Metabolic aspects of flight in the dung beetle Pachylomerus femoralis (Kirby) (Coleoptera : Scarabaeidae)

Concentrations of potential energy substrates were measured in the haemolym ph and flight muscles of: the dung beetle Pachylomerus femoralis (Kirby). S amples were taken from beetles at rest, captured during flight of unknown l ength, collected immediately after voluntary termination of flight (without any traces of dung in the vicinity) and collected immediately upon arrival at pars of fresh cattle dung in the Sandveld Nature Reserve, Free State Pr ovince, South Africa. Resting beetles had high concentrations of proline in the haemolymph (approximately 145 mu mol/ml) and flight muscles (approxima tely 70 mu mol/g) but negligible concentrations of carbohydrates in the hae molymph (lower than 2 mg/ml) and glycogen in the flight muscles (approximat ely 0.1 mu mol glucose equivalents/g). The beetles that were captured durin g flight, collected after they had terminated flight voluntarily or were tr apped with fresh dung, had substantially lower proline levels in the haemol ymph and flight muscles than resting beetles, while alanine levels in both compartments were significantly higher than in resting beetles. There were no differences in carbohydrate levels (in haemolymph and flight muscles) an d lipid levels (haemolymph) between resting beetles and those that were act ive. From these results it was concluded that proline is the only energy su bstrate for flight in P. femoralis. Sufficient proline was available in the beetles each time it was measured. A lack of fuel is consequently not the reason for beetles to terminate flight.