The chemosensory basis for behavioral divergence involved in sympatric host shifts II: olfactory receptor neuron sensitivity and temporal firing pattern to individual key host volatiles

The Rhagoletis species complex has been a key player in the sympatric speciation debate for much of the last 50years. Studies indicate that differences in olfactory preference for host fruit volatiles could be important in reproductively isolating flies infesting each type of fruit via premating barriers to gene flow. Single sensillum electrophysiology was used to compare the response characteristics of olfactory receptor neurons from apple, hawthorn, and flowering dogwood-origin populations of R. pomonella, as well as from the blueberry maggot, R. mendax (an outgroup). Eleven volatiles were selected as stimuli from behavioral/electroantennographic studies of the three R. pomonella host populations. Previously, we reported that differences in preference for host fruit volatile blends are not a function of alterations in the general class of receptor neurons tuned to key host volatiles. In the present study, population comparisons involving dose-response trials with the key volatiles revealed significant variability in olfactory receptor neuron sensitivity and temporal firing pattern both within and among Rhagoletis populations. It is concluded that such variability in peripheral sensitivity and temporal firing pattern could influence host preference and contribute to host fidelity and sympatric host shifts in the Rhagoletis comple

Silent genes and rare males: A fresh look at pheromone blend response specificity in the European corn borer moth, Ostrinia nubilalis

The response of male moths from two pheromone races of the European corn borer, Ostrinia nubilalis, was measured in a flight tunnel assay to different ratios of structurally different compounds that comprise the sex pheromone of the Asian corn borer, Ostrinia furnacalis. For both O. nubilalis races, between 1 and 5% of the males completed upwind flights to two different blends of the O. furnacalis pheromone components (the 2:1 Z/E12-14:OAc female-produced blend, and a 97:3 Z/E mix), confirming that rare males exist in the O. nubilalis populations that can detect and respond to mixtures of the O. furnacalis pheromone components. Rare males that responded to the O. furnacalis blends also responded to their own O. nubilalis blends (97:3 or 1:99 Z/E11-14:OAc), indicating that rare O. nubilalis males are not preferentially sensitive to mixtures of the O. furnacalis compounds, but rather that they have a broad range of response specificity, which includes recognition of a wide range of conspecific female-produced ratios, and also recognition of heterospecific mixtures. The results support the hypothesis that saltational shifts in pheromone blend composition (Roelofs et al., 2002) can lead to the evolution of a new species-specific communication system, in part because the broad response specificity of some males includes the ability to respond in an agonistic manner to novel mixtures of compounds. Abbreviation: / E race: using a 1:99 Z/E11-14:Oac blend Z race: using a 97:3 Z/E11-14:OAc blend Z/E-11: the European corn borer, O. nubilalis, blends (Z/E11-14:OAc). Z/E-12: the Asian corn borer, O. furnacalis, blend (Z/E12-14:OAc). bivoltine: one generation per year univoltine: two generations per yea

More Rare Males in Ostrinia: Response of Asian Corn Borer Moths to the Sex Pheromone of the European Corn Borer

A previous flight tunnel study showed that 3-5% of European corn borer (ECB) moths, Ostrinia nubilalis (Z/E11-14:OAc), could fly upwind and make contact with sources releasing the sex pheromone of the related Asian corn borer (ACB), Ostrinia furnacalis (2:1 Z/E12-14:OAc). In this study, we show that rare males (3-4%) are also present in South Korean ACB that respond to the sex pheromone blends of the ECB UZ (97:3 Z/E11-14:OAc) and BE (1:99 Z/E11-14:OAc) pheromone races. We also show that the upwind flight response of a significant proportion of male ACB was antagonized by the addition of 1% Z9-14:OAc to the ACB blend, a compound that also antagonizes the upwind flight of ECB males. Male ACB flight behavior was not, however, affected by adding either of the ECB blends to the ACB blend, or by the addition of 50% 14:OAc, a compound identified from female pheromone glands of ACB and a number of other Ostrinia species. Additional flight tunnel tests with ACB to study the comparative aspects of ECB and ACB pheromone response specificity showed that male ACB exhibited maximal levels of upwind flight and source contact with doses of pheromone (30 and 100μg on rubber septum sources) that also elicited maximal levels in the two ECB pheromone races. The maximal level of source contact for ACB (66%) was lower than observed with the UZ race of ECB to its pheromone blend (>95%), but comparable to those for the BE race of ECB (65-70%). Male ACB also flew upwind in high proportions to a broader range of ratios of Z/E12-14:OAc (80:20 to 20:80) than was previously observed for either of the ECB race

Identification of Host Fruit Volatiles from Flowering Dogwood ( Cornus florida ) Attractive to Dogwood-Origin Rhagoletis pomonella Flies

Solid-phase microextraction and gas chromatography coupled with electroantennographic detection were used to identify volatiles from fruit of flowering dogwood, Cornus florida, as key attractants for Rhagoletis pomonella flies originating from dogwood fruit. A six-component blend containing ethyl acetate (54.9%), 3-methylbutan-1-ol (27.5%), isoamyl acetate (0.9%), dimethyl trisulfide (1.9%), 1-octen-3-ol (9.1%), and β-caryophyllene (5.8%) was identified from flowering dogwood fruit that gave consistent EAD activity. In a flight tunnel assay there was no significant difference in the response of individual dogwood flies exhibiting upwind anemotactic flight to volatile extracts from dogwood fruit and the six-component synthetic mixture. Dogwood flies also displayed significantly greater levels of upwind flight to sources with the dogwood volatile blend than with previously identified volatile blends from domestic apple or hawthorn fruit. Selected subtraction assays showed that the three-component mixture of 3-methylbutan-1-ol, 1-octen-3-ol, and β-caryophyllene elicited levels of upwind flight to the source equivalent to the six-component mixture. Our study adds to previous ones showing that populations of Rhagoletis pomonella flies infesting apple, hawthorn, and flowering dogwood fruit are attracted to unique mixtures of fruit volatiles, supporting the hypothesis that host fruit odors could be key traits in sympatric host shifts and establishing host fidelity within members of the Rhagoletis pomonella species comple

The chemosensory basis for behavioral divergence involved in sympatric host shifts. I. Characterizing olfactory receptor neuron classes responding to key host volatiles

The recent shift of Rhagoletis pomonella from its native host hawthorn to introduced, domestic apple has been implicated as an example of sympatric speciation. Recent studies suggest that host volatile preference might play a fundamental role in host shifts and subsequent speciation in this group. Single sensillum electrophysiology was used to test a proposed hypothesis that differences in R. pomonella olfactory preference are due to changes in the number or odor specificity of olfactory receptor neurons. Individuals were analyzed from apple, hawthorn, and flowering dogwood-origin populations, as well as from the blueberry maggot, Rhagoletis mendax Curran (an outgroup). Eleven compounds were selected as biologically relevant stimuli from previous electroantennographic/behavioral studies of the three R. pomonella populations to host fruit volatiles. Cluster analysis of 99 neuron responses showed that cells from all tested populations could be grouped into the same five classes, ranging from those responding to one or two volatiles to those responding to several host volatiles. Topographical mapping also indicated that antennal neuron locations did not differ by class or fly taxa. Our results do not support the hypothesis that differences in host preference among Rhagoletis populations are a result of alterations in the number or class of receptor neurons responding to host volatile

Emergence, Mating, and Postmating Behaviors of the Oriental Beetle (Coleoptera: Scarabaeidae)

In a previous field-trapping study of the oriental beetle, Exomala orientalis (Waterhouse), by using synthetic sex pheromone on golf course fairways, numerous males were observed and trapped during the hours of peak mating activity. However, very few beetles were observed in the same areas when synthetic pheromone was absent. To investigate the hypothesis that mating in nature occurs cryptically within vegetation at the soil surface, laboratory studies on female emergence and pheromone release, male emergence and mate-locating, and female and male mating behaviors were conducted. Mate acquisition and copulation occurred on the soil surface near the female emergence site, with both sexes engaging in pheromone-mediated behaviors after having emerged from the soil. A highly stereotyped female pheromone release, or calling, behavior was observed, consisting of insertion of the female's head into the soil and elevation of the tip of her abdomen into the air. Bioassays conducted in a wind tunnel that simulated a turf fairway environment showed that walking and flying were both important in the upwind response of males to females. Mating and copulation occurred without an obvious complex courtship, but observations of postmating behaviors suggested that mate guarding occur

Experimental Evidence for Three Pheromone Races of the Scarab Beetle Phyllophaga anxia (LeConte)

This study offers experimental evidence for the existence of three pheromone races of the northern genitalic form of Phyllophaga anxia: one race in which females produce and males respond mainly to l-valine methyl ester, a second producing and responding to l-isoleucine methyl ester, and a third producing and responding to an intermediate range of blends of the two compounds. At Franklinville, NY, pheromone gland contents of females were analyzed using coupled gas chromatography-electroantennogram detection. Two types of females were found, one that produced greater than 99% l-valine methyl ester and another that produced greater than 99% l-isoleucine methyl ester. Capture-mark-release-recapture field tests with males at Franklinville established that most males were recaptured in traps baited with the same blends with which they were originally captured. The populations characterized at Franklinville, NY, have also been found at numerous locations from eastern Canada and the northeast and north central USA, sometimes in allopatry and sometimes in sympatry. At a site in Carver, MA, P. anxia males responded to blends of the methyl esters of l-valine and l-isoleucine, and Carver females produced blends similar to those to which the males responded. Populations responding to blends have been identified only from southeastern Massachusetts and Rhode Island. At a field site near Waterloo, NY, the addition of small proportions of l-isoleucine methyl ester to lures containing l-valine methyl ester did not affect trap captures, but higher proportions of l-isoleucine methyl ester were inhibitory, decreasing trap capture

Characterization of Z/E11- and Z9-desaturases from the obliquebanded leafroller moth, Choristoneura rosaceana

A ▵11-desaturase gene was cloned from the sex pheromone gland of the obliquebanded leafroller moth, Choristoneura rosaceana. The desaturase cDNA sequence spans 1300 nucleotides with an open reading frame encoding a 335 amino-acid protein, which has 81% identity to a Z/E11-desaturase of the redbanded leafroller moth, Argyrotaenia velutinana. A functional assay with a pYES2 yeast expression system demonstrated that the ▵11-desaturase exhibits unusual substrate and stereospecificities in producing a Z/E11 mixture (7:1) of only C14 acids. A metabolic Z9-desaturase also was cloned from fat body of this species, and proved to be in the class that produces more Z9-16:Acid than Z9-18:Acid

Support for ( Z )-11-Hexadecanal as a Pheromone Antagonist in Ostrinia nubilalis: Flight Tunnel and Single Sensillum Studies with a New York Population

The flight-tunnel response of male Z-strain European corn borer moths (ECB), Ostrinia nubilalis, from a population in New York State (USA), was significantly antagonized by addition of 1% (Z)-11-hexadecanal (Z11-16:Ald) to their sex pheromone (a 97:3 mix of (Z)- and (E)-11-tetradecenyl acetate [Z/E11-14:OAc]). The level of antagonism was equivalent to that observed for the previously identified ECB antagonist, (Z)-9-tetradecenyl acetate (Z9-14:OAc), and supports a recent report showing that Z11-16:Ald, a minor pheromone component of the Noctuid moth, Sesamia nonagrioides, caused antagonism of ECB pheromone communication in sympatric populations in the Iberian Peninsula. Single-sensillum recordings from ECB antennae, which included cross-adaptation experiments, showed that the same olfactory receptor neuron processing Z9-14:OAc inputs was responsible for detecting Z11-16:Ald, and that this neuron was not responsive to two other aldehydes, (Z)-9-tetradecanal (Z9-14:Ald) and (Z)-9-hexadecanal (Z9-16:Ald), found in other moth sex pheromones. Our results show that the antagonism is not confined to one geographic region, is specific for Z11-16:Ald, and that antagonist pathways might have the potential for processing a number of structurally similar compound