Nectar Uptake of a Long-Proboscid Prosoeca Fly (Nemestrinidae)—Proboscis Morphology and Flower Shape

Abstract

Several Prosoeca (Nemestinidae) species use a greatly elongated proboscis to drink nectar from long-tubed flowers. We studied morphological adaptations for nectar uptake of Prosoecamarinusi that were endemic to the Northern Cape of South Africa. Our study site was a small isolated area of semi-natural habitat, where the long-tubed flowers of Babiana vanzijliae (Iridaceae) were the only nectar source of P. marinusi, and these flies were the only insects with matching proboscis. On average, the proboscis measured 32.63 ± 2.93 mm in length and less than 0.5 mm in diameter. The short labella at the tip are equipped with pseudotracheae that open at the apical margin, indicating that nectar is extracted out of the floral tube with closed labella. To quantify the available nectar resources, measurements of the nectar volume were taken before the flies were active and after observed flower visits. On average, an individual fly took up approximately 1 µl of nectar per flower visit. The measured nectar quantities and the flower geometry allowed estimations of the nectar heights and predictions of necessary proboscis lengths to access nectar in a range of flower tube lengths.

Pollination syndrome accurately predicts pollination by tangle‐veined flies (Nemestrinidae: Prosoeca s.s.) across multiple plant families

“…The underside of the disc is traversed by a series of channels (pseudo-tracheae), which presumably help to sponge up the nectar. The pseudo-tracheal system might also distribute saliva onto the surface when feeding on concentrated nectar (Krenn et al 2005(Krenn et al , 2021). The sponging mode of feeding, as performed by a short proboscis, represents the ancestral method of fluid uptake in Diptera (Krenn et al 2021).…”

“…The pseudo-tracheal system might also distribute saliva onto the surface when feeding on concentrated nectar (Krenn et al 2005(Krenn et al , 2021). The sponging mode of feeding, as performed by a short proboscis, represents the ancestral method of fluid uptake in Diptera (Krenn et al 2021). In contrast, the long-proboscid Prosoeca species, which extract larger volumes of more dilute nectar from narrow floral tubes, keep their elongated labella closed when feeding (Appendix S6) (Karolyi et al 2012).…”

“…The pseudo‐tracheal system might also distribute saliva onto the surface when feeding on concentrated nectar (Krenn et al . 2005 , 2021 ). The sponging mode of feeding, as performed by a short proboscis, represents the ancestral method of fluid uptake in Diptera (Krenn et al .…”

Evolutionary functional morphology of the proboscis and feeding apparatus of hawk moths (Sphingidae: Lepidoptera)

“…A similar morphology has been described in Hesperiidae as well as long‐proboscid Riodinidae (Bauder et al, 2013 ; Krenn & Bauder, 2017 ) and seems to be a feature displayed by all nectar‐consuming Lepidoptera that are adapted to particularly long nectar spurs (Bauder & Karolyi, 2019 ). Some other nectar‐feeding insects, i.e., nemestrinid or tabanid flies, display similar morphological adaptations comprising a long, slender proboscis and a smooth apical region with remarkably few and short sensilla (Karolyi et al, 2012 , 2014 ; Krenn et al, 2021 ).…”

“…Some other nectar-feeding insects, i.e., nemestrinid or tabanid flies, display similar morphological adaptations comprising a long, slender T A B L E 4 Biometry of the proboscis (% indicate species with a proboscis longer or shorter than body length), galea (volumes of lumen and intragaleal musculature), the stipes pump (volumes of esm and ism), food canal volume, and suction pump (volumes of lumen, dilator muscles, and compressor musculature) proboscis and a smooth apical region with remarkably few and short sensilla (Karolyi et al, 2012(Karolyi et al, , 2014Krenn et al, 2021).…”