A South African Scenario: Structure and Function of Peptides of the Adipokinetic Hormone Family of the Brown Locust, Locustana pardalina, and the Putative Role of These Peptides in Plague Management

The brown locust, Locustana pardalina, is a major agricultural pest in southern Africa during swarm formation. Like other locust species, L. pardalina has much higher carbohydrate concentrations in circulation than lipid; carbohydrates are predominantly used in the first minutes of flight and with sustained flight, the metabolic fuel switches to lipids mobilised from fat body stores. We isolated three peptides from the corpora cardiaca of the brown locust; through sequence elucidation by Edman degradation, mass spectrometry and chromatographic confirmation, we show that the brown locust has the same compliment of chemically isolated adipokinetic hormones (AKHs) as in Locusta migratoria: a decapeptide and two octapeptides; all increase the circulating lipid levels in locusts but not the carbohydrate concentration. During a rest period following flight, the carbohydrate levels in the haemolymph remained lower than before flight, whereas the lipid levels remained elevated. We show that the glycogen concentration in the fat body is significantly lowered after 1 h rest postflight and it is significantly increased in the flight muscles in this time. Thus, glycogen is mobilised from the fat body during the rest phase and transported as trehalose to the flight muscles and there, converted to glycogen, presumably to supply energy for a subsequent flight action. Finally, we discuss the molecular evolution of AKHs in Orthoptera and how two of the brown locust AKHs could serve as leads for developing peptidomimetics for combatting swarm outbreaks and reducing the need for harmful, indiscriminate chemical pesticides.