Factors influencing the supercooling of tropical Arthropoda, especially locusts

Summary Mean supercooling points are given for a number of tropical arthropods (table 1). These are surprisingly low in view of the fact that, in many cases, the animals never experience frost in nature, and it is argued that the ability to supercool may be a taxonomic rather than an adaptive feature. Beetles (Ocnera hispida) and desert locusts (Schistocerca gregaria) that had been supercooled once, showed a significant reduction in their supercooling points. Migratory locusts (Locusta migratoria) did not do so (table 2). Hydration caused a significant reduction in the supercooling point of S. gregaria but not of L. migratoria (table 3). Starvation lowered, but not significantly, the supercooling point of S. gregaria, and significantly that of Rhodnius prolixus (table 4). Pre-conditioning (‘Mellanby effect’) has been shown to result in a lowering of the supercooling point, significant in S. gregaria but not in L. migratoria (table 5). This is not achieved by dehydration, the elimination of faeces, an increase in osmolarity or by the secretion of glycerol. It could, however, result from a change in the nature or location of food already in the alimentary canal.