Roles of minor components in pheromone-mediated behavior of western spruce budworm male moths

The behavior of male western spruce budworm moths,Choristoneura occidentalis Freeman, was observed in a flight tunnel in response to virgin females and synthetic sex pheromone components, alone and in blends. Pheromone blends were also compared in the field using sticky trap bioassays. Pheromones were incorporated into small rods of polyvinyl chloride. The blend of 928 (E/Z)-11-tetradecenal-8911 (E/Z)-11-tetradecenyl acetate-8515 (E/Z)-11-tetradecenol (AldAcOH) that approximated that released from a virgin female moth elicited levels of response similar to those elicited by the female. This blend induced a significantly greater percentage of moths to fly upwind and land at the lure than did the Ald lure. In contrast to the flight-tunnel bioassays, the numbers of moths caught in Ald-baited sticky traps in the field were not significantly increased by the addition of Ac and OH lures. The net upwind groundspeed of flight in response to the 0.05% Ald lure was lower than that in response to the virgin females and was significantly increased by the addition of Ac + OH lures in two of three bioassays. The flight-tunnel bioassays support the hypothesis that the natural blend of major (Ald) and minor (Ac + OH) components stimulates the precopulatory behavior of western spruce budworm male moths at long range (> 1 m downwind) as well as at close range.     

Effect of Wind Speed on the Pheromone-Mediated Behavior of Sexual Morphs of the Potato Aphid, Macrosiphum euphorbiae (Thomas) Under Laboratory and Field Conditions

The effect of wind on the potato aphid, Macrosiphum euphorbiae, male responsiveness to the sex pheromone, and on the calling behavior of virgin oviparae, was studied under constant wind speeds in the laboratory and in the field. A significant proportion of females called at wind speeds up to 4 m/sec, whereas male flight behavior in clean air was inhibited at velocities > 2 m/sec. However, males continued to walk over the range of wind speeds at which females called. Under constant wind velocities in a wind tunnel, males downwind of calling females oriented on the upwind edge of the release stand, and fewer individuals took flight at low constant wind speeds than in a clean air plume. In all cases, whether calling females were present or not, the males that took flight moved downwind. However, when a bridge was available, a significant proportion of males walked upwind to the pheromone source. The same orientation and walking behaviors were observed when males were placed downwind of calling females under variable wind conditions in the field. However, contrary to the laboratory results, 30% of the males tested flew upwind and landed on the source. A more detailed examination found that males orienting toward a source would walk if wind speeds were high but initiated flight in an “upwind” direction if there was a lull in wind velocity. These findings suggest that for the potato aphid, and probably for many other insect species with weak flight capacity, walking behavior is a significant component of pheromone-mediated mate location. This would permit males to continue foraging for calling females in the vicinity when wind velocities inhibit flight.     

Spruce budworm (Choristoneura fumiferana) pheromone chemistry and behavioral responses to pheromone components and analogs

This paper reviews the sex pheromone chemistry and pheromone-mediated behavior of the spruce budworm and related coniferophagous (Choristoneura) budworms. InC. fumiferana, temporal changes in pheromone-gland monounsaturated fatty acids (pheromone precursors) enable the prediction of the primary sex pheromone components. This technique may also be applicable for predicting additional pheromone components. Tetradecanal (14 Ald), previously shown to enhance close-range precopulatory behavior, lowers the threshold of response by males for upwind flight to a pheromone-component source. Spruce budworm males maintain upwind flight to 955 (E/Z)-1,12-pentadecadiene (diolefin analog) after initiating upwind flight to a primary-component pheromone source (955E/Z11-14Ald). This is the first demonstration of apparently normal male flight responses to a pheromone analog.Lepidoptera: Tortricidae     

Flight Tunnel Responses of Female Grape Berry Moth (<Emphasis Type="Italic">Paralobesia viteana</Emphasis>) to Host Plants

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.     

Male moth sensitivity to multicomponent pheromones: Critical role of female-released blend in determining the functional role of components and active space of the pheromone

In the present study male redbanded leafroller (Argyrotaenia velutinana), cabbage looper (Trichoplusia ni), and Oriental fruit moths, (Grapholita molesta), were tested in a flight tunnel to (1) the major pheromone component, (2) theZ/E pheromone component mixtures for Oriental fruit moth and redbanded leafroller, (3) and the female-released blends, over a series of dosages. Experiments were designed to test the hypothesis that male response downwind of a female is initiated by the major component and that minor components function only to elicit behaviors close to the female during close-range approach and courtship. The results did not support this hypothesis, but rather showed that males initiated upwind flight in significantly higher percentages to the complete blends of components, at all dosages, compared to single components or partial blends. Addition of minor components also signficantly enhanced male perception of the major component at lower dosages, resulting in completed flights to dosages of the major component that alone did not elicit any upwind flight. Our results support the concept that minor components function to enhance male sensitivity to the pheromone, and the specificity of the signal. Our results also support the hypothesis that the active space of the pheromone is a function of the upper and lower concentration thresholds for the blend of components, and not simply for the major component.     

Pheromone emission and blend percentages inEoreuma loftini determined by two methods

Calling behavior and pheromone emission by virgin femaleE. loftini moths were investigated in laboratory experiments. Calling peaked during the last three hours of the night. Three-day-old moths called more than older or younger moths and began calling earlier in the night than younger moths. Female emissions were collected in flasks without airflow and cylinders with airflow. Control tests indicated that the pheromone components (Z)-11-hexadecenyl acetate (HDA) and (Z)-13-octadecenylacetate (ODA) were 69 and 54% adsorbed on moths, respectively, and the component (Z)-13-octadecenal (ODL) was 92–99% adsorbed depending on its concentration, when put into flasks with noncalling females for 4 hr. Pheromone exposed to moths for less than 4 hr was adsorbed less. After correction for adsorption, the pheromone blend from females calling in flasks was 9:42:49% of HDA/ODL/ODA with an overall emission rate of 58 ng/female/4 hr. Three-day-old females emitted more pheromone than 0- to 2- or 4- to 5-day-old moths, in flasks. Little or no pheromone put into cylinders either downwind or upwind from a male moth was adsorbed by the moth. The pheromone blends from females calling in cylinders, corrected using downwind and upwind control test results, respectively, were 15:35:50 and 13:40:48% of HDA/ODL/ODA with overall emission rates of 32 and 35 ng/female/night.Lepidoptera: Pyralidae.     

Specificity of male response to multicomponent pheromones in noctuid mothsTrichoplusia ni andPseudoplusia includens

The response of male cabbage looper (CL) and soybean iooper (SBL) moths was observed in the flight tunnel and measured in field tests to the six-component CL pheromone, the five-component SBL pheromone, and toZ7–12: OAc, the major component common to each pheromone. In both the flight tunnel and the field, male CL exhibited significantly greater levels of response to their six-component blend than toZ7–12: OAc alone. A low level of cross-attraction of male CL to the SBL pheromone was observed in both the flight tunnel and the field, but it was quantitatively and qualitatively similar to their response toZ7–12: OAc alone. Thus the minor components of the SBL blend did not appear to disrupt the flight behavior of male CL. With respect to SBL, in the flight tunnel males also exhibited a greater level of response to the five-component blend compared toZ7–12: OAc, but in the field their response was not significantly different to either treatment. There was also a low level of cross-attraction of male SBL to the CL blend, but this appeared to involve a significant arrestment effect on the upwind flight of males, as well as a difference in male sensitivity to the blend of components compared withZ7–12: OAc alone. The observed arrestment effect may have been due to male perception of one or more minor components of the CL pheromone. The results show that the multicomponent pheromones of these species function effectively as specific mating signals and that discrimination of odor quality by male moths can occur as the result of minor components affecting male sensitivity or their upwind flight response to the pheromone.     

Sex pheromone-mediated flight and landing behaviors of the European corn borer,Ostrinia nubilalis (Hübner)

The pheromone-mediated flight and landing behaviors of maleOstrinia nubilalis were studied in a wind tunnel. The pheromone source was placed in the middle of an 18 × 18-cm horizontal surface, and a smaller surface placed 4, 18, or 36 cm downwind. The smaller surface did not appear to affect significantly the flight tracks or position of landing of males on the upwind surface, and it allowed the positions and altitudes of males as they passed over the downwind surface to be estimated. The flight altitude and position of males as they passed over the downwind surface related to where males landed on the upwind surface. Regardless of the downwind position of the downwind surface, most males flew over its center (i.e., in line with the source) and landed in line with the source on the upwind surface. When a small 2.5 × 10-cm vertical object was placed on the upwind surface, just upwind and to one side of the source, males flew over the downwind surface in positions skewed toward the vertical object and in broader distributions than for the comparable situation without an object: males landed on the upwind surface on positions skewed toward, or on, the object and with a broader distribution (laterally). Flight altitude also corresponded with landing position. Thus, when there was no vertical object, most males flew just above the downwind surface and landed on the downwind edge of the upwind surface. In contrast, with the vertical object, males flew significantly higher and tended to land past the downwind edge of the upwind surface. With a taller object (20 cm), males flew even higher, past the downwind edge and most landed on the vertical object. These data show the close relationship between flight and landing behaviors of maleO. nubilalis and suggest that flight maneuvers that determine track and altitude largely govern where a male lands.     

Wind tunnel studies of sex pheromone-mediated behavior of the Hessian fly (Diptera: Cecidomyiidae)

In a wind-tunnel, male Hessian flies flying toward a source of the female-produced sex pheromone exhibited flight maneuvers very similar to those described for male moths. Upwind flight, consisting of zigzagging and straight flight upwind, was initiated within seconds after flies were placed in the odor plume. This upwind flight was sometimes interrupted by casting, which consisted of wide excursions in the horizontal plane ranging 10–35 cm across the central zone of the tunnel. Comparison of the flight maneuvers of males exposed to ten female equivalents of a hexane extract of female ovipositors and males exposed to 20 ng of (2S)-(E)10-tridecen-2-yl acetate (SE10-13:OAc), which has been identified as a component of the Hessian fly sex pheromone, indicated that the sex pheromone probably contains additional components. However, SE10-13: OAc elicited upwind flight and source location by a significant number of males, even at dosages as low as 2 ng on filter paper. At the highest dosage of SE10-13:OAc tested (200 ng on filter paper), there was a significant decrease in net flight velocity and a slight, but not significant, reduction in the number of males contacting the odor source. The addition of increasing amounts of the R enantiomer to the S enantiomer resulted in increased inhibition of upwind flight and source contact by males.     

Disruption of male spruce budworm orientation to calling females in a wind tunnel by synthetic pheromone

Male spruce budworm [Chorisloneura fumiferana (Clem.)] moths were held for 3 hr in a wind tunnel and subjected to various concentrations of background synthetic pheromone. They were then exposed to calling females and their response was recorded. The background pheromone was presented either as discrete turbulent plumes or as a uniform permeation throughout the tunnel. The numbers of males wing-fanning and flying in response to the calling females decreased as the concentration of background pheromone increased. Of the males which flew, a higher proportion progressed upwind in the discrete plumes than in the uniform permeation, an indication that structure in the pheromone cloud is necessary for upwind progression. In both discrete plumes and uniform permeation fewer males were able to locate the females (i.e., disruption was greater) as the concentration of synthetic pheromone increased, but for the same total release rates, disruption was greater when the synthetic pheromone was released in discrete plumes rather than in a uniform permeation. This implies that disruption which involves luring males to sources of synthetic pheromone is more effective than masking female plumes by uniform permeation and suggests that it is more efficient to release pheromone from a few potent sources than from numerous low-potency sources.     

Identification of Sex Pheromone Components of the Box Tree Pyralid,Glyphodes perspectalis

Analysis of ovipositor extracts of the box tree pyralid, Glyphodes perspectalis (Lepidoptera: Crambidae), by coupled gas chromatography-electroantennogram detection and gas chromatography yielded three candidate pheromone compounds. Gas chromatography-mass spectrometry, and reaction with dimethyl disulfide (DMDS), identified these compounds as (Z)-11-hexadecenal (Z11-16:Ald), (E)-11-hexadecenal (E11-16:Ald), and (Z)-11-hexadecenol (Z11-16:OH). The ratio of these three compounds in crude extract was 5:1.25:1, and the total amount was approximately 100 ng/female. In laboratory bioassays, Z11-16:Ald alone was attractive to males. In field bioassays, however, Z11-16:Ald alone was not attractive to males, but a mixture of Z11-16:Ald and E11-16:Ald was. The addition of Z11-16:OH to the two aldehydes, significantly reduced attractiveness to male moths in a field trial. From these results, we conclude that the aldehyde compounds comprise the sex pheromone components of G. perspectalis. A rubber septum containing 0.6 mg of the two aldehydes at the natural ratio was an effective lure for monitoring this pest.     

Spatial discrimination between sources of pheromone and an inhibitor by the light-brown apple mothEpiphyas postvittana (Walker) (Lepidoptera: Tortricidae)

Inhibition of the behavioral responses of maleEpiphyas postvittana moths by theZ isorner of the major component of the sex pheromone,E11-14: OAc, was studied in a wind tunnel. Inhibition was detectable at a Z isomer concentration of 10% that of the major component and was greatest when it was added to the same source as the pheromone. Inhibition declined rapidly as the inhibitor was moved across-wind away from the pheromone source but was largely maintained when the sources were separated upwind or downwind. The results showed that the insects possess a high degree of temporal resolution for odor plumes of different composition.     

Pheromone Antagonism in the European Corn Borer Moth Ostrinia nubilalis

Mixing the sex pheromones of the Mediterranean corn borer, Sesamia nonagrioides, and the European corn borer, Ostrinia nubilalis, results in significantly lower captures of O. nubilalis when compared to traps loaded with its pheromone alone. Rubber septa loaded with a constant concentration of the pheromone of O. nubilalis and different percentages of the S. nonagrioides pheromone (from 1 to 100%) causes dose-dependent antagonism in the field. Electroantennograms of O. nubilalis males showed high antennal responses to its own pheromone components, followed by smaller responses to the major, [(Z)-11-hexadecenyl acetate (Z11-16:Ac)], and two minor components [dodecyl acetate (12:Ac) and (Z)-11-hexadecenal (Z11-16:Ald)] of the S. nonagrioides pheromone. There was almost no response to the S. nonagrioides minor component (Z)-11-hexadecenol (Z11-16:OH). Field tests that used traps baited with the O. nubilalis pheromone plus individual components of S. nonagrioides showed that Z11-16:Ald causes the antagonism. Adding 1% Z11-16:Ald to the pheromone of O. nubilalis reduced oriented flight and pheromone source contact in the wind tunnel by 26% and 83%, respectively, and trap captures in the field by 90%. The other three pheromone components of S. nonagrioides inhibited pheromone source contact but not oriented flight of O. nubilalis males and did not inhibit capture in the field. Cross-adaptation electroantennogram suggests that Z11-16:Ald stimulates a different odor receptor neuron than the pheromone components of O. nubilalis. We conclude that Z11-16:Ald is a potent antagonist of the behavioral response of O. nubilalis.     

Interspecific Pheromone Plume Interference Among Sympatric Heliothine Moths: A Wind Tunnel Test Using Live, Calling Females

Three species of North American heliothine moths were used to determine the level at which interspecific female interference of male attraction to conspecific females occurs. We used live calling females of Heliothis virescens, H. subflexa, and Helicoverpa zea, as lures for conspecific males in a wind tunnel, and then placed heterospecific females on either side of the original species such that the plumes of the three females overlapped downwind. In nearly all combinations, in the presence of heterospecific females, fewer males flew upwind and contacted or courted the source than when only conspecific females were used in the same spatial arrangement. Males did not initiate upwind flight to solely heterospecific female arrangements. Our results show that the naturally emitted pheromone plumes from heterospecific females of these three species can interfere with the ability of females to attract conspecific males when multiple females are in close proximity. However, the fact that some males still located their calling, conspecific females attests to the ability of these male moths to discriminate point source odors by processing the conflicting information from interleaved strands of attractive and antagonistic odor filaments on a split-second basis.     

More Rare Males in <Emphasis Type="Italic">Ostrinia</Emphasis>: 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 100 μg 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.     

Disruption of male oriental fruit moth to calling females in a wind tunnel by different concentrations of synthetic pheromone

Disruption of male Oriental fruit moth orientation to calling females was studied in a wind tunnel by surrounding calling female moths with septa loaded with synthetic pheromone. At the lowest loadings, 0.01 and 0.1µg, which produced release rates well below those of calling females, some males flew to septa instead of the females. At loadings of 1 and 10µg, which produced release rates close to those of a calling female, more than half the males flew to septa instead of the females, but there was little evidence of habituation at any of these loadings. At higher loadings, 100 and 1000µg, upwind flight of males was arrested, and many males remained inactive, indicating habituation. Preexposure of the males for 3 hr to ambient pheromone concentrations in the tunnel had no significant effect on numbers of disrupted males. However, at the 1000-µg loading, most of the males that had been preexposed to the synthetic pheromone remained inactive. This may indicate a higher level of habituation than among males that had not been preexposed, most of which flew, although they subsequently showed flight arrestment. Levels of disruption were similar to those found for the spruce budworm in comparable experiments. In both species, less than 1% of the males were able to locate females when time-averaged concentrations of synthetic pheromone were above 20 ng/m³. However, levels of inactivity and flight arrestment were higher among male Oriental fruit moths than among male spruce budworms, which may explain why Oriental fruit moths are more susceptible to disruption than are spruce budworms.     

Attraction of male spruce budworm moths,Choristoneura fumiferana (Clemens), to pheromone-baited traps in small-tree thinnings

Mean catches of spruce budworm,Choristoneura fumiferana (Clemens), moths were not significantly different among four small-tree thinning treatments of young spruce-fir-hemlock regeneration. Significant inverse relationships were found between trap catches and distances to nearby spruce-fir-hemlock overstory. Prevailing wind directions indicated that moths were attracted anemotactically to upwind pheromone sources. No definite trends were detected between catches and temperature or precipitation.Lepidoptera: Tortricidae.A contribution to the Canada/ United States (CANUSA) Spruce Budworms Program. Mention of proprietary products does not constitute an endorsement of those products by the USDA.     

Comparison of sex pheromone composition and pheromone-mediated male behavior of laboratory-reared and wildHeliothis zea (Lepidoptera: Noctuidae)

Analysis of ovipositor extracts of lab-reared (> 120 generations) and wildHeliothis zea indicated small but significant differences in the percent composition of the four aldehyde components of the sex pheromone. (Z)-11-hexadecen-1-ol (Z11–16OH) was present in both populations and amounted to only 2.8% of the total pheromone. There was no significant difference in four of the six behavioral categories between lab-reared and wild males exposed to the four-component sex pheromone in the flight tunnel. Ninety and 84% males flew to the pheromone source, respectively. However, with the addition ofZ11–16OH to the pheromone blend, none of the wild males flew upwind to the stimulus source, whereas 36% of the lab-reared males completed the flight. It is suggested that prolonged inbreeding in closed quarters rendered these males less discriminating to qualitative differences in a pheromone blend.     

Filamentous nature of pheromone plumes protects integrity of signal from background chemical noise in cabbage looper moth,Trichoplusia ni

(Z)-7-Dodecenol failed to interrupt pheromone-mediated anemotactic responses by male cabbage looper moths,Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae) in a wind tunnel when released 5 cm crosswind on both sides of the pheromone source or 10 cm upwind of the source to create an overlapping plume downwind. Significant inhibitory effects of (Z)-7-dodecenol were observed when released with the six-component pheromone blend from the same septum or abutting septa. These results indicate that (Z)-7-dodecenol needs to be received simultaneously with the pheromone blend to inhibit the anemotactic responses of males to the sex pheromone. We suggest that this feature and the filamentous nature of pheromone plumes render pheromone signals relatively protected from background chemical noise that may originate from pheromone plumes of other insect species. Unless filaments from a pheromone signal and an inhibitor arrive simultaneously, the integrity of the signal is maintained.     

Evolution of behavioral responses to sex pheromone in mutant laboratory colonies ofTrichoplusia ni

Male cabbage looper moths,Trichoplusia ni, from two colonies in which all females express an abnormal sex pheromone production phenotype were evaluated in a laboratory wind tunnel for upwind flight responses to the normal and abnormal sex pheromones. The abnormal sex pheromone blend consisted of 20 times as much (Z)-9-tetradecenyl acetate and 30-fold less (Z)-5-dodecenyl acetate compared to the normal pheromone blend. Initially, these males exhibited poor behavioral responses to the abnormal sex pheromone and maximum responses to the normal pheromone blend, indicating that there was no linkage between signal production and response. After 49 generations of laboratory rearing, males from the mutant colonies maintained good responses to the normal pheromone and increased their behavioral response to the abnormal sex pheromone to the same levels as for the normal pheromone. Over the same period, normal males maintained their preference for the normal pheromone. These results indicated that evolution had occurred in mutant colonies in favor of greater male responsiveness to the abnormal sex pheromone, resulting in the broadening of the response spectrum to pheromone blend ratios. This evolution presumably resulted from a mating advantage to those males that did not discriminate against mutant-type females in the mutant colonies.