Identification of a Sex Pheromone Produced by Sternal Glands in Females of the Caddisfly Molanna angustata Curtis

Abstract

In the caddisfly Molanna angustata, females produce a sex pheromone in glands with openings on the fifth sternite. Gas chromatographic analyses of pheromone gland extracts with electroantennographic detection revealed four major compounds that stimulated male antennae. These compounds were identified by means of gas chromatography-mass spectrometry and enantioselective gas chromatography as heptan-2-one, (S)-heptan-2-ol, nonan-2-one, and (S)-nonan-2-ol in the approximate ratio of 1:1:4:10, respectively. Field tests showed that the mixture of the two alcohols was attractive to males whereas addition of the corresponding ketones reduced trap catches. The sex pheromone of M. angustata, a species in the family Molannidae within the suborder Integripalpia, is similar to the pheromones or pheromone-like compounds previously reported from six other trichopteran families, including members of the basal suborder Annulipalpia. This suggests that minimal evolutionary change of the pheromone chemistry has taken place within the leptoceroid branch of integripalpian Trichoptera compared to the ancestral character state.

Exploring a key synapomorphy: correlations between structure and function in the sternum V glands of Trichoptera and Lepidoptera (Insecta)

“…1; ). These compounds are known attractants or at least elicit a response in male antennae (Löfstedt et al ., 1994, 2008; Zhu et al ., 1995; Kozlov et al ., 1996; Bergmann et al ., 2002). Thus, pheromone production is probably an ancestral function of the sternum V glands.…”

“…1), suggesting that the methylated 3‐ketones/ols have taken on the function of heptan‐2‐one/ol and nonan‐2‐one/ol. This is supported by male antennae reacting to, and males being attracted to, the methylated 3‐ketone/ols produced by conspecific females in Apataniidae + Limnephilidae (Trichoptera), and to heptan‐2‐one/ol and nonan‐2‐one/ol produced by conspecific females in other Amphiesmenoptera (Löfstedt et al ., 1994, 2008; Zhu et al ., 1995; Bjostad et al ., 1996; Jewett, Brigham & Bjostad, 1996; Kozlov et al ., 1996; Bergmann et al ., 2001, 2002; Bergmann, 2002).…”

“…A number of gland compounds were significantly correlated with one another (Table 1). A significant co‐occurrence of two gland compounds might be explained by shared biosynthetic pathways, as is the case for ketones and their corresponding alcohols (Löfstedt et al ., 2008). This explains the co‐occurrence of heptan‐2‐one and heptan‐2‐ol, nonan‐2‐one and nonan‐2‐ol, Z 6‐nonen‐2‐one and Z 6‐nonen‐2‐ol, 3‐hydroxy‐2‐butanon and 2,3‐butanediol.…”

“…The female gland products function as sex pheromones in a number of trichopterans in the suborders ‘Spicipalpia’ (‘Spicipalpia’, comprising four families, is most probably not monophyletic; although the spicipalpian families are consistently placed close to the base of Trichoptera, no consensus has emerged with regard to placing the families in either Annulipalpia or Integripalpia) (Löfstedt et al ., 1994) and Integripalpia (Resh & Wood, 1985; Bjostad, Jewett & Brigham, 1996; Bergmann, 2002; Löfstedt et al ., 2008), as well as in the lepidopteran family Eriocraniidae (Zhu et al ., 1995; Kozlov et al ., 1996). Female gland products are known to elicit electroantennogram (EAG) responses in male antennae in additional species (Bergmann et al ., 2001, 2002), and compounds similar to those that attract males are found in yet more species (Löfstedt et al ., 1994; Bergmann, 2002).…”

Environmental cues or conspecific attraction as causes for egg mass aggregation in hydrobiosid caddisflies

“…While the importance of oviposition pheromones in Trichoptera is unknown, sex pheromones are common in at least some caddisfly families (e.g. Resh & Wood, 1985;Löfstedt et al, 1994;Bjostad et al, 1996;Löfstedt et al, 2008), so it is plausible that ovipositon pheromones may also occur in this species.…”