Camphor and Borneol as the Male-Produced Sex Pheromone of the Shield Bug, Orsilochides leucoptera (Hemiptera: Scutelleridae)

The ability of stink bugs to release high amounts of strong-smelling and irritating defensive compounds is related to their metathoracic gland (MTG), which is an exocrine gland with defensive, sexual, alarm and aggregation signal functions. Orsilochides leucoptera (Scutelleridae) is a widespread species in the Neotropical region that feeds on plants of the families Malvaceae, Poaceae and Euphorbiaceae. A series of compounds (ketones, alcohols and esters) have been identified in the MTGs among the three species of Scutelleridae whose MTG secretions have been investigated thus far; however, no sex pheromone compounds have been described for any scutellerid species. The aim of this work was to study sex pheromone communication within this family of stink bugs, and identify the compounds present in the MTG of O. leucoptera. Analysis by gas chromatography/mass spectrometry (GC/MS) revealed two male specific compounds identified as (R)-camphor (1) and (R)-borneol (2), which were attractive to females in Y-tube olfactometer bioassays. Also, GC/MS analysis of secretions from MTG of males and females of O. leucoptera, identified eight additional compounds: 2-(E)-hexenal (3), (E)-4-oxo-2-hexenal (4), (E)-hex-2-enyl acetate (5), (R)-linalool (6), (R)-alpha-terpineol (7), dodecane (8), 1-tridecene (9) and n-tridecane (10). From these, (R)-alpha-terpineol was detected only in the gland of males, and is probably a biosynthetic intermediate of the pheromone components. Most of the MTG compounds identified in O. leucoptera have been identified in other heteropteran species. Camphor is often a toxic and repellent compound for insects. However, we report it, for the first time, as a sex pheromone component of an insect.