The insects with the longest proboscis in relation to body length are the nectar-feeding Nemestrinidae. These flies represent important pollinators of the South African flora and feature adaptations to particularly long-tubed flowers. The present study examined the morphology of the extremely long and slender mouthparts of Nemestrinidae for the first time. The heavily sclerotized tubular proboscis of flies from the genus is highly variable in length. It measures 20-47 mm in length and may exceed double the body length in some individuals. Proximally, the proboscis consists of the labrum-epipharynx unit, the laciniae, the hypopharynx, and the labium. The distal half is composed of the prementum of the labium, which solely forms the food tube. In adaptation to long-tubed and narrow flowers, the prementum is extremelyelongated, bearing the short apical labella that appear only to be able to spread apart slightly during nectar uptake. Moving the proboscis from resting position under the body to a vertical feeding position is accomplished in particular by the movements of the laciniae, which function as a lever arm. Comparisons with the mouthparts of other flower visiting flies provide insights into adaptations to nectar-feeding from long-tubed flowers.

A well-developed suction pump in the head represents an important adaptation for nectar-feeding insects, such as Hymenoptera, Lepidoptera and Diptera. This pumping organ creates a pressure gradient along the proboscis, which is responsible for nectar uptake. The extremely elongated proboscis of the genus Prosoeca (Nemestrinidae) evolved as an adaptation to feeding from long, tubular flowers. According to the functional constraint hypothesis, nectar uptake through a disproportionately elongated, straw-like proboscis increases flower handling time and consequently lowers the energy intake rate. Due to the conspicuous length variation of the proboscis of Prosoeca, individuals with longer proboscides are hypothesised to have longer handling times. To test this hypothesis, we used field video analyses of flower-visiting behaviour, detailed examinations of the suction pump morphology and correlations of proboscis length with body length and suction pump dimensions. Using a biomechanical framework described for nectar-feeding Lepidoptera in relation to proboscis length and suction pump musculature, we describe and contrast the system in long-proboscid flies. Flies with longer proboscides spent significantly more time drinking from flowers. In addition, proboscis length and body length showed a positive allometric relationship. Furthermore, adaptations of the suction pump included an allometric relationship between proboscis length and suction pump muscle volume and a combination of two pumping organs. Overall, the study gives detailed insight into the adaptations required for long-proboscid nectar feeding, and comparisons with other nectar-sucking insects allow further considerations of the evolution of the suction pump in insects with sucking mouthparts.Electronic supplementary materialThe online version of this article (doi:10.1007/s00114-013-1114-6) contains supplementary material, which is available to authorized users.

Female Pangoniinae in the tabanid fly genus Philoliche can display remarkably elongated proboscis lengths, which are adapted for both blood- and nectar-feeding. Apart from their role as blood-sucking pests, they represent important pollinators of the South African flora. This study examines the morphology of the feeding apparatus of two species of long-proboscid Tabanidae: Philoliche rostrata and Philoliche gulosa – both species display adaptations for feeding from a diverse guild of long-tubed flowers, and on vertebrate blood. The heavily sclerotised proboscis can be divided into two functional units. The short, proximal piercing part is composed of the labrum-epipharynx unit, the hypopharynx and paired mandible and maxilla. The foldable distal part is composed of the prementum of the labium which solely forms the food canal and is responsible for nectar uptake via the apical labella. The proboscis works as a drinking straw, relying on a pressure gradient provided by a two-part suction pump in the head. Both proboscis and body lengths and suction pump dimensions show a significantly correlated allometric relationship with each other. This study provides detailed insights into the adaptations for a dual diet using an elongated sucking proboscis, and considers these adaptations in the context of the evolution of nectar feeding in Brachycera.

Flower visiting beetles possess numerous structural adaptations of their mouthparts to adhere and ingest pollen grains. Using a Cryo-SEM approach the examination of the mouthparts in rapidly frozen Cetonia aurata (Scarabaeidae) indicates a previously unknown technique of pollen uptake in Coleoptera. Cryo-SEM micrographs of the mouthparts reveal a fluid covering the bristles on the buccal surface. In this way the bristles of the galeae form a wet brush which represents the primary organ of pollen uptake. The fluid improves adhesion of pollen to bristles lacking any specialized adhering surface or highly sculptured cuticle as present in other pollen feeding Coleoptera. The well developed mola region of the otherwise non-biting mandibles of C. aurata indicates that these beetles open pollen grains mechanically before ingestion. Examination of gut content demonstrated that crushed and intact pollen occur in all regions. The Cryo-SEM method represents a new approach to study functional morphology including the interaction of microstructures and fluids on cuticular surfaces of insects.

Although anthophilous Coleoptera are regarded to be unspecialised flower-visiting insects, monkey beetles (Scarabaeidae: Hopliini) represent one of the most important groups of pollinating insects in South Africa’s floristic hotspot of the Greater Cape Region. South African monkey beetles are known to feed on floral tissue; however, some species seem to specialise on pollen and/or nectar. The present study examined the mouthpart morphology and gut content of various hopliine species to draw conclusions on their feeding preferences. According to the specialisations of their mouthparts, the investigated species were classified into different feeding groups. Adaptations to pollen-feeding included a well-developed, toothed molar and a lobe-like, setose lacinia mobilis on the mandible as well as curled hairs or sclerotized teeth on the galea of the maxillae. Furthermore, elongated mouthparts were interpreted as adaptations for nectar feeding. Floral- and folial-tissue feeding species showed sclerotized teeth on the maxilla, but the lacinia was mostly found to be reduced to a sclerotized ledge. While species could clearly be identified as floral or folial tissue feeding, several species showed intermediate traits suggesting both pollen and nectar feeding adaptations. Mismatches found between mouthpart morphology and previously reported flower visiting behaviours across different genera and species requires alternative explanations, not necessarily associated with feeding preferences. Although detailed examinations of the mouthparts allowed conclusions about the feeding preference and flower-visiting behaviour, additional morphological and behavioural investigations, combined with greater taxon sampling and phylogenetic data, are still necessary to fully understand hopliine host plant relationships, related to monkey beetle diversity.

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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.