Accumulation of Phenylpropanoid and Sesquiterpenoid Volatiles in Male Rectal Pheromonal Glands of the Guava Fruit Fly, Bactrocera correcta

Abstract

The guava fruit fly, Bactrocera correcta, is widely distributed in Thailand and other surrounding Southeast Asian countries, and, like the closely related sympatric species, the oriental fruit fly, B. dorsalis, infests various fruits, including guava, peach, and mango. Males of both B. correcta and B. dorsalis are strongly attracted to, and compulsively feed on, methyl eugenol (ME). Bactrocera dorsalis males fed on ME sequester its metabolite phenylpropanoids, (E)-coniferyl alcohol and 2-allyl-4,5-dimethoxyphenol, in the rectal pheromone gland. In contrast, B. correcta males fed on ME sequester two different metabolites, (Z)-coniferyl alcohol (ZCF) and (Z)-3,4-dimethoxycinnamyl alcohol (DMC), in the rectal gland. Examination of the temporal changes of ME metabolites in B. correcta male rectal glands revealed that the total of ZCF and DMC was as high as 100 μg/male at 24 hr after ME feeding. ZCF and DMC were detected in a large proportion of wild B. correcta males captured at various sites in Thailand. Since B. correcta and B. dorsalis are sympatric species in Thailand, these two different subsets of rectal phenylpropanoids could play a role to avoid interbreeding between the species. Further survey of wild flies in Thailand revealed that a large proportion of males of B. correcta store large quantities (over 250 μg/gland) of sesquiterpene hydrocarbons, including β-caryophyllene, α-humulene, and alloaromadendrene in the rectal gland in addition to, or instead of, ZCF and DMC. Laboratory-reared males also sequestered β-caryophyllene and α-humulene, along with ZCF and DMC, when the sesquiterpenes were artificially supplied together with ME. A field test demonstrated that a mixture (1:1) of β-caryophyllene and α-humulene attracted male B. correcta, albeit in smaller numbers than in traps baited with ME. The sequestration of sesquiterpenes, in addition to the different ME metabolites in the pheromone gland in B. correcta males, contrasts with the situation in B. dorsalis males, suggesting a potential role in intra and/or inter-specific interactions between these sympatric species.

Comparison of phenylpropanoid volatiles in male rectal pheromone gland after methyl eugenol consumption, and molecular phylogenetic relationship of four global pest fruit fly species: Bactrocera invadens, B. dorsalis, B. correcta and B. zonata

“…Interestingly, Z-DMC found in B. correcta was also detected occasionally as a trace component in the rectal gland of B. dorsalis males fed on ME; but only in very few individuals (Nishida et al 1988b). These studies should, however, consider that males of B. correcta have relatively more complicated sex pheromonal components than B. zonata in that, besides the two ME metabolites, it also accumulates large quantities of sesquiterpene hydrocarbons possibly incorporated pharmacophagously from various plant sources during its adult stage (Tokushima et al 2010). Differentiating the three species, B. correcta, B. dorsalis and B. zonata, chemotaxonomically by checking the composition of phenylpropanoid volatiles accumulated in their rectal glands after exposure to ME is a very sensitive and precise method compared with methods based on indistinct morphological characters.…”

“…An authentic sample of (Z)-coniferyl alcohol was obtained by stereo-selective synthesis (Tokushima et al 2010). Samples of synthetic 2-allyl-4,5-dimethoxyphenol and (E)-coniferyl alcohol were prepared previously (Nishida et al 1988a, b).…”

Chemical ecology of insect–plant interactions: ecological significance of plant secondary metabolites

“…71,72) A series of sesquiterpene hydrocarbons such as β-caryophyllene (47) was identified from the rectal gland of wild B. correcta males. 73) These pharmacophagously acquired rectal sequestrates (both phenylpropanoids and sesquiterpenes) were suggested to function possibly as a unique sex pheromone to attract conspecific females of this highly diverged species radiating from central Southeast Asia. Compound 47 was found to be a more attractive male lure than 44 in B. correcta, and 47 thus serves as a highly selective monitoring agent not attractive to other sympatric pest species in Thailand (unpublished results).…”

Attraction and Electroantennogram Responses of Male Mediterranean Fruit Fly to Volatile Chemicals from Persea, Litchi and Ficus Wood

“…Methyl eugenol is also a parapheromone and feeding attractant for the guava fruit fly, Bactrocera correcta (Bezzi). Tokushima et al (2010) found that methyl eugenol metabolites, which were different from those sequestered by B. dorsalis, and also sesquiterpenes including α-humulene and β-caryophylene were sequestered in the male pheromonal rectal glands. In contrast, male C. capitata do not interact with essential oils that contain α-copaene, and unless the α-copaene is present in a low concentration, males tend to arrest near the essential oil but not contact it (e.g., Steiner et al, 1957).…”

“…It has been suggested that presence of α-copaene as a contaminant in their sample may explain the observed attraction (Cossé et al, 1995). Grové et al (1998) subsequently showed that Tokushima et al 2010;3 Ibrahim et al 2010 male C. capitata were not attracted by β-caryophyllene in field tests. In our results, the amount of β-caryophyllene was much higher in PAMEX and PAM 3 than in PAM 2, the latter of which was one of the most attractive trees in this experiment.…”