The oriental fruit fly, Bactrocera dorsalis (Handel) is one of the most destructive pests of fruits. The discovery of methyl eugenol (ME) as a potent male attractant for this species has led to its successful use in area-wide fruit fly control programs such as male annihilation. While the antenna is recognized as primarily responsible for male flies' detection of attractants such as ME, little is known of the involvement of the maxillary palp. Using behavioral assays involving males with intact and ablated antennae and maxillary palp structures, we seek to ascertain the relative involvement of the maxillary palp in the ability of the male fly to detect ME. In cage bioassays (distance of ≤40 cm from the source), >97% of unmodified males will normally show a response to ME. Here, we showed that 17.6% of males with their antennae ablated were still attracted to ME versus 75.0% of males with their palps ablated. However, none of the antennae-ablated males were able to detect ME over a distance of >100 cm. Furthermore, wind tunnel bioassays showed that maxillary palp-ablated males took a significantly longer time compared to unablated males to successfully detect and eventually feed on ME. These results suggest that although the antennae are necessary for detection of ME over longer distances, at shorter distances, both antennae and maxillary palps are also involved in detecting ME. Hence, those palps may play a larger role than previously recognized in maneuvering males toward lure sources over shorter ranges.
Males of Bactrocera dorsalis (Diptera: Tephritidae) are attracted strongly to and feed compulsively on methyl eugenol (1,2-dimethoxy- 4 -(2-propenyl)benzene), a highly potent male attractant. Pharmacophagy of methyl eugenol results in the production of phenylpropanoids 2-allyl-4,5-dimethoxyphenol and (E)-coniferyl alcohol that are sequestered and stored in the rectal gland prior to release as sex pheromonal components during mating at dusk. While these pheromonal components have also been detected in the hemolymph and crop of methyl eugenol-fed males, there is currently little information on the transport of these compounds from the crop to rectal gland in male B. dorsalis. Therefore, using physiological techniques such as parabiosis, rectal gland transplantation and hemolymph transfusion coupled with gas chromatography-mass spectrometry (GC-MS) analyses, we were able to ascertain and confirm the role of the hemolymph in the transport of these sex pheromonal components from the crop to the rectal gland. Further, the temporal profile of these methyl eugenol-derived bioactive compounds in the hemolymph also shows an increase with time post-methyl eugenol-feeding, i.e., 2-allyl-4,5-dimethoxyphenol attaining maximum amounts 15 min after ME consumption and decreasing thereafter, while for (E)-coniferyl alcohol-the increase and decrease are more gradual. These results further demonstrate the ability of insect hemolymph to transport many diverse forms of bioactive molecules including attractant-derived sex pheromonal components.
After pharmacophagy of methyl eugenol (ME), males of Bactrocera carambolae (Diptera: Tephritidae) produced (E)-coniferyl alcohol (CF) along with its endogenously synthesized pheromonal compounds. CF was shown to be released into the air by the ME-fed males only during the courtship period at dusk and attracted significantly more males and females than the ME-deprived males in wind tunnel assays. However, earlier onset of sexual attraction and a higher mating success were observed only in the wind tunnel and field cage assays on the third day posttreatment of ME. Field cage observations on the male-to-male interaction indicated that the ME-deprived males did not exhibit aggregation behavior, but that ME feeding promoted aggregation behavior in B. carambolae. Field cage observations revealed that the ME-deprived males were not only attracted to the ME-fed males, but also appeared to feed on their anal secretions. The secretions were subsequently confirmed to contain CF along with endogenously produced pheromonal compounds. Results obtained for B. carambolae were compared to those previously obtained from its sibling species, Bactrocera dorsalis, and are discussed in light of species advancement in fruit fly-plant relationships.
It is widely believed that most orchid flowers attract insects by using deception or chemical rewards in the form of nectar. Flowers of Bulbophyllum vinaceum produce a large array of phenylpropanoids that lure tephritid fruit fly males and also act as floral reward, which the flies subsequently convert to pheromone components. The major floral volatile components identified are methyl eugenol (ME), trans-coniferyl alcohol (CF), 2-allyl-4,5-dimethoxphenol (DMP), and trans-3,4-dimethoxycinnamyl acetate, whereas the minor components are eugenol, euasarone, trans-3,4-dimethoxy cinnamyl alcohol, and cis-coniferyl alcohol. Among the various floral parts, the lip (which is held in a closed position up against the sexual organs) has the highest concentration of the major compounds. An attracted male fly normally lands on one of the petals before climbing up onto and forcing the "spring loaded" floral lip into the open position, hence exposing the floral sexual organs. The architecture and location of chemical attractants of the lip compel the fly to align itself along the lip's longitudinal axis in a precise manner. As the fly laps up the compounds and moves towards the base of the lip, it passes the point of imbalance causing the lip to spring back to its normal closed position. The fly is catapulted headfirst into the column cavity, and its dorsum strikes the protruding sticky base of the hamulus and adheres to it. The momentum of the fly and the structural morphology of the long stiff hamulus act to pry out the pollinia from its anther cover. Hence, the pollinarium (pollinia + hamulus) is detached from the flower and adhered to the fly's dorsum. In this unique mutualistic association, both species receive direct reproductive benefits--the flower's pollinarium is transported for cross pollination, and the fly is offered a bouquet of phenylpropanoids (synomone) that it consumes, converts, and/or sequesters as sex pheromonal components, thus enhancing sexual attraction and mating success.
Pieris rapae is a serious pest of brassicas worldwide. We performed de novo assembly of P. rapae transcriptome by next-generation sequencing and assembled approximately 65,727,422 clean paired-end reads into 32,118 unigenes, of which 13,585 were mapped to 255 pathways in the KEGG database. A total of 6173 novel transcripts were identified from reads directly mapped to P. rapae genome. Additionally, 1490 SSRs, 301,377 SNPs, and 29,284 InDels were identified as potential molecular markers to explore polymorphism within P. rapae populations. We screened and mapped 36 transcripts related to OBP, CSP, SNMP, PBAN, and OR. We analyzed the expression profiles of 7 selected genes involved in pheromone transport and degradation by quantitative real-time PCR; these genes are sex-specific and differentially expressed in the developmental stages. Overall, the comprehensive transcriptome resources described in this study could help understand and identify molecular targets particularly reproduction-related genes for developing effective P. rapae management tools.