Chemical Attraction of Gall Midge Pollinators (Cecidomyiidae: Cecidomyiinae) to Anthurium acutangulum (Araceae)

Abstract

Flowering plants often use chemical signals to attract their pollinators, and compounds that elicit attraction are known for several groups of pollinators. For other pollinators such as gall midges, however, compounds responsible for their attraction to flowers are largely unknown. Here, we describe the pollination biology of Anthurium acutangulum, a Neotropical aroid species found to be attractive to gall midges. We collected and analyzed its floral scent by dynamic headspace collections and gas chromatography coupled to mass spectrometry, and identified compounds responsible for pollinator attraction. The inflorescences were almost exclusively visited by gall midges (females; Cecidomyiidae: Cecidomyiinae) and released a strong scent reminiscent of freshly cut cucumber, mainly (5S,7S)-trans-conophthorin, (E2,Z6)-2,6-nonadienal, and cis-conophthorin. Behavioral assays with the two most abundant compounds identified (E2,Z6)-2,6-nonadienal as being highly attractive to the female gall midge pollinators, whereas (5S,7S)-trans-conophthorin was not attractive. Overall, we introduce a new specialized gall midge pollination system and identify the chemical mediating communication between the pollinators and their host plants.

Pollination of Oberonia japonica (Orchidaceae) by gall midges (Cecidomyiidae)

“…While Oberonia is a diverse genus of 150-300 species, there are notable similarities in morphology among them, with minute flowers in monochromatic or sometimes dichromatic colors ranging from light to dark green to yellow, orange, or red. These colors resemble those of other gall midge-pollinated flowers found in different plant families (Arnold et al, 2019;Bogner, 2011;Etl et al, 2022;Gan et al, 2022;Gardner et al, 2018;Kawakita et al, 2022;Luo et al, 2010;Thien et al, 2003;Vislobokov et al, 2014), suggesting that gall midge pollination could be widespread across the genus. Because gall midges are small and are often active at night (Gan et al, 2022), orchid pollination by gall midges may go unnoticed in other genera.…”

“…There is therefore some potential that the inflorescence of O. japonica mimics lek formation by male gall midges. Floral scent may also be involved, as we were able to detect a weak but distinct smell, and floral scent has been shown to attract gall midges to other plants (Etl et al, 2022). Additional study at different locations to confirm specificity of the gall midge species, as well as analysis of floral scent that might attract female gall midges, is necessary to fully understand the mechanism by which gall midges are attracted to Oberonia flowers.…”

“…Gall midge pollination is a rare pollination system currently found in 43 species belonging to 10 plant families (Bogner, 2011; Etl et al, 2022; Gan et al, 2022; Kawakita et al, 2022; Matsumoto et al, 2022). Some known examples of gall midge pollination involve brood‐site rewards (Kawakita et al, 2022; Luo et al, 2010), but brood‐site pollination is unlikely in Oberonia because no oviposition behavior was observed, and no larvae emerged from sampled inflorescences.…”

Chemistry, biosynthesis and biology of floral volatiles: roles in pollination and other functions

“…Since 2010, a large number of studies identied compounds attractive to ower visitors. The behaviorally active compounds were main compounds of the released scent in some pollination systems, e.g., 365 while they were only minor or even trace compounds in others. We now have a much better understanding how plants communicate with beetle, lepidopteran, bee and y pollinators, and the rst attractants were also identied for less common pollinators, such as rodents, shrews and true bugs.…”