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.

Fig. 1

Gas chromatographic analysis of an extract of female M. angustata fourth and fifth abdominal sternites. Simultaneous FID and EAD using a male antenna as detector. EAD-active compounds 1–4 were identified as heptan-2-one (1), (S)-heptan-2-ol (2), nonan-2-one (3), and (S)-nonan-2-ol (4)

Fig. 2

Attraction of male M. angustata to female extracts, alcohols and alcohols, mixed with ketones (Experiment 1). Amounts of synthetic compounds in micrograms. FE Female equivalent. Statistical significance of treatment effects (least squares means) analyzed by generalized linear model assuming Poisson error: F_5,52 = 1.04, P = 0.403

Fig. 3

Field trapping of M. angustata, comparing attractiveness of alcohols, ketones, and alcohols mixed with ketones (Experiment 2). Statistical significance of treatment effects (least squares means) analyzed by generalized linear model assuming Poisson error: F_5,54 = 2.98, P = 0.019. Values followed by the same letter are not significantly different (P  > 0.05)

Fig. 4

Field trapping of M. angustata, comparing attractiveness of different alcohol baits and a mixture of ketones (Experiment 3). Statistical significance of treatment effects (least squares means) analyzed by generalized linear model assuming Poisson error: F_5,84 = 2.93, P = 0.017. Values followed by the same letter are not significantly different (P  > 0.05)

Fig. 5

Field trapping of M. angustata, comparing attractiveness of (S)-heptan-2-ol, (S)-nonan-2-ol, and their mixture (Experiment 4). Statistical significance of treatment effects (least squares means) analyzed by generalized linear model assuming Poisson error: F_3,54 = 10.06, P < 0.001. Values followed by the same letter are not significantly different (P  > 0.05)

Fig. 6

Field trapping of M. angustata, comparing different amounts of (S)-heptan-2-ol added to (S)-nonan-2-ol (Experiment 5). Statistical significance of treatment effects (least squares means) analyzed by generalized linear model assuming Poisson error: F_3,73 = 2.83, P = 0.044. Values followed by the same letter are not significantly different (P  > 0.05)