In contrast to other social insects, no volatile components have yet been identified from the common wasp P. uulgaris ['l. After the identification of 2-ethyl-l,6-dioxaspiro[4.5]nonane (chalcogran) ( 1 )[' I as the principal aggregation pheromone of Pityogenes chalcographus L., we have now studied the massspectrometric fragmentation of volatile spiroketal~[~] and found spiroketals to be present in the pentane extracts of the abdomina of P. uulgaris workers.
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The main component and a trace substance proved to be, respectively, (2)-and (E)-7-methyl-l,6-dioxaspiro[4.5]decane (2)r5I, while two minor components were identified as equal amounts of (Z)-and (E)-2-methyl-l,6-dioxaspiro[4.5]decane (3)c61, along with traces of 2-nonanone. The racemic compounds (2) and ( 3 ) were prepared from y-butyrolactone and 6-caprolactone, and y-valerolactone and &valerolactone, respectively, according to the procedure of Erdmann and Strom['I. The synthetic substances purified by preparative GLC showed the same mass spectra and had similar retention times on GLC as the natural products, the chirality of which have not yet been clarified. Remarkably, the new spiroketals (2) and (3) show an unbranched dihydroxynonanone skeleton, as do chalcogran ( I ) , 7-ethyl-5-methyl-6,8-dioxabicyclo[3.2.1]octane (brevicomin) (4)[81, and 1,3-dimethyl-2,9-dioxabicyclo[3.3.l]nonane (5)f91. ( 4) is an attractant, and ( 5 ) is a compound occurring specifically in attacked spruce. Genetic relations cannot be excluded.
Preliminary bioassays showed that the new compounds might serve as repellents or aggression inhibitors, which could protect the individuals from attack by its fellow wasps. Dead extracted wasps hanging 12cm in front of the entrance hole of an earth nest frequented by 40 individuals per minute were attacked within two minutes and then at intervals of 30-60 s. In contrast, extracted wasps previously treated with 0.1 mg of the spiroketals mixed in the naturally occurring proportions or freshly killed ones were only attacked after 8-10 min, the intervals between further attacks being much longer than before. Application of 0.1 mg of the spiroketal mixture to heavily frequented dummies inhibited any attack for 8-12min. Each series of assays was repeated twelve times.