Evidence for Aggregation Control by Cuticular Hydrocarbons in the European Earwig, Forficula auricularia

The European earwig, Forficula auricularia is a pestiferous insect, which has been introduced to most temperate regions of the world. Despite several attempts, the aggregation pheromone components used by F. auricularia remain unresolved. Furthermore, earwig population studies have shown that earwig aggregation sizes (trap catches) begin to decline soon after the imaginal moult. We attempt to isolate the aggregation pheromone used by F. auricularia and develop a synthetic pheromone blend for use in agricultural and urban pest management. Laboratory and field-based bioassays showed that earwig-exposed substrates are attractive to conspecifics. Solvent washes of earwig cuticles yield a total of 51 saturated, unsaturated and methyl-branched hydrocarbons (HC). Analysis of earwig-exposed substrates in both laboratory and field scenarios using GC-MS yielded numerous HCs. Field-based bioassays assessing a blend of four unsaturated HCs elicited significant behavioural responses on several occasions. However, these responses were not consistently observed. Sequential sampling of cuticular HCs from earwigs while simultaneously monitoring field populations over a five month field season demonstrated the production of the cuticular HCs fluctuates over time in adults. Moreover, the unsaturated HCs that elicited behavioural responses were shown to decline over time with this decline significantly correlating with the decline in earwig trap catches. We provide first evidence that F. auricularia utilise a suite of unsaturated cuticular HCs to mediate earwig aggregations and that these HCs decline after the imaginal moult, which initiates dispersal in earwig field populations prior to over-wintering.