Pheromone Emission Rates Research Articles

Comparison of Attraction and Trapping Capabilities of Bucket- and Delta-Style Traps With Different Pheromone Emission Rates for Gypsy Moths (Lepidoptera: Erebidae): Implications for Understanding Range of Attraction and Utility in Surveillance.

Delta- and bucket-style (Universal or Unitrap) traps baited with 1 standard survey lure and 1/3 and 3 lures were compared for their attractiveness and trapping efficiencies for gypsy moth, Lymantria dispar L. (Lepidoptera: Erebidae), males. With bucket traps, the numbers of males attracted to within 2 m of traps and the proportion of these actually captured were identical among the three doses although the percentage of attracted males actually captured in bucket traps was low, less than 15%. A three-lure delta trap attracted about 70% more males than traps with the two lower doses. Capture efficiencies were above 80% for 1/3- and one-lure traps and about 60% for traps baited with three lures. The number of males captured in delta traps was equivalent for the three doses although our observations also suggest that a delta trap baited with three lures drew males from a wider range than lower dose lures and therefore would be a more sensitive trap for detecting incipient populations. We also noted that males tended to arrive in clusters, suggesting that attraction over moderate distances requires periods when the wind direction is fairly constant. This observation coupled with the great variability in the direction of male arrival to the traps also suggests that important changes in the area of influence of the plume are driven in such forested areas by slower but greater changes in wind direction compared with open habitats.

Optimizing the Point-Source Emission Rates and Geometries of Pheromone Mating Disruption Mega-Dispensers.

High-emission-rate "mega-dispensers" have come into increasing use for sex pheromone mating disruption of moth pests over the past two decades. These commercially available dispensers successfully suppress mating and reduce crop damage when they are deployed at very low to moderate densities, ranging from 1 to 5/ha to 100-1000/ha, depending on the dispenser types and their corresponding pheromone emission rates. Whereas traditionally the emission rates for successful commercial mating disruption formulations have been measured in terms of amounts (usually milligram) emitted by the disruptant application per acre or hectare per day, we suggest that emission rates should be measured on a per-dispenser per-minute basis. In addition we suggest, because of our knowledge concerning upwind flight of male moths being dependent on contact with pheromone plume strands, that more attention needs to be paid to optimizing the flux within plume strands that shear off of any mating disruption dispenser's surface. By measuring the emission rates on a per-minute basis and measuring the plume strand concentrations emanating from the dispensers, it may help improve the ability of the dispensers to initiate upwind flight from males and initiate their habituation to the pheromone farther downwind than can otherwise be achieved. In addition, by optimizing plume strand flux by paying attention to the geometries and compactness of mating disruption mega-dispensers may help reduce the cost of mega-dispenser disruption formulations by improving their behavioral efficacy while maintaining field longevity and using lower loading rates per dispenser.

Study on the Optimum Pheromone Release Rate for Attraction of <I>Chilo suppressalis</I> (Lepidoptera: Pyralidae)

Traditional chemical control against Chilo suppressalis Walker is currently being replaced in Spain by new methods based on pheromones. A key step to improve the efficacy of these methods is the determination of the optimum pheromone release rate, which is still uncertain for this pest. In this work, the pheromone release profile and the field performance of a new mesoporous dispenser was compared with a standard commercial dispenser. For this purpose, pheromone loads were extracted from field-aged dispensers and quantified by gas chromatography with flame ionization detector. In addition, a field trial was carried out with traps baited with one, two, or three mesoporous dispensers per trap, as well as with traps containing one standard dispenser. We found that the highest number of field catches did not correspond to the highest pheromone emission rate, which suggests a repellent effect of the insect if the emission is excessive. The results suggest that the attractant activity was maximized by emitting approximately 34 microg/d. The efficacy of the mesoporous dispenser and its possible improvements are discussed.

Aggregation pheromone of the cereal leaf beetle: field evaluation and emission from males in the laboratory.

The previously identified, male-specific compound of the cereal leaf beetle (CLB, Chrysomelidae; Oulema melanopus), (E)-8-hydroxy-6-methyl-6-octen-3-one, was studied further with respect to field activity and emission rate from male beetles. In a 5-week field experiment in Oregon, the compound was shown to function as an aggregation pheromone in attracting male and female CLBs migrating from overwintering sites in spring. Traps baited with the synthetic compound (500 microg per rubber septum) caught 3.3 times more CLBs than control traps. Lower doses of the pheromone (50 and 150 microg) were less attractive than the 500 microg dose. One relatively abundant, volatile compound from the host plant (oats), (Z)-3-hexenyl acetate, that elicited responses from beetle antennae was not attractive, either by itself or as a synergist of the pheromone. Both sexes were captured about equally for all treatments. We also measured daily pheromone emission by male beetles in the laboratory. Individual males feeding on oat seedlings under greenhouse conditions emitted as much as 6 microg per day, which is about 500 times higher than had been previously observed under incubator conditions. The pheromone emission rate was at least five times higher during the day than at night, and in one male, emission spanned a period of 28 d. The release rate of synthetic pheromone from the 500 microg septa was very similar to the maximum from single males; thus, future experiments should evaluate even higher doses. The field results indicate that the pheromone has potential as a monitoring tool for early detection of CLBs as they move from their overwintering sites into newly planted cereal crops in spring.

Mating Disruption of European Corn Borer, Ostrinia nubilalis by Using Two Types of Sex Pheromone Dispensers Deployed in Grassy Aggregation Sites in Iowa Cornfields

We investigated the potential of disrupting pheromone-mediated mating communication in European corn borer, Ostrinia nubilalis (Hübner). The female sex pheromone, a blend of (Z)-11-tetradecenyl acetate and ( E)-11-tetradecenyl acetate in a ratio of ∼97 : 3 was released from two dispenser types and in two deployment patterns, a Shin-Etsu rope formulation spaced 2 m apart and a widely-spaced (35 m) pattern using a controlled release system called the Metered Semiochemical Timed Release System (MSTRS TM). Both dispensers were situated in grassy sites that constitute aggregation areas for O. nubilalis mating activity within and around cornfields at three different locations in Iowa. Pheromone-emission rate (after 7 days in the field) from the MSTRS TM (6.09 μg/min) was ca. 26 times greater than from the rope formulation (0.23 μg/min). Both dispensers during both first and second flights achieved a significant level of disruption of pheromone-source location (averaging 97%). More importantly, a significant level of mating disruption was achieved, as measured by the frequency of mating by free-flying feral females. The mean number of matings, as measured by spermatophores, per first generation female was 1.33 in the MSTRS TM plots and 1.58 in the rope plots, compared with 1.88 in untreated check plots. During the second flight, the number of matings per female averaged 1.63 in the MSTRS TM plots, 1.56 in the rope plots and 2.17 in untreated check plots. There was also a significant reduction in the proportion of females that mated at least once during both flights in MSTRS TM plots. During the first flight, 17 and 10% fewer females mated in the MSTRS TM-treated and rope-treated fields, respectively. A similar level of disruption was also achieved during the second flight.

Does PBAN play an alternative role of controlling pheromone emission in the cabbage looper moth, Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae)?

There is an active process by which sex pheromone reserves of female cabbage looper moths, Trichoplusia ni, are transported to the gland's surface during the nocturnal period of calling. We hypothesized that this mobilization was controlled by a head factor, possibly related to the pheromone biosynthesis activating neuropeptides (PBAN) that in other species stimulate pheromone synthesis. We evaluated the impact of head extracts of T. ni on pheromone emission and glandular content of pheromone. During the photophase injected head extracts stimulated an increased pheromone emission rate in females, but glandular content of pheromone was not affected. Head extracts of H. virescens, a species with known PBAN activity, and synthetic PBAN stimulated an increased pheromone emission rate in T. ni. There was some specificity of the response of female T. ni to PBAN, in that several other unrelated polypeptides did not stimulate this type of response. Previously it had been determined that brain factors do not play a role in stimulating pheromone biosynthesis in T. ni. Our results indicate that there may be additional avenues by which PBAN or related neuropeptides control pheromone emission, including transport of pheromone reserves to the surface of the sex pheromone gland.

Evaluating Pheromone Emission Rate and Blend in Disrupting Sexual Communication of Codling Moth (Lepidoptera: Tortricidae)

Emission characteristics of 3 sex pheromone components, (E,E)–8, 10–dodecadien– 1–01[codlemone], 1–dodecanol, and I–tetradecanol, of codling moth, Cydia pomonella (L.), were determined from a polyethylene tube dispenser. A model predicting emission rate of codlemone as a function of accumulated degree hours and temperature was developed. The effectiveness of different blends and estimated emission rates of codlemone at dusk in disrupting sexual communication of codling moth were evaluated in field tests in apple ( Malus X domestica [Borkham]) during 1991–1992. In all field tests, virgin female–baited traps and releases of marked male moths were used. Traps were placed at 3 heights in the canopy in 9 orchards treated with 1,000 polyethylene tube dispensers per hectare and a single untreated orchard. Trap height significantly affected moth catch in both the pheromone–treated and untreated orchards. The difference in moth catches between pheromone–treated and the untreated orchard with respect to the estimated codlemone emission rate at dusk was substantial for each height, and tile slopes did not differ among heights. A significant negative regression was found for moth catch and the estimated codlemone emission rate from fibre dispensers aged in the field 0–120 d in small plots (0.1 hal. No difference in moth catch was found for plots treated with Celcon hollow fiber dispensers emitting codlemone versus a 3–component blend. Emission rate was a significant factor affecting moth catch. Problems associated with using these data to establish a minimum effective pheromone emission rate for disruption of codling moth are discussed.

Temporal and temperature-induced changes in emission rates and blend ratios of sex pheromone components in Trichoplusia ni

Moths that use pheromone components with different vapor pressures either must have active means of regulating the emitted blend or must be able to respond to a wider range of ratios of these components. Both temperature and previous depletion of pheromone reserves could challenge the ability of a female to maintain a constant pheromone blend ratio and emission rate. Therefore this study of the influence of temperature and time of night on pheromone emission rates and blend ratios was conducted.Increases in temperature from 15 to 30°C resulted in a significant increase (70%) in pheromone emission rate from forcibly extruded sex pheromone glands of female cabbage looper moths, Trichoplusia ni. Blend ratios of (Z)-7- and (Z)-9-tetradecenyl acetate (Z7- and Z9–14:Ac) relative to the major pheromone component (Z)-7-dodecenyl acetate (Z7–12:Ac) increased significantly with temperature.During all time periods in the scotophase, the percentages of the gland's contents of each pheromone component emitted during a 10 min period (percent depletion rates) were different, with (Z)-5-dodecenyl acetate (Z5–12:Ac) and Z7–12:Ac having the highest depletion rates and Z7–14:Ac and Z9–14:Ac the lowest, reflecting their different vapor pressures. For each compound the percent depletion rate increased steadily during the scotophase, suggesting that either the permeability of the gland's membrane to each pheromone component increased, or that a pheromone transport system became increasingly active. This may compensate for lower pheromone reserves at the end of the scotophase to maintain a relatively stable pheromone emission rate. Blend ratios of Z7–14:Ac and Z9–14:Ac in both pheromone gland extracts and volatile collections increased over the scotophase. This was likely caused by lower vapor pressures of the two 14-carbon acetates and thus a relative accumulation of these on or in the gland.

Influence of pheromone concentration and ambient temperature on flight of the gypsy moth, Lymantria dispar (L), in a sustained‐flight wind tunnel

Abstract. The effects of pheromone concentration and ambient temperature on male gypsy moth, Lymantria dispar (L.) (Lepidoptera), flight responses to pheromone were investigated in a wind tunnel. As the pheromone dose increased from 10 ng to 1000 ng, males flew at progressively slower airspeeds and ground speeds, and reduced their wingbeat frequencies. Furthermore, the moths steered significantly smaller course angles as the pheromone concentration increased, indicating that they were adopting a more upwind heading. The overall width of the flight tracks also decreased when males flew in more concentrated pheromone plumes. Estimation of plume dimensions using a male wing‐fanning assay showed that as pheromone dosage increased, the resultant active spaces became wider, indicating that an inverse relationship existed between the dimensions of the time‐averaged plume and the width of track reversals and that most turns were initiated within the plume. When males were flown at cool (20°C) and warm (26°C) ambient temperatures but to equivalent pheromone emission rates, they exhibited higher airspeeds and ground speeds at the higher temperature but steered larger course angles. Track widths, and length of track legs were, however, similar at the two temperatures. The mean turning frequency was nearly the same (c. 4 turns/s) across all the concentrations and temperatures tested even though the moths' thoracic temperature differed by 5°C when the ambient temperature was varied.

Sublethal Effects of Cypermethrin on Chemical Communication, Courtship, and Oviposition in the Cabbage Looper (Lepidoptera: Noctuidae)

Sublethal doses of cypermethrin had multiple deleterious effects on reproductive activities in the cabbage looper, Trichoplusia ni (Hubner). Cypermethrin-treated female moths were less likely to show calling behavior than control moths. However, no differences were observed between treated and control females in the pheromone emission rates or pheromone blend ratios from forcibly extruded glands. Thus, those treated females that did call probably emitted sufficient pheromone to attract mates. Pheromone-mediated flight was reduced in males treated with cypermethrin, which would result in a reduction in successful mate location by affected males. In observations of courtship, treatment of males with cypermethrin reduced their mating success, but identical treatment of females had no effect. Results of this research are compared with previous studies of the effects of sublethal doses of chlordimeform and methoprene on reproductive events in T. ni .

Effect of allatectomy and ventral nerve cord transection on calling, pheromone emission and pheromone production in Lymantria dispar

The physiological control mechanisms of calling, pheromone production, and pheromone release in female gypsy moths were investigated. No involvement of the corpora allata was found since mean pheromone emission rates from females allatectomized as larvae (14.1 ng/h) were not significantly different from sham-operated (16.4 ng/h), anaesthetized (13.1 ng/h), or untreated controls (13.1 ng/h). Neural input from the brain or other higher centres of the nervous system, however, appeared critical since females which received ventral nerve cord transection anterior to the terminal abdominal ganglion between 0 and 24 h after pupation showed significant reductions in both gland-extractable pheromone ( x = 8.7 ng) and pheromone emission rate ( x = 2.1 ng/h) compared with controls ( x = 25.0 ng and x = 13.1 ng/h, respectively). Differences in calling behaviour were also observed; in control females, the duration of ovipositor protraction was about 16.5 s and retraction about 1.3 s, in ventral nerve cord-transected females the ovipositor was maintained in a full or partially protruded state for periods longer than 300 s. Post-operative inspection of the terminal abdominal ganglion revealed fewer descending nerve branches in ventral nerve cord-transected females compared to controls.

Initiation and Termination of Oriental Fruit Moth Male Response to Pheromone Concentrations in the Field

The distance from the pheromone source at which Grapholitha molesta (Busck) males initiated walking, upwind flight, or wing fanning while walking varied directly with the pheromone emission rate. Roughly a 10-fold increase in emission rate resulted in a ca. 2-fold increase in mean maximum distance for initiation of these behaviors. Also, an apparent upper concentration threshold in males caused upwind flight to be terminated at increasing distances from the source with increasing emission rates. Thus, upper and lower thresholds apparently determine the boundaries of the “active distance” for upwind flight. There was much daily variation in mean maximum active distance, possibly due to temperature effects upon male threshold. The active distance estimates were used to design an optimal monitoring trap deployment strategy to minimize attraction of males from areas surrounding orchards. Using Bossert and Wilson's equation for active space, the average lower (initiation) threshold for upwind flight was 7.2 × 10−17 g/cm3 and the upper (termination) threshold was 2.1 × 10−13 g/cm3. Their model should be altered so that active space is defined as the space where pheromone concentration is within both lower and upper thresholds for a particular behavior.

Modeling the dynamics of mountain pine beetle aggregation in a lodgepole pine stand.

At least once a year the mountain pine beetle searches for lodgepole pines that provide a suitable habitat for a new brood. After attacking females feed, they produce an attractant pheromone that causes beetles to aggregate and, during outbreaks, to usually mass attack the "focus" tree. Near the completion of mass attack, incoming beetles are repelled and initiate attacks on adjacent "recipient" trees. An understanding of this "switching" process is useful for prescribing measures that minimize beetle damage.A mathematical model was developed to (1) describe beetle aggregation, (2) predict the relation of tree susceptibility and switching to changes in beetle density, (3) provide a structure for current knowledge, and (4) pose questions for further research. The model indicates that a high population density ensures mass aggregation and consequently successful tree colonization and switching. The model also indicates that the number of beetles attracted per attacking beetle differs from tree to tree, possibly depending on resin quality and production and/or the local flying density of beetles. Field and model results indicate that tree size appears to affect the repellence of beetles, suggesting that the attack density or the visual attractiveness of large trees is a factor. Further research could be directed at our assumptions on host resistance, repellence, pheromone emission rates, threshold concentrations, navigation, and pheromone dispersion.