Suk Ling Wee

Chemical mimicry of insect oviposition sites: a global analysis of convergence in angiosperms

Floral mimicry of decaying plant or animal material has evolved in many plant lineages and exploits, for the purpose of pollination, insects seeking oviposition sites. Existing studies suggest that volatile signals play a particularly important role in these mimicry systems. Here, we present the first large-scale phylogenetically informed study of patterns of evolution in the volatile emissions of plants that mimic insect oviposition sites. Multivariate analyses showed strong convergent evolution, represented by distinct clusters in chemical phenotype space of plants that mimic animal carrion, decaying plant material, herbivore dung and omnivore/carnivore faeces respectively. These plants deploy universal infochemicals that serve as indicators for the main nutrients utilised by saprophagous, coprophagous and necrophagous insects. The emission of oligosulphide-dominated volatile blends very similar to those emitted by carrion has evolved independently in at least five plant families (Annonaceae, Apocynaceae, Araceae, Orchidaceae and Rafflesiaceae) and characterises plants associated mainly with pollination by necrophagous flies and beetles.

Comparative sensitivity to and consumption of methyl eugenol in three Bactrocera dorsalis (Diptera: Tephritidae) complex sibling species

Summary. Sensitivities to methyl eugenol of three sibling species in the Bactrocera dorsalis complex were compared. The degree of species sensitivity to methyl eugenol, i.e. B. dorsalis > B. papayae > B. carambolae (in decreasing order), was concomitant with the species age-related response to methyl eugenol as previously reported. The ability to consume methyl eugenol by the three sibling species showed similar trend - the average ME consumption per male was 0.70 ml for B. dorsalis, 0.58 ml B. papayae and 0.18 μl B. carambolae. Results obtained were discussed in relation to area-wide control of fruit fly.

Pharmacophagy of methyl eugenol by males enhances sexual selection of Bactrocera carambolae.

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.

Sexual maturity and intraspecific mating success of two sibling species of the Bactrocera dorsalis complex

Bactrocera carambolae Drew & Hancock and B. papayae Drew & Hancock (Diptera: Tephritidae), two closely related sibling species in the B. dorsalis (Hendel) complex were shown to have different rates of sexual maturity. The response of B. carambolae males to methyl eugenol was observed to begin 10 days after emergence and increased with age. The attractancy peaked at 28 days after emergence and above. The males were also found to require a higher dosage of methyl eugenol (1 mg) for optimal response. These results are in contrast with those of B. papayae reported previously. The response to methyl eugenol was also observed to correspond with the age when first mating was performed.

Phenylpropanoids in the fragrance of the fruit fly orchid, Bulbophyllum cheiri, and their relationship to the pollinator, Bactrocera papayae

Flowers of a southeast Asian orchid, Bulbophyllum cheiri, attract males of Bactrocera papayae and other fruit fly species sensitive to methyl eugenol for pollination. In addition to the major attractive component methyl eugenol, several other related phenylpropanoids were identified as minor components from the floral extracts. 2-Allyl-4,5-dimethoxyphenol, known as an element of sex and aggregation pheromone of B. papayae males was detected as a significant volatile ingredient together with its O-methyl ether (euasarone). The attractancy of each floral component and efficiency of incorporation of these phenylpropanoids into the rectal pheromone glands were examined in B. papayae males.

Evidence of Natural Hybridization Between Two Sympatric Sibling Species of Bactrocera dorsalis Complex Based on Pheromone Analysis

Bactrocera carambolae and B. papayae are major fruit fly pests and sympatric sibling species of the B. dorsalis complex. They possess distinct differences in male pheromonal components. In the 1990’s, wild Bactrocera fruit flies with morphological traits intermediate between those of B. carambolae and B. papayae were often captured in traps baited with methyl eugenol (ME). Chemical analyses of rectal glands of ME-fed males revealed that the laboratory F1, F2, and backcross hybrids possessed ME-derived sex pheromonal components ranging from that typical of B. papayae to that of B. carambolae without any specific trend, which included a combination of pheromonal components from both parental species within an individual hybrid. ME-fed hybrids without any ME-derived pheromonal components were also detected. Further chemical analysis of rectal glands from wild Bactrocera males, after ME feeding in the laboratory, showed a combination of pheromonal components similar to that found in the ME-fed, laboratory-bred hybrids. These findings present circumstantial evidence for the occurrence of a natural hybrid of the two Bactrocera species.

Re-examining the relationship between sexual maturation and age of response to methyl eugenol in males of the oriental fruit fly

Males of the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), are strongly attracted to, and feed voraciously on, methyl eugenol (ME) and use metabolites of this chemical to synthesize their sex pheromone. Previously, Wong et al. (1989 ) proposed that B. dorsalis males were attracted to ME even before attaining sexual maturity. However, their interpretation is possibly confounded by the fact that, in monitoring age‐related mating readiness, males were presented with equal‐aged females. As a result, if females mature more slowly than males, the age of male sexual maturation may have been overestimated, which may have accounted for the discrepancy observed between male age of ME responsiveness and mating activity. Here, we re‐examined the relationship between male age and mating readiness by comparing male mating activity when presented with same‐aged females vs. sexually mature females. In addition, we measured the age‐dependent response of B. dorsalis males to ME by recording (i) capture in ME‐baited traps, and (ii) feeding duration on ME‐containing paper discs. Our data support the conclusion of Wong et al. (1989 ) that B. dorsalis males show attraction to, and feed on, ME before attaining sexual maturity, but suggest that a marked difference in ME response and mating activity exists over a shorter age interval than indicated by Wong et al. (1989 ). Early attraction to, but not ingestion of, ME was related to accelerated sexual maturation. Unexpectedly, ingestion of ME by sexually immature males did not boost their mating success in trials conducted 10 days after feeding on the lure.

Effects of Substerilizing Doses of Gamma Radiation on Adult Longevity and Level of Inherited Sterility in Teia anartoides (Lepidoptera: Lymantriidae)

Abstract The effects of substerilizing doses of gamma radiation on the longevity and level of inherited sterility in the Australian moth Teia anartoides Walker were determined. Six day-old male pupae were treated with 0, 100, and 160 Gy of gamma radiation by using a 1.25 MeV Cobalt60 irradiation source. Laboratory studies of male longevity showed that radiation had little impact in adult moths of the P1, F1, and F2 generations. Inherited deleterious effects resulting from irradiation were observed in the progeny of F1 and F2 generations. Outcrosses between substerile parental males or their highly sterile male progeny to wild-type females did not affect female fecundity. However, adverse effects were observed for these crosses in the rates of successful egg hatch and postembryonic development. Fertility was always greater in out-crosses involving a P1 male than in any of the F1 out-crosses. F1 males were always more sterile than F1 females, and the level of sterility for the F1 and F2 generations was higher than that of the controls. The incidence of larval and pupal mortality was higher in the F2 than the F1 generation. A dose of 100 Gy had the highest success in inducing deleterious effects that were inherited through to the F2 generation. Our results indicated that the use of partially sterilizing doses of radiation has good potential as a selective strategy for management or eradication of T. anartoides.

Cytological Attributes of Sperm Bundles Unique to F1 Progeny of Irradiated Male Lepidoptera: Relevance to Sterile Insect Technique Programs

ABSTRACT The unique genetic phenomena responsible for inherited F1 sterility in Lepidoptera and some other arthropods provide advantages for the use of inherited sterility in a sterile insect technique (SIT) program. Lepidopteran females generally can be completely sterilized at a dose of radiation that only partially sterilizes males of the same species. When these partially sterile males mate with fertile females, many of the radiation-induced deleterious effects are inherited by the F1 generation. At the appropriate dose of radiation, egg hatch of females mated with irradiated males is reduced and the resulting (F1) offspring are both highly sterile and predominantly male. Lower doses of radiation used to induce F1 sterility increase the quality and competitiveness of the released insects. However, during a SIT program it is possible that traps used to monitor wild moth populations and over-flooding ratios (marked released males vs unmarked wild males) may capture unmarked F1 sterile males that cannot be distinguished from wild fertile males. In this study we developed a cytological technique with orcein and Giemsa stains to distinguish adult F1 progeny of irradiated males and fertile males. Our observations on 6 pest species in 5 families of Lepidoptera indicate that F1 males (sterile) from irradiated fathers can be distinguished from fertile males by the nuclei cluster in the eupyrene sperm bundles. The nuclei cluster in the fertile males exhibited a regular and organized arrangement of the sperm and was homogeneously stained, whereas in F1 males the nuclei cluster of sperm was disorganized, irregular and unevenly stained. Supplementary Material: color illustrations are available online at http://www.fcla.edu/FlaEnt/fe921.htm

Comparison of methyl eugenol metabolites, mitochondrial COI, and rDNA sequences of Bactrocera philippinensis (Diptera: Tephritidae) with those of three other major pest species within the dorsalis complex

Males of the oriental fruit fly, Bactrocera dorsalis (Hendel) and some of its sibling species have strong affinity for methyl eugenol (ME). Methyl eugenol ingested by male flies is biotransformed in the crop to two ME metabolites that eventually accumulate in the rectal gland, which is known to serve as a reservoir for B. dorsalis sex pheromones. When fed with ME, males of laboratory and wild B. philippinensis Drew and Hancock selectively accumulated two metabolites, 2-allyl-4,5-dimethoxyphenol and (E)-coniferyl alcohol, in the rectal gland, as was seen for B. dorsalis sensu stricto, B. invadens Drew, Tsuruta and White, and B. papayae Drew and Hancock. Phylogenetic analysis of COI and rDNA sequence data of these four taxa also revealed a close relationship among B. philippinensis, B. dorsalis s.s., B. invadens, and B. papayae (all four are members of the dorsalis species complex). This result corroborates pheromone analysis. The usefulness of pheromonal analysis as a chemotaxonomy tool to complement molecular and other analysis in differentiation of closely related sibling species within the Bactrocera dorsalis complex, for which use of morphological characters had been inadequate, is highlighted.