Pollination of orchids
Notably, the topic has garnered significant scientific interest over time, including the attention of Charles Darwin, who is recognized for his contributions to the theory of evolution by natural selection.
Approximately 97% of orchid species rely on pollinator for the transfer of pollen from one plant to the pistils of another, which is essential for fertilization and seed formation.
[3] The pollen of orchids is organized into compact masses known as pollinia (singular: "pollinium"), preventing dispersal by wind and necessitating the presence of pollinators for sexual reproduction.
[4][5][3] The phenomenon of zoophily in orchids requires that pollinating animals frequently visit the flowers and remain long enough to contact both the anthers and stigma.
[4] Throughout the evolution of angiosperms, there has been significant differentiation in the means of attraction and flower morphology, allowing a broader range of animals to participate in pollination.
[7] Many orchid species provide various rewards to pollinators, including nectar, food hairs, oils, and other compounds such as waxes, resins, and fragrances.
Over time, this specialization on a single type of pollinator has led to increased morphological and structural adaptations in orchid flowers, aimed at attracting specific insect species.
Based on this reasoning, Darwin suggested that the pollinator of Angraecum sesquipedale would need to have a proboscis longer than 30 cm, an idea that seemed implausible to contemporary biologists.
[3] Many orchids, including Angraecum sesquipedale, are pollinated by nocturnal butterflies and, as a result, tend to have light-colored or nearly white flowers that emit fragrance in the evening or night.
[12] In contrast, some orchid genera have evolved to be pollinated by diurnal butterflies, exhibiting bright colors and providing nectar as a reward.
Notable genera that provide oil rewards include Disperis, Pterygodium, Corycium, Ceratandra, Evotella, Satyrium, and Pachites.
[13] These flowers typically emit scents reminiscent of decaying organic materials, excrement, or carrion, which attract flies seeking food or suitable sites for egg deposition.
[8] Various floral parts produce putrescent or carrion-like odors and often incorporate traps to retain the pollinators, alongside appendages and colors that may mimic flesh or other aspects of rotting matter.
Using the long, dense hairs on its front legs, the bee gathers the aromatic substances, which are typically liquid but can also be found in crystalline form.
[20] Orchids, like many plants, attract specific groups of male euglossine bees by producing species-specific scent mixtures, which likely act as reproductive isolation mechanisms.
Some orchids exhibit morphological adaptations that ensure pollinia are only released upon visitation by particular bee species, depending on their size and behavior.
Methyl eugenol serves as a sex pheromone precursor for several quarantine pest species of Bactrocera, including the oriental fruit fly (B. dorsalis), B. carambolae, B. occipitalis, and B. umbrosa.
Similarly, raspberry ketone and zingerone function as sex pheromone components for male fruit flies like Zeugodacus caudatus, Z. cucurbitae, and Z.
[28][29] The ability to attract pollinators without offering rewards has evolved independently across several angiosperm lineages, although it typically occurs in only a few species within each family.
[35] Feeding deception commonly manifests as a general resemblance to rewarding species, with orchids featuring large, brightly colored flowers that exploit pollinators' innate preferences for such floral characteristics.
The butterfly Agraulis vanillae, which typically visits Asclepias curassavica to collect nectar in exchange for pollen transport, is frequently drawn to the mimetic flowers of Epidendrum ibaguense.
[37] Certain orchids have evolved deceptive flowers that mimic the shape, hairiness, and scent of female wasps or bees to attract male pollinators.
[38] The phenomenon of pollination by pseudocopulation was first documented by A. Pouyanne and H. Correvon in 1916 and 1917 while studying the relationship between the orchid Ophrys speculum and the scoliidae wasp Campsoscolia ciliata in Algeria.
[note 3] Following this, Australian biologist Edith Coleman published numerous papers on the pollination of orchids from the genus Cryptostylis by males of the ichneumonoidea wasp Lissopimpla excelsa.
[41][42][43] Several genera of terrestrial orchids employ this pseudocopulation mechanism, including Ophrys, Cryptostylis, Drakaea, Caladenia,[44] Chiloglottis,[45] Geoblasta,[46] Arthrochilus, Calochilus,[47] Leporella,[48] and Spiculaea.
Chemical and electrophysiological comparisons have been made between the volatile compounds emitted by Ophrys iricolor and the female pheromones of its pollinator, Andrena morio.
