Diversity and sex differences in rectal gland volatiles of Queensland fruit fly, Bactrocera tryoni (Diptera: Tephritidae)

Abstract

Rectal gland volatiles are key mediators of sexual interactions in tephritid fruit flies. We used solid-phase microextraction (SPME) plus gas chromatography-mass spectrometry (GC-MS) and gas chromatography-flame ionization detection (GC-FID) to substantially expand rectal gland chemical characterisation of the Queensland fruit fly (Bactrocera tryoni (Diptera: Tephritidae); Qfly). The SPME GC-MS analysis identified 24 of the 30 compounds previously recorded from Qfly rectal glands, plus another 21 compounds that had not previously been reported. A few amides and fatty acid esters dominated the chromatograms of males and females respectively, but we also found other esters, alcohols and aldehydes and a ketone. The GC-FID analyses also revealed over 150 others, as yet unidentified, volatiles, generally in lesser amounts. The GC-FID analyses also showed 49 and 12 compounds were male- and female-specific, respectively, both in single sex (virgin) and mixed sex (mostly mated) groups. Another ten compounds were male-specific among virgins but undetected in mixed sex groups, and 29 were undetected in virgins but male-specific in mixed sex groups. The corresponding figures for females were four and zero, respectively. Most short retention time peaks (including a ketone and an ester) were male-specific, whereas most female-biased peaks (including five fatty acid esters) had long retention times. Our results indicate previously unsuspected diversity of rectal gland volatiles that might have pheromone functions in males, but far fewer in females.

Genetic variation for rectal gland volatiles among recently collected isofemale lines and a domesticated strain of Queensland fruit fly, Bactrocera tryoni (Diptera: Tephritidae)

“…(hereafter denoted mixed males and mixed females, respectively) were obtained from cages containing both sexes, 90-95% of females from which had been mated [47].…”

“…Qfly females also secrete diverse volatiles from their rectal glands, including lesser amounts of some of the amides found in males, with their profiles instead dominated by fatty acid esters [47,57,60,61]. Overall a majority of the volatiles secreted from Qfly rectal glands show at least quantitative and in many cases presence/absence differences between the sexes [47].…”

“…Male rectal glands have been shown to produce many of these compounds in various tephritids, including the Mexican fruit fly, Anastrepha ludens [35,36], Mediterranean fruit fly, Ceratitis capitata [37][38][39][40], Oriental fruit fly, Bactrocera dorsalis [41,42] and Queensland fruit fly (Qfly), Bactrocera tryoni [31,[43][44][45][46]. Comparative analyses have shown substantial qualitative and quantitative divergence in rectal gland volatiles among Bactrocera species [47,48].…”

“…Sexually mature Qfly males release a blend of volatiles from their rectal glands and disperse them via rapid wing vibrations ('calling') to attract females [31,[52][53][54][55][56]. Over 100 volatile compounds have been found in the rectal glands of Qfly males, and over 30 of these have been identified [47,57]. The most abundant compounds are aliphatic amides [43,58,59].…”

“…Qfly females also secrete diverse volatiles from their rectal glands, including lesser amounts of some of the amides found in males, with their profiles instead dominated by fatty acid esters [47,57,60,61]. Overall a majority of the volatiles secreted from Qfly rectal glands show at least quantitative and in many cases presence/absence differences between the sexes [47]. Less is known about the functions of the volatile compounds emitted by female Qflies [62,63], although work on other tephritids has implicated their female rectal gland volatiles in some mating and other reproductive behaviours [41, [64][65][66].…”