RESUMEN

Aggregation of the German cockroach, Blattella germanica, is regulated by fecal aggregation agents (pheromones), including volatile carboxylic acids (VCAs). We demonstrate that the gut microbial community contributes to production of these semiochemicals. Chemical analysis of the fecal extract of B. germanica revealed 40 VCAs. Feces from axenic cockroaches (no microorganisms in the alimentary tract) lacked 12 major fecal VCAs, and 24 of the remaining compounds were represented at extremely low amounts. Olfactory and aggregation bioassays demonstrated that nymphs strongly preferred the extract of control feces over the fecal extract of axenic cockroaches. Additionally, nymphs preferred a synthetic blend of 6 fecal VCAs over a solvent control or a previously identified VCA blend. To test whether gut bacteria contribute to the production of fecal aggregation agents, fecal aerobic bacteria were cultured, isolated, and identified. Inoculation of axenic cockroaches with individual bacterial taxa significantly rescued the aggregation response to the fecal extract, and inoculation with a mix of six bacterial isolates was more effective than with single isolates. The results indicate that the commensal gut microbiota contributes to production of VCAs that act as fecal aggregation agents and that cockroaches discriminate among the complex odors that emanate from a diverse microbial community. Our results highlight the pivotal role of gut bacteria in mediating insect-insect communication. Moreover, because the gut microbial community reflects the local environment, local plasticity in fecal aggregation pheromones enables colony-specific odors and fidelity to persistent aggregation sites.

Asunto(s)

Asunto(s)

RESUMEN

Oil-coated clear panel traps baited with a host plant-based kairomone lure have successfully been used for monitoring female grape berry moth, Paralobesia viteana (Clemens) (Lepidoptera: Tortricidae), but low capture rates as well as difficulty in servicing these traps makes them unsuitable for commercial use. We compared the performance of different trap designs in a flight tunnel and in a vineyard by using a 7-component synthetic kairomone blend, with a focus on trap visual cues. In flight tunnel experiments, a clear delta trap performed better than other traps. When we tested clear delta, green delta, or clear wing traps baited with a cut grape shoot, >50% of female grape berry moths made complete upwind flights. However, the clear delta trap was the only design that resulted in female moths entering the trap. Similar results were observed when females were tested with different traps (clear delta, green delta, white delta, clear wing, or green wing traps) baited with the kairomone lure. Adding a visual pattern that mimicked grape shoots to the outside surface of the clear delta trap resulted in 66% of the females that made upwind flights entering the trap. However, the positive effect of adding a visual pattern to the trap was not observed in a vineyard setting, where clear delta traps with or without a visual pattern caught similar numbers of females. Still, the number of male and female grape berry moths captured in clear delta traps with or without a visual pattern was not significantly different from the number of male and female grape berry moths captured in panel traps, suggesting that the use of these delta traps could be a less cumbersome alternative to oil-coated panel traps for monitoring female grape berry moth.

Asunto(s)

RESUMEN

Coordinated sexual communication systems, seen in many species of moths, are hypothesized to be under strong stabilizing natural selection. Stabilized communication systems should be resistant to change, but there are examples of species/populations that show great diversification. A possible solution is that it is directional sexual selection on variation in male response that drives evolution. We tested a component of this model by asking whether 'rare' males (ca. 5 % of all males in a population) of the European corn borer moth (ECB), Ostrinia nubilalis, that respond to the sex pheromones of both ECB and a different Ostrinia species (O. furnacalis, the Asian corn borer, ACB), might play an important role in diversification. We specifically tested, via artificial selection, whether this broad male response has an evolvable genetic component. We increased the frequency of broad male response from 5 to 70 % in 19 generations, showing that broad-responding males could be important for the evolution of novel communication systems in ECB. We did not find a broader range of mating acceptance of broad males by females of the base population, however, suggesting that broad response would be unlikely to increase in frequency without the involvement of other factors. However, we found that ECB selection-line females accepted a broader range of courting males, including those of ACB, than did females of the base population. Thus, a genetic correlation exists between broad, long-range response to female sex pheromone and the breadth of female acceptance of males at close range. These results are discussed in the context of evolution of novel communication systems in Ostrinia.

Asunto(s)

RESUMEN

We investigated the role that the ratio and concentration of ubiquitous plant volatiles play in providing host specificity for the diet specialist grape berry moth Paralobesia viteana (Clemens) in the process of locating its primary host plant Vitis sp. In the first flight tunnel experiment, using a previously identified attractive blend with seven common but essential components ("optimized blend"), we found that doubling the amount of six compounds singly [(E)- & (Z)-linalool oxides, nonanal, decanal, ß-caryophyllene, or germacrene-D], while keeping the concentration of other compounds constant, significantly reduced female attraction (average 76% full and 59% partial upwind flight reduction) to the synthetic blends. However, doubling (E)-4,8-dimethyl 1,3,7-nonatriene had no effect on female response. In the second experiment, we manipulated the volatile profile more naturally by exposing clonal grapevines to Japanese beetle feeding. In the flight tunnel, foliar damage significantly reduced female landing on grape shoots by 72% and full upwind flight by 24%. The reduction was associated with two changes: (1) more than a two-fold increase in total amount of the seven essential volatile compounds, and (2) changes in their relative ratios. Compared to the optimized blend, synthetic blends mimicking the volatile ratio emitted by damaged grapevines resulted in an average of 87% and 32% reduction in full and partial upwind orientation, respectively, and the level of reduction was similar at both high and low doses. Taken together, these results demonstrate that the specificity of a ubiquitous volatile blend is determined, in part, by the ratio of key volatile compounds for this diet specialist. However, P. viteana was also able to accommodate significant variation in the ratio of some compounds as well as the concentration of the overall mixture. Such plasticity may be critical for phytophagous insects to successfully eavesdrop on variable host plant volatile signals.

Asunto(s)

RESUMEN

For some Lepidopteran pests, such as the grape berry moth Paralobesia viteana (Clemens), poor correlation between males captured in traps baited with sex pheromone and oviposition activities of female moths has called into question the value of pheromone-based monitoring for these species. As an alternative, we compared the capture of female and male grape berry moth in panel traps baited with synthetic host volatiles with captures of males in pheromone-baited wing traps over two growing seasons in two blocks of grapes in a commercial vineyard in central New York. Lures formulated in hexane to release either 7-component or 13-component host volatile blends captured significantly more male and female grape berry moth on panel traps compared with the numbers captured on panel traps with hexane-only lures. For both sexes over both years, the same or more moths were captured in panel traps along the forest edge compared with the vineyard edge early in the season but this pattern was reversed by mid-season. Male moths captured in pheromone-baited wing traps also displayed this temporal shift in location. There was a significant positive correlation between captured males and females on panel traps although not between females captured on panel traps and males captured in pheromone-baited traps for both years suggesting pheromone traps do not accurately reflect either female or male activity. Male moths captured in pheromone traps indicated a large peak early in each season corresponding to first flight followed by lower and variable numbers that did not clearly indicate second and third flights. Panel trap data, combining males and females, indicated three distinct flights, with some overlap between the second and third flights. Peak numbers of moths captured on panel traps matched well with predictions of a temperature-based phenology model, especially in 2008. Although effective, panel traps baited with synthetic host lures were time consuming to deploy and maintain and captured relatively few moths making them impractical, in the current design, for commercial purposes.

Asunto(s)

RESUMEN

First generation hybrid males from crosses between the Asian corn borer (ACB), Ostrinia furnacalis, and the "univoltine Z-strain" European corn borer (ECB), Ostrinia nubilalis, were examined with respect to behavioral and physiological responses to ACB and ECB pheromones. The hybrid males often flew to the pheromone of ECB Z-strain, but very rarely to the ACB pheromone. We mapped the tuning profiles of each ORN of the F(1) hybrids with respect to the relevant pheromone components and a common behavioral antagonist by employing differential cross-adaptation and varying doses of the ligands. In the trichoid sensilla of F(1) hybrid males, the three co-compartmentalized ORNs produced spikes that were very difficult to distinguish by size, unlike the parental populations. Comparing the responses to ACB and ECB components at different doses reveals overlapping profiles similar to males of both parental types, but more responsiveness to the ECB pheromone components. We were unable to detect any differences in the ORN tuning profiles when comparing males with different behavioral phenotypes. While the two ECB pheromone races have similar ORN tuning properties that are different from those in ACB, the spike-amplitude patterns of ECB E-strain and ACB have greater homology when compared to ECB Z-strain.

Asunto(s)

RESUMEN

The sex pheromone of Phyllophaga (Phytalus) georgiana was characterized as valine methyl ester, tentatively the L-enantiomer. This is the first sex pheromone identified from the Phyllophaga subgenus Phytalus. The pheromone was extracted from female glands, the active component isolated by coupled gas chromatography-electroantennogram detection analysis, characterized by mass spectrometry, and shown to be active in field tests. The seasonal flight pattern was determined for P. georgiana as well as for three other species, P. anxia (both northern and southern genitalic forms), P. gracilis, and P. postrema. The latter three species were captured in traps baited with L-isoleucine methyl ester.

Asunto(s)

RESUMEN

Recent studies have shown that flies from sympatric populations of Rhagoletis pomonella infesting hawthorn, apple, and flowering dogwood fruit can distinguish among unique volatile blends identified from each host. Analysis of peripheral chemoreception in Rhagoletis flies suggests that changes in receptor specificity and/or receptor neuron sensitivity could impact olfactory preference among the host populations and their hybrids. In an attempt to validate these claims, we have combined flight tunnel analyses and single sensillum electrophysiology in F(2) and backcross hybrids displaying a variety of behavioral phenotypes. Results show that differences in peripheral chemoreception among second-generation adults do not provide a direct correlation between peripheral coding and olfactory behavior. We conclude that either the plasticity of the central nervous system in Rhagoletis can compensate for significant alterations in peripheral coding or that peripheral changes present subtle effects on behavior not easily detectable with current techniques. The results of this study imply that the basis for olfactory behavior in Rhagoletis has a complicated genetic and neuronal basis, even for populations with a recent divergence in preference.

Asunto(s)

RESUMEN

Solid-phase microextraction (SPME) and gas chromatography coupled with electroantennographic detection (GC-EAD) were used to identify volatile compounds from shoots of riverbank grape (Vitis riparia) that attract the female grape berry moth (GBM, Paralobesia viteana). Consistent EAD activity was obtained for 11 chemicals: (Z)-3-hexen-1-yl acetate, (E)-linalool oxide, (Z)-linalool oxide, nonanal, linalool, (E)-4,8-dimethyl-1,3,7-nonatriene, methyl salicylate, decanal, beta-caryophyllene, germacrene-D, and alpha-farnesene. In flight-tunnel tests that involved female GBM and rubber septa loaded with subsets of these 11 compounds, we found that both the 11-component blend and a seven-component blend, composed of (E)-linalool oxide, (Z)-linalool oxide, nonanal, (E)-4,8-dimethyl-1,3,7-nonatriene, decanal, beta-caryophyllene and germacrene-D, elicited equivalent levels of upwind flight as freshly cut grape shoots. The removal of any of the seven compounds from the seven-component blend resulted in a significant decrease in female upwind flight responses. In a field trial with these two synthetic blends, traps equipped with either blend captured more female GBM compared to traps baited with hexane only (control), although the number of females caught was generally low. There were no differences in the number of males captured among treatments. Although in flight-tunnel trials, moths readily flew upwind to both grape shoots and rubber septa loaded with the best lures, they landed on shoots but not on rubber septa. Coupled with relatively low field catches, this suggests that additional host finding cues need to be identified to improve trap efficacy.

Asunto(s)

RESUMEN

The olfactory receptor neuron (ORN) and behavioral responses of hybrids between the Asian corn borer (ACB), Ostrinia furnacalis, and the E-strain European corn borer (ECB(E)), Ostrinia nubilalis were examined and compared to the parental populations. In hybrids and both parents, the large-spike-size ORN was capable of responding to all four pheromone components of ACB and ECB, despite differences in which compounds elicited the greatest spike frequency in each population. There was a small-spiking ORN more narrowly tuned to the minor pheromone components in both ACB and ECB(E). In hybrids the homologous small-spiking ORN was tuned primarily to the ECB(E) minor pheromone component, with some responsiveness to the ACB minor component. Both species and all the hybrids had an intermediate spike-size ORN tuned primarily to their common behavioral antagonist. Dominance of responsiveness to the ECB(E) versus the ACB minor pheromone component on the small-spiking ORN may explain the greater tendency of hybrids to fly upwind to the ECB(E) pheromone blend than the ACB blend. This finding points toward a distinct evolutionary role for this ORN in allowing a pheromone shift.

Asunto(s)

RESUMEN

We combine the use of labeled precursors with enzyme inhibitors to decipher the biosynthetic pathway of pheromone biosynthesis and the rate-limiting step/s that are regulated by pheromone biosynthesis activating neuropeptide (PBAN). We demonstrate that Plodia interpunctella is able to utilize hexadecanoic acid, and to a lesser extent tetradecanoic acid, for the biosynthesis of the main pheromone component (Z,E)-9,12-tetradecadienyl acetate. This indicated that the main pathway involves a Delta11 desaturase, chain shortening, followed by a Delta12 desaturase, but that a functional Delta9 desaturase could also be utilized. Using reverse transcription-quantitative real-time polymerase chain reaction (RT-QPCR) we distinguish two out of nine possible desaturase gene transcripts in P. interpunctella that are expressed at the highest levels. The rate-limiting step for PBAN-stimulation was studied in two moth species so as to compare the biosynthesis of a diene (P. interpunctella) and a monoene (Helicoverpa armigera) main pheromone component. In both species, incorporation of label from the (13)C sodium acetate precursor was activated by PBAN whereas no stimulatory action was observed in the incorporation of the precursors: (13)C malonyl coenzyme A; hexadecanoic 16,16,16-(2)H(3) or tetradecanoic 14,14,14-(2)H(3) acids. The acetyl coenzyme A carboxylase (ACCase) inhibitor, Tralkoxydim, inhibited the PBAN-stimulation of incorporation of stable isotope whereas the fatty-acyl reductase inhibitor, Mevastatin, failed to influence the stimulatory action of PBAN. These results provide irrefutable support to the hypothesis that PBAN affects the production of malonyl coenzyme A from acetate by the action of ACCase in the pheromone glands of these moths.

Asunto(s)

RESUMEN

Semiochemicals play important roles in mate and host recognition of herbivorous insects, such as moths, and flight tunnels have been an effective tool in the identification of these bioactive compounds. However, more work has been carried out on pheromones than on host plant cues, and few examples exist where flight tunnel evaluations of host cues have resulted in a lure that is attractive under field conditions. Our goal was to determine whether the flight tunnel could be used to evaluate the response of a specialist moth, grape berry moth (GBM), to its host plant (grapevines), by incorporating ecological and physiological aspects of GBM biology. We found grape shoot tips and mature leaves were more attractive to female GBM than unripe and ripe berries or flowers. Under optimized flight tunnel conditions, approximately 80% of tested females flew upwind and closely approached or landed on the most preferred target. Mating status, wind speed, the time of day, and the presence/absence of patterns that resemble grape tissues on the top of the flight tunnel all significantly affected the responses of female GBM. Consideration of these factors in flight tunnel assays will aid in the development of a synthetic lure that can be used to monitor female moths in the field.

Asunto(s)

RESUMEN

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 captures.

Asunto(s)

RESUMEN

Three percent of E-strain Ostrinia nubilalis males fly upwind in response to the Ostrinia furnacalis pheromone blend [a 40:60 ratio of (E)-12-tetradecenyl acetate to (Z)-12-tetradecenyl acetate (E12-14:OAc to Z12-14:OAc)], in addition to their own pheromone blend [a 99:1 ratio of (E)-11-tetradecenyl acetate to (Z)-11-tetradecenyl acetate) (E11-14:OAc to Z11-14:OAc)]. We assessed the olfactory receptor neuron (ORN) responses of these behaviorally "rare" males versus those of normal males. For the three ORNs housed within each sensillum, we tested responsiveness to Z12-14:OAc, E12-14:OAc, Z11-14:OAc, E11-14:OAc, and the behavioral antagonist (Z)-9-tetradecenyl acetate (Z9-14:OAc). Z11-14:OAc, E11-14:OAc, and Z9-14:OAc stimulated ORNs exhibiting distinct small, large, and medium spike sizes, respectively. For rare and normal males, both Z12-14:OAc and E12-14:OAc usually elicited responses from the largest-spiking ORN. In many ORNs of normal males, Z12-14:OAc or E12-14:OAc stimulated the smaller-spiking ORN that is responsive to Z11-14:OAc. In rare males, detectable ORN responses from the smaller-spiking ORN in response to Z12- and E12-14:OAc were virtually non-existent. These differences in ORN tuning in rare males will tend to create an ORN firing ratio between the large- and small-spiking ORNs in response to the O. furnacalis blend that is similar to that elicited by the O. nubilalis blend.

Asunto(s)

RESUMEN

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 compounds.

Asunto(s)

RESUMEN

The biosynthesis of female moth sex pheromone blends is controlled by a number of different enzymes, many of which are encoded by members of multigene families. One such multigene family, the acyl-CoA desaturases, is composed of certain genes that function as key players in moth sex pheromone biosynthesis. Although much is known regarding the function of some of these genes, very little is known regarding how novel genes have evolved within this family and how this might impact the establishment of new sex pheromone blends within a species. We have discovered that several cryptic Delta11 and Delta14 desaturase genes exist in the genomes of the European and Asian corn borers (Ostrinia nubilalis and Ostrinia furnacalis, respectively). Furthermore, an entirely novel class of desaturase gene has arisen in the Ostrinia lineage and is derived from duplication of the Delta11 desaturase gene and subsequent fusion with a retroposon. Interestingly, the genes have been maintained over relatively long evolutionary time periods in corn borer genomes, and they have not been recognizably pseudogenized, suggesting that they maintain functional integrity. The existence of cryptic desaturase genes in moth genomes indicates that the evolution of moth sex pheromone desaturases in general is much more complex than previously recognized.

Asunto(s)

RESUMEN

Olfactory receptor neuron (ORN) response was measured to assess why some males ("rare males") of the Asian corn borer (ACB), Ostrinia furnacalis, have a broad behavioral response to fly upwind to both the ACB and the European corn borer (ECB), Ostrinia nubilalis, pheromone blends. We performed single-sensillum electrophysiological recordings on ACB males that had been behaviorally assessed for upwind flight response to the ACB blend [60:40 (Z)-12-tetradecenyl acetate (Z12-14:OAc) to (E)-12-tetradecenyl acetate (E12-14:OAc)], as well as to ECB (Z-strain) and ECB (E-strain) blends [3:97 and 99:1 (Z)-11-tetradecenyl acetate (Z11-14:OAc) to (E)-11-tetradecenyl acetate (E11-14:OAc)]. Sensilla from all types of males had large- and small-spike-sized ORNs responding strongly to Z12- or E12-14:OAc, but weakly to Z11- and E11-14:OAc. In the majority of males ("normal males") that flew upwind only to the ACB blend, Z11-14:OAc elicited responses in an intermediate spike-sized ORN associated with behavioral antagonism that is mainly tuned to (Z)-9-tetradecenyl acetate (Z9-14:OAc). In the rare-type ACB males that flew to both the ACB and ECB pheromone blends, Z11-14:OAc did not stimulate this ORN. Increased responsiveness to ancestral pheromone components by ORNs associated with behavioral antagonism could be instrumental in reproductive character displacement, or in reinforcement and reproductive isolation during speciation by helping to increase assortative mating between males and females in derived populations that use novel sex pheromone blends.

Asunto(s)

RESUMEN

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 100 microg 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 races.

Asunto(s)

RESUMEN

The Rhagoletis pomonella species complex is one of the foremost examples supporting the occurrence of sympatric speciation. A recent study found that reciprocal F(1) hybrid offspring from different host plant-infesting populations in the complex displayed significantly reduced olfactory host preference in flight-tunnel assays. Behavioral and electrophysiological studies indicate that olfactory cues from host fruit are important chemosensory signals for flies to locate fruit for mating and oviposition. The reduced olfactory abilities of hybrids could therefore constitute a significant post-mating barrier to gene flow among fly populations. The present study investigated the source of changes in the hybrid olfactory system by examining peripheral chemoreception in F(1) hybrid flies, using behaviorally relevant volatiles from the parent host fruit. Single-sensillum electrophysiological analyses revealed significant changes in olfactory receptor neuron (ORN) response specificities in hybrid flies when compared to parent ORN responses. We report that flies from F(1) crosses of apple-, hawthorn- and flowering dogwood-origin populations of R. pomonella exhibited distinct ORN response profiles absent from any parent population. These peripheral alterations in ORN response profiles could result from misexpression of multiple receptors in hybrid neurons as a function of genomic incompatibilities in receptor-gene pathways in parent populations. We conclude that these changes in peripheral chemoreception could impact olfactory host preference and contribute directly to reproductive isolation in the Rhagoletis complex, or could be genetically coupled to other host-associated traits.

Asunto(s)