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

Abstract

Males of many tephritid fruit fly species of the genus Bactrocera show a very strong affinity to methyl eugenol (ME). An attracted male compulsively ingests ME, which is then biotransformed before its metabolites are accumulated into the rectal gland. The glandular organ is known to serve as a reservoir for sex pheromone in some species. Upon ME-feeding, males of the oriental fruit fly, Bactrocera dorsalis, selectively accumulated two metabolites, 2-allyl-4,5-dimethoxyphenol (DMP) and (E)-coniferyl alcohol (E-CF), in the rectal pheromone gland. We compared the profiles of phenylpropanoid metabolites accumulated by three other species of very high economic and quarantine importance-Bactrocera invadens, Bactrocera zonata and Bactrocera correcta, with that of B. dorsalis. Males of each species were fed artificially on ME and the metabolites stored in the rectal glands were examined by means of chromatography and spectroscopy. Similar to B. dorsalis, males of laboratory-raised B. invadens accumulated DMP and E-CF, in almost equal quantities, in the rectal sac. The sum of DMP and E-CF increased gradually with time after ME consumption and reached as high as 150 lg/male 2 days post ME-feeding. Wild males of B. invadens captured in Kenya also possessed both the compounds in varying quantities. In contrast, males of B. zonata accumulated DMP and (Z)-coniferyl alcohol (Z-CF) in an approximate ratio of 1:1; whereas B. correcta is known to convert ME to (Z)-3,4-dimethoxycinnamyl alcohol (Z-DMC) and Z-CF also in an approximately 1:1 ratio. Thus, there are three types of binary combinations of rectal phenylpropanoid volatiles (i.e. DMP ? E-CF; DMP ? Z-CF; Z-CF ? Z-DMC) utilized among the four Bactrocera species. Such differences in phenylpropanoid ingredients may play a critical role in differentiating these species if encountered in the natural habitat. In this context, the two putative sibling species-B. invadens and B. dorsalis, possess the identical subset of rectal volatiles (DMP and E-CF) in a similar proportion. Furthermore, the phylogenetic analyses of the four Bactrocera species by comparing nucleotide sequences in the mitochondrial genes showed that B. invadens clearly belonged to the same clade as B. dorsalis species. Therefore, we consider the two as the same biological species, and certainly not distinct.

Molecular clock analysis on fiveBactroceraspecies flies (Diptera: Tephritidae) based on combination ofCOIandNADHsequences

“…For this reason, several studies have been conducted to clarify the taxonomic puzzles, for example on taxonomy, molecular genetics, behaviour, chemical and cytogenetic reactions (Tan et al 2011;Khamis et al 2012;Schutze, Jessup, et al 2012Boykin et al 2013;Krosch et al 2013;Schutze et al 2013;Tan et al 2013). Despite the difficulties, several discoveries have been made at a basic level on its taxonomic situation via the implementation of the tools that have been discussed above.…”

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

“…Males of several other closely related Bactrocera species (B. carambolae, B. zonata, and B. correcta) fed on ME, selectively converted it into other unique subsets of ME-metabolites, including (Z)-coniferyl alcohol and (Z)-3,4-dimethoxycinnamyl alcohol, and stored these in the rectal gland. 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.…”

Mating Compatibility Among Four Pest Members of the <I>Bactrocera dorsalis</I> Fruit Fly Species Complex (Diptera: Tephritidae)

“…These taxonomic revisions were based predominantly on morphological characters; however, the characterization and analysis of allozyme data (Yong 1995), DNA information (Muraji and Nakahara 2002, Naeole and Haymer 2003, Armstrong and Ball 2005, Yu et al 2005, morphometric characters (Iwaizumi et al 1997;Adsavakulchai et al 1998;Iwahashi 1999a,b,;Mahmood 1999;Iwahashi 2001;Drew et al 2008), pheromone composition (Fletcher and Kitching 1995, Wee and Tan 2005, Tan et al 2011), and behavior (McInnis et al 1999Wee and Tan 2000a,b;Tan 2003), have since been applied to either support or challenge the existing classiÞcation, particularly of B. dorsalis, B. papayae, B. philippinensis, B. invadens, and B. carambolae.…”