Extremely long mouthparts in flower-visiting insects:
form, function and evolution

Extremely long mouthparts that serve for the uptake of nectar in flower visiting insects provide ample opportunity to examine constraints on organ evolution. The majority of the flower visiting insects are regarded as short-tongued since their mouthparts are shorter than the head, while extremely long proboscides, i.e., exceeding body length, are rare. Advantages of long proboscides have been previously formulated and tested in nectar feeding from long spurred flowers. The project represents the first attempt to evaluate the costs of long mouthparts. The research will compare flower-visiting insects which have an average-sized tubular proboscis with related species having extremely long mouthparts.

The estimation of anatomical and functional costs of extremely long proboscid mouthparts should contribute significantly to our understanding of the evolution of form and function in context with insect feeding behaviour on flowers.

Hypotheses

(1) Anatomical costs are optimized in those regions of the proboscis which are disproportionately elongated to the extent that they contain fewer muscles and sensillae compared to corresponding regions in average-sized proboscides of closely related species.

(2) Anatomical costs of variously long proboscides within a single species will provide an estimate of the extra expenses which accompany advances of proboscis elongation.

(3) Biometry and biomechanics of the suction pumps correlate with the proboscis length.

(4) Flower handling time should greatly increase in butterflies and nemstrinid flies with extremely long proboscides.

The study deals with hawk moths, neotropical butterfly of the families Riodinidae and Hesperiidae, neotropical bees (Euglossini) and South Africa tangle-veined fly (Nemestrinidae).

The microanatomical studies use electronmicroscopy and micro-CT as well as biometric analyses of body size and proboscis length. Field studies take place in the Tropical Biological Station La Gamba (Costa Rica) and in South Africa.

Fotos

Eurybia lycisca on an inflorescence of Calathea crotalifera		Euglossa sp. on an inflorescence of Calathea crotalifera		Proseoca sp. on Babiana praemorsa

Research team

Harald W. Krenn
Julia Bauder, PhD student
Florian Karolyi, PhD student
Maria Gruber, master student

Cooperation partners

Jonathan Colville
µCT and Morphometry Department of Theoretical Biology
Electronmicroscop Department of Cell Imaging and Ultrastructural Research

Congress activities

6th Conference on the Biology of Butterflies, Edmonton, Canada

Publications

Bauder JAS, Lieskonig N, Krenn HW (2011) The extremely long tongued Neotropical butterfly Eurybia lycisca (Riodinidae): Proboscis morphology and flower handling. Arthropod Structure & Development, in press