Characterization of Male-Produced Aggregation Pheromone of the Bean Flower Thrips Megalurothrips sjostedti (Thysanoptera: Thripidae)

Abstract

Aggregation of the bean flower thrips, Megalurothrips sjostedti (Trybom) (Thysanoptera: Thripidae), has been observed on cowpea, Vigna unguiculata (L.) Walp. To understand the mechanism underpinning this behavior, we studied the responses of M. sjostedti to headspace volatiles from conspecifics in a four-arm olfactometer. Both male and female M. sjostedti were attracted to male, but not to female odor. Gas chromatography/mass spectrometry (GC/MS) analyses revealed the presence of two distinct compounds in male M. sjostedti headspace, namely (R)-lavandulyl 3-methylbutanoate (major compound) and (R)-lavandulol (minor compound); by contrast, both compounds were only present in trace amounts in female headspace collections. A behavioral assay using synthetic compounds showed that male M. sjostedti was attracted to both (R)-lavandulyl 3-methylbutanoate and (R)-lavandulol, while females responded only to (R)-lavandulyl 3-methylbutanoate. This is the first report of a male-produced aggregation pheromone in the genus Megalurothrips. The bean flower thrips is the primary pest of cowpea, which is widely grown in sub-Saharan Africa. The attraction of male and female M. sjostedti to these compounds offers an opportunity to develop ecologically sustainable management methods for M. sjostedti in Africa.

Keywords: Grain legumes; Headspace analysis; Megalurothrips sjostedti; Olfactometer bioassay; Thrips pheromone.

Fig. 1

Behavioral responses of male Megalurothrips sjostedti to headspace volatiles collected from male or female conspecifics in a four-arm olfactometer. Each male thrips was observed for 12 min. Time spent (min; mean ± SE) by male M. sjostedti in the treatment and control regions of the olfactometer is shown. P indicates the level of significance for the difference between treatment and control

Fig. 2

Behavioral responses of female Megalurothrips sjostedti to headspace volatiles from male or female conspecifics in a four-arm olfactometer. Each female thrips was observed for 12 min. Time spent (min; mean ± SE) by female M. sjostedti in the treatment and control regions of the olfactometer is shown. P indicates the level of significance for the difference between treatment and control

Fig. 3

Mass chromatograms of the headspace volatiles from adult males (upper trace) and females (lower trace) of Megalurothrips sjostedti on a DB-5MS column. The two labeled compounds are (R)-lavandulol (A) and (R)-lavandulyl 3-methylbutanoate (B). TIC = total ion current

Fig. 4

Structures of major and minor compounds of male Megalurothrips sjostedti aggregation pheromone

Fig. 5

Behavioral responses of male Megalurothrips sjostedti to synthetic male-produced compounds in a four-arm olfactometer. Time spent (min; mean ± SE) by male M. sjostedti in the treatment and control regions of the olfactometer is shown. P indicates the level of significance for the difference between treatment and control

Fig. 6

Behavioral responses of female Megalurothrips sjostedti to synthetic male-produced compounds in a four-arm olfactometer. Time spent (min; mean ± SE) by female M. sjostedti in the treatment and control regions of the olfactometer is shown. P indicates the level of significance for the difference between treatment and control