Defensive spiroketals from Asceles glaber (Phasmatodea): absolute configuration and effects on ants and mosquitoes

Insects are the largest and most diverse group of organisms on earth, with over 1,000,000 species identified to date. Stick insects ("walkingsticks" or "phasmids", Order Phasmatodea) are known for and name-derived from their camouflage that acts as a primary line of defense from predation. However, many species also possess a potent chemical defense spray. Recently we discovered that the spray of Asceles glaber contains spiroketals [a confirmed major component: (2S,6R)-(-)(E)-2-methyl-1,7-dioxaspiro[5.5]undecane, and a tentatively identified minor component: 2-ethyl-1,6-dioxaspiro[4.5]decane] and glucose. In this paper, we: 1) illustrate the identification of spiroketals and glucose in the defense spray of A. glaber by using Nuclear Magnetic Resonance (NMR), Gas Chromatography/Mass Spectrometry (GC/MS), and comparison with a synthetic reference sample; 2) provide the elucidation of the absolute configuration of the major spiroketal in that defense spray; and 3) demonstrate the effect of this compound and its enantiomer on both fire ants (Solenopsis invicta) and mosquitoes (Aedes aegypti).