fruit Orchards

Different species of bees provide essential ecosystem services by pollinating various agricultural crops, including tree fruits. Many fruits and nuts depend on insect pollination, primarily by wild and managed bees. In different geographical regions where orchard crops are grown, fruit growers rely on wild bees in the farmscape and use orchard bees as alternative pollinators. Orchard crops such as apples, pears, plums, apricots, etc., are mass-flowering crops and attract many different bee species during their bloom period. Many bee species found in orchards emerge from overwintering as the fruit trees start flowering in spring, and the active duration of these bees aligns very closely with the blooming time of fruit trees. In addition, most of the bees in orchards are short-range foragers and tend to stay close to the fruit crops. However, the importance of orchard bee communities is not well understood, and many challenges in maintaining their populations remain. This comprehensive review paper summarizes the different types of bees commonly found in tree fruit orchards in the fruit-growing regions of the United States, their bio-ecology, and genetic diversity. Additionally, recommendations for the management of orchard bees, different strategies for protecting them from multiple stressors, and providing suitable on-farm nesting and floral resource habitats for propagation and conservation are discussed.

Individual Scent-Marks of Nest Entrances in the Solitary Bee, Osmia cornuta (Hymenoptera: Apoidea)

The ability to recognize the own nest is a basic skill in nest constructing solitary bees. Osmia cornuta females use a dual mechanism of visual orientation to approach a nest and olfactory verification of the tube when entering it. Occupied tubular cavities were steadily marked by the resident female. Nest marking substances originate from Dufour's gland and cuticle, enriched by external volatiles. Scent tags were dominated by alkanes and alkenes in a species-specific mixture enriched by small amounts of fatty acid esters, alcohols, and aldehydes. The individual nest tags are sufficiently variable but do not match perfectly with the nesting female. Furthermore, tags are not consistent over time, although females continue in marking. Besides the correct position of the entrance in space, bees have to learn also the bouquet of the used cavity and update their internal template at each visit to recognize their own nest by its actual smell. Due to the dominance of the species-specific hydrocarbon pattern, nest marks may function not only as an occupied sign but may also provide information on the species affiliation and constitution of the nest owner.

Changes in chemical cues of Melissococcus plutonius infected honey bee larvae

European foulbrood (EFB), caused by Melissococcus plutonius, is a globally distributed bacterial brood disease affecting Apis mellifera larvae. There is some evidence, even if under debate, that spreading of the disease within the colony is prevented by worker bees performing hygienic behaviour, including detection and removal of infected larvae. Olfactory cues (brood pheromones, signature mixtures, diagnostic substances) emitted by infected individuals may play a central role for hygienic bees to initiate the disease-specific behaviour. However, the mechanisms of cue detection and brood removal, causing hygienic behaviour in EFB affected colonies, are poorly understood. Here, coupled gas chromatography-mass spectrometry (GC–MS) was used to detect disease-specific substances, changes in cuticular hydrocarbon (CHC) profiles, and brood ester pheromones (BEPs) of honey bee larvae artificially infected with M. plutonius. Although no diagnostic substances were found in significant quantities, discriminant analysis revealed specific differences in CHC and BEP profiles of infected and healthy larvae. β-Ocimene, a volatile brood pheromone related to starvation and hygienic behaviour, was present in all larvae with highest quantities in healthy young larvae; whereas oleic acid, a non-volatile necromone, was present only in old infected larvae. Furthermore, γ-octalactone (newly discovered in A. mellifera in this study) was detectable in trace amounts only in infected larvae. We propose that the deviation from the olfactory profile of healthy brood is supposed to trigger hygienic behaviour in worker bees. To confirm the relevance of change in the chemical bouquet (CHCs, BEPs, γ-octalactone, etc.), a field colony bioassay is needed, using healthy brood and hygienic bees to determine if bouquet changes elicit hygienic behaviour.

Mating status and the evolution of eusociality: Oogenesis is independent of mating status in the solitary bee Osmia bicornis

The fundamental trait underlying eusociality is the reproductive division of labour. In honeybees (Apis mellifera), queens lay eggs while workers forage, defend and care for brood. The division of labour is maintained by pheromones including queen mandibular pheromone (QMP) produced by the queen. QMP constrains reproduction in adult honeybee workers, but in the absence of their queen workers can activate their ovaries and, although they cannot mate, they lay haploid male eggs. The reproductive ground plan hypothesis suggests that reproductive constraint may have evolved by co-opting mechanisms of reproductive control in solitary ancestors. In many insects mating is required to activate or accelerate oogenesis. Here, we use the solitary bee Osmia bicornis (Megachilidae) to test whether reproductive constraint evolved from ancestral control of reproduction by mating status. We present a structural study of the O. bicornis ovary, and compare key stages of oogenesis with honeybee workers. Importantly, we show that mating does not affect any aspect of the reproductive physiology of O. bicornis. We therefore conclude that mechanisms governing reproductive constraint in honeybees were unlikely to have been co-opted from mechanisms pertaining to mating status.