Pheromone Baits Research Articles

Population Dynamics of Ips sexdentatus (Börner) in the Czech Republic

Recently, an outbreak of Ips sexdentatus (Börner, 1776) has caused considerable damage in the pine forests of the Czech Republic. As historical data on the biology of this pest are scarce due to its rare occurrence in recent decades, our work focused on monitoring flight activity and voltinism and investigating methods for monitoring its activity during the growing season. Observations were conducted from March to September 2021 and 2022 at three sites using 12 Theysohn traps with four types of pheromone lures (ACUMIPROTECT, ACUWIT, SEXOWIT and Pheagr IAC) together with data loggers to record weather conditions. The first beetles occurred in early May (daily mean temperatures above 13 °C). After the first egg laying stage, females re-emerged to establish a sister brood. The maximum flight activity appeared between late June and mid-July (daily mean temperatures about 20 °C), and the offspring occurred at the turn of June/July and in the first half of August. Since then, flight activity had a downward trend and quietened in September. According to the data, monitoring of I. sexdentatus should be conducted between May and September using the ACUMIPROTECT pheromone bait exhibiting the highest capturing efficacy. In future, however, the behavior of I. sexdentatus might alter due to climate change.

Spruce Protection against Ips typographus with Anti-Attractant Blend of Tree-Based Semiochemicals: From Small Experimental Plots to Stand Scales

Tree-killing bark beetles require rapid management, such as anti-attractants, to stop the enlargement of attack hot-spots. We tested two newer anti-attractant blends, both without verbenone and one with the addition of trans-4-thujanol, in traps against standard pheromone baits for inhibition of catch. Both blends provided effective catch reduction (>95%). We also tested these anti-attractant blends in tree protection experiments for two years. We had experimental plots with a center of an anti-attractant protected tree zone, with no traditional control area, but we followed tree kills in 10 m wide concentric rings to 100 m. In 2020, we had 12 plots, and 9 plots in 2021. Monitoring by low-strength pheromone traps followed beetle flight averaging 300/trap during the shorter period, August 2020, and 5000/trap during the longer period, May to August 2021. The blends of anti-attractants were 100% effective in avoiding tree mortality in both treated trees and their surroundings. There were no bark beetle attacks on any treated trees, and there was zero tree mortality up to 19 m in 2020, and up to 30 m in 2021, thus full protection to circa 20 m. The density of killed trees then increased from close to zero, over 20 to 50 m, reaching a level of ca 30 (trees/ha) then declined. The spatial pattern of tree mortality on our experimental plots was highly heterogeneous and individual 10m-ring data points on tree kill density could not be statistically separated. In contrast, a non-linear regression model showed a continuous increase of attacks over the distance from the center to a peak ca 60m, followed by a decline. This model agrees partly with the only similar study in the literature, but importantly, it does not give a peak of kill density at distances between the first and second rings close to treatment zones. Such patterns of close-quarter kills have been observed as a “switching” of attack in this and other scolytid systems manipulated by anti-attractants, but not in the present study, likely due to the elimination of verbenone from our blends.

Identification of sex-specific compounds in the invasive four-eyed fir bark beetle Polygraphus proximus

Polygraphus proximus, a four-eyed fir bark beetle, is an invasive bark beetle species which has caused extensive damage to forests of Abies sibirica in southern and western Siberia and to Abies species in the European part of Russia. There is a high risk that the pest insect will spread to areas where it is currently not considered present, such as the European Union. In these areas, it threatens to attack conifer forests of various species which may result in major environmental and economic impact. The aim of this study was to identify pheromone components of P. proximus that can be used as pheromone baits. Males and females of P. proximus were allowed to bore into the bark of stem sections of Abies sibirica at the laboratory, and volatiles were collected with solid-phase microextraction (SPME). Analyses of these extracts with gas chromatography-mass spectrometry (GC–MS) revealed several sex-specific compounds. In total, twelve male-specific compounds and one female-specific compound were identified. The major male-specific compound determined by GC peak area was (Z)‐2‐(3,3‐dimethylcyclohexylidene)‐ethanol [(Z)-DMCHE] and the minor male-specific compounds were 3-methyl-3-buten-1-ol, 3-methyl-2-buten-1-ol, 3-methyl-2-butenal, benzyl alcohol, fragranol, 7-methyl-3-methylene-6-octen-1-ol, (Z)- and (E)-2-(3,3-dimethylcyclohexylidene)-acetaldehyde, geraniol, geranial and papayanol. The only female-specific compound was identified as 1-hexanol. Two of the male-specific compounds, (Z)‐DMCHE and 3-methyl-2-buten-1-ol were shown to attract males and females of P. proximus in field studies. Thus, we now for the first time can present the structures of two male-specific components that are biologically active parts of P. proximus aggregation pheromone. However, some chemical communication overlap between P. proximus and P. subopacus needs to be further investigated as (Z)‐DMCHE also attracted males and females of P. subopacus.

Responses of Red Flour Beetle Adults, Tribolium castaneum (Coleoptera: Tenebrionidae), and Other Stored Product Beetles to Different Pheromone Trap Designs.

Simple SummaryTraps are used to monitor insect pests in stored food product habitats, and information on insects trapped can be used for making control decisions in pest control programs. A special trap is used for adults of the red flour beetle, one of the most serious pests of flourmills worldwide. The red flour beetle trap is a “pitfall” design wherein a walking beetle orients to the trap, it climbs up the inclined side of the trap to the top of a cup, it then slips or walks over the edge of the cup. The beetle falls into the bottom of the cup, where it is retained and killed inside the food oil placed in the bottom of the cup. However, dusty environments can result in the pitfall trap operating poorly and not capturing beetles at an optimum level. This research showed that a dust cover can be applied to the top of a baited pitfall trap and significantly improve capture of beetles in dusty environments of a flourmill. The dust cover was incorporated into the commercial pitfall trap product and now is known as the Dome trap, which is widely used for pest management of flour beetles and other stored product insects throughout the grain and food industries in many countries.A series of laboratory and field experiments were performed to assess the responses of Tribolium castaneum (Herbst) and other stored-product beetles to pheromone-baited traps and trap components. A commercial Tribolium pitfall trap called the Flit-Trak M2, the predecessor to the Dome trap, was superior in both laboratory and field experiments over the other floor trap designs assessed at capturing walking T. castaneum. In field experiments, Typhaea stercorea (L.) and Ahasverus advena (Stephens) both preferred a sticky trap to the pitfall trap. Although the covered trap is effective at capturing several other species of stored product beetles, the synthetic Tribolium aggregation pheromone lure is critical for the pitfall trap’s efficacy for T. castaneum. Although the food-based trapping oil used in the pitfall trap was not found to be attractive to T. castaneum when assayed alone, it had value as an enhancer of the pheromone bait when the two were used together in the trap. A dust cover modification made to go over the pitfall trap was effective in protecting the trap from dust, although the trap was still vulnerable to dust contamination from sanitation techniques that used compressed air to blow down the mill floors. Capture of T. castaneum in the modified trap performed as well as the standard trap design in a non-dusty area of a flour mill, and was significantly superior over the standard trap in a dusty area. T. castaneum responded in flight outside a flourmill preferentially to multiple funnel traps with pheromone lures compared to traps without pheromone.

Efficiency of volatile baited sticky traps for the Tarnished Plant Bug (Lygus lineolaris) in strawberry fields

AbstractInsecticides have adverse effects on human health and the environment. Thus, the development of non‐chemical replacement to manage insect pests is urgent. An alternative is to bait sticky traps with attractive insect sex pheromones or plant volatiles. In Quebec, the tarnished plant bug (Lygus lineolaris) is a major insect pest. We tested the efficiency of sex pheromones (mixture of hexyl butyrate (HB), (E)‐2‐hexenyl butyrate (E2HB) and (E)‐4‐oxo‐2‐hexenal (KA)) and sunflower (Helianthus annuus) volatiles (pinene, sabinene and phenylacetaldehyde) as sticky trap baits for the tarnished plant bug in strawberry fields of the Laurentians in Southern Québec, Canada. The pheromones decreased the number of tarnished plant bug caught in the traps compared to a control. The sunflower volatile did not have any effect on the number of individuals caught in the traps. Different Lygus species use HB, E2HB and KA in different ratios for sexual signals and alarm signals and for species recognition. GC‐MS analysis of the sex pheromone bait revealed that the ratios between the three main compounds did not match the intended ratio for the L. lineolaris species. This mismatch probably explains our results. Individuals were not attracted to sunflower volatiles. Our results point to the difficulty of manufacturing and using sex pheromones as baits. Future work should assess the effect of several pheromone ratios.

Thousand cankers disease in Juglans: Optimizing sampling and identification procedures for the vector Pityophthorus juglandis, and the causal agent Geosmithia morbida

Lindgren funnel traps were used to monitor Pityophthorus juglandis occurrence. Traps were placed directly on walnut trees, with the top tied to one of the lower branches (about 2m high). An 8-funnel model was used instead of a 4-funnel trap, with the specific pheromone bait positioned between the fourth and the fifth funnel. Traps were customized with a 5mm metal mesh which was placed inside the bottom funnel so that debris (mainly foliage) and larger non-target insects would not end up inside the collecting jar. Geosmithia morbida was isolated from beetle adults, larvae and necrotic woody tissue around beetle galleries. Contaminant-free colonies were subcultured in purity and identified by: a) colony phenotyping [morphology, texture and pigmentation; margin type (regular/irregular; lobed/non-lobed); mycelium compactness; surface bumpiness; growth/temperature relationships]; b) micromorphology: type, morphology and ontogeny of conidiophores, metulae and phialides; conidiogenesis; shape, dimension and pigmentation of conidia; c) DNA fingerprinting.•Our protocol was customized to prevent traps from swinging in the wind and to optimize beetle catches by transversely fixing the bottom of funnel traps to the tree trunk with wooden shafts for stability.•To enhance fungus isolation in purity, a semi-selective Potato Dextrose Agar (PDA) medium, enriched with the antibiotics Ampicillin (Policillin-N) and Rifampicin (Rifamycin), was devised to prevent contamination by Gram-positive and Gram-negative bacteria and by mycobacteria.

Trapping strategy for Monochamus sutor and Monochamus galloprovincialis: potential vectors of the pine wood nematode in Scandinavia

Abstract The pine wood nematode Bursaphelenchus xylophilus is a threat to pine forests in Europe. Annual detection, and delimiting surveys if detected, are mandatory in the European Union. The trapping of Monochamus beetles, vectors of pine wood nematode, is included in both types of survey. The efficient use of traps increases the probability of detecting the pine wood nematode. How stand type, bait composition, wet or dry collecting jars, and trapping period during the summer affect the catches of Monochamus was investigated in central Sweden. Monochamus sutor and Monochamus galloprovincialis occurred together in half of the trapping locations, suggesting that the two species could interact as vectors for the pine wood nematode. Baited traps caught 25‐ to 30‐fold more M. sutor than unbaited traps. Monochamus sutor was four‐ to seven‐fold more abundant on clear‐cuts than in pine stands, whereas numbers of M. galloprovincialis were similar in both habitats. There was no difference in catch between fresh and old clear‐cuts for M. sutor. The addition of α‐pinene to the pheromone baits increased catches of M. sutor by 1.6‐fold on old clear‐cuts, whereas there was no difference for M. galloprovincialis. Wet traps caught approximately two‐fold more M. sutor than dry traps. Most M. sutor were caught in June and July, whereas the flight period of M. galloprovincialis started approximately 1 month later and peaked in July. Based on the results, a trapping strategy is presented for M. sutor and M. galloprovincialis in Scandinavia.

Optimizing the attractiveness of pheromone baits used for trapping the four‐eyed spruce bark beetle Polygraphus poligraphus

AbstractBark beetles have caused extensive damage to forests in central Sweden during the past decade, and the four‐eyed spruce bark beetle, Polygraphus poligraphus, seems to be involved. However, its role in these bark beetle outbreaks is still not clear. The purpose of this study was to develop an efficient pheromone bait for P. poligraphus, which would make it possible to study the species more carefully and thereby contribute to protect exposed forests in an environmentally friendly way. Three field studies were conducted in 2015, 2016 and 2018 in Medelpad, county of Västernorrland, Sweden. The pheromone of P. poligraphus, (−)‐terpinen‐4‐ol, was tested at different release rates and in different enantiomeric purities, to find the most attractive formulation for the beetles. It was also tested in combination with racemic frontalin, a compound which has previously been shown to produce a synergistic effect together with (−)‐terpinen‐4‐ol of low enantiomeric purity; 52% ee. Other compounds, chosen based on responses from electroantennographic studies, were also tested in an attempt to find additional attractants and repellents for P. poligraphus. The most attractive treatment tested was enantiomerically pure (−)‐terpinen‐4‐ol (99% ee). When the enantiomeric purity was lower (50% ee), the trap catches was lowered to levels comparable to the catches for unbaited control traps. A strong synergistic effect with frontalin was observed for (−)‐terpinen‐4‐ol of low enantiomeric purity (50% ee) but not for the enantiomerically pure compound (99% ee). The release rate of (−)‐terpinen‐4‐ol (99% ee) was shown to be an important factor. For the combination of frontalin and (−)‐terpinen‐4‐ol (50% ee), the attraction seemed strongest when (−)‐terpinen‐4‐ol was released at a higher rate than frontalin. An interesting and novel result was that a repellent compound, α‐terpineol, was identified in our studies. Our results from field studies and electroantennography recordings also indicate that (+)‐terpinen‐4‐ol is a repellent for P. poligraphus.

Comparison of different pheromone traps for monitoring of click beetle Agriotes ustulatus (Coleoptera Elateridae)

The effectiveness of two trap types (YATLORf and VARb3 with CSALOMON® sex pheromone bait) for monitoring click beetle Agriotes ustu latus was compared near Karcag (East Hungary) in 2016. Additionally effectiveness of YATLORf traps placed on ground and placed on a 25 cm high mound was also compared. Contrary to our expectations traps caught very few individuals thus our study could provide only preliminary results. Between traps and methods there were not significant differences but YATLORf traps placed on mounds caught more individuals than others. The swarming imagos of A. ustulatus were also detected two weeks earlier in 2016 than as usual. To prove the effect of the way of usage on the effectiveness of YATLORf traps new studies should be made.

Sticky traps saturate with navel orangeworm in a nonlinear fashion

Trapping is an essential tool used to decide the need for and/or timing of an insecticide application. The assumption is that the information is accurate, but accuracy is dependent on trap reliability and efficacy. One factor that affects reliability is trap saturation, defined as the measurable decrease in trap capture due to reduced trapping effectiveness caused by the accumulation of insects already in a trap. In this study, we used unmated female navel orangeworm (NOW, Amyelois transitella (Walker)) as sex pheromone baits in wing traps that varied by color and glue/trapping surface in order to evaluate saturation thresholds and quantify trap effectiveness. Effectiveness decreased in each type of sticky trap as the number of insects caught increased, because of the accumulation of scales and insect bodies on the glue surface. The continued accumulation of insects further reduced trap capture, and this decrease in capture could be described by a regression using a power transformation. The resulting saturation equations that we calculated will help pest control advisers and growers interpret their trap data by better estimating the relationship between the number of males trapped versus those that visited the trap.

Sustainable Control of Oriental Fruit Moth, Cydia molesta Busck, Using Isomate OFM Rosso Dispensers in Peach Orchards in Bulgaria

The trials were carried out in the years 2011-2013 in an isolated peach experimental orchard of one ha in the Fruit Growing Institute, Plovdiv – Central South Bulgaria. Mating disruption (MD) was tested as an alternative method controlling oriental fruit moth (OFM), Cydia molesta Busck from post-bloom till harvest. Isomate® OFM rosso (Shin Etsu - Japan) pheromone dispensers were installed once during the season, before the start of OFM flights. In 2013 Cidetrak® PTB dispensers were used against Anarsia lineatella Zell. For monitoring of the pests one type of pheromone traps was used in this experiment - PHEROCON® VI Delta traps (Trece, USA) with a sticky changeable bottoms. The pheromone baits are a products of Trece, Inc. USA. In the reference, conventionally treated orchard, 5-9 insecticide treatments were applied to control oriental fruit moth, peach twig borer (PTB), aphids and other pests. In spite of that, the fruit damage ranges from 3.6 to 5.2 % in the successive years. Percentage of damage in the experimental orchard treated with Isomate® OFM rosso was 0.1 and 0.3 %, i.e. rather below the economical threshold; no outbreak of the OFM appearance was noted. So, the MD method, with use of the Isomate® OFM rosso dispensers, proved to be an effective means of control even in a small size orchard lots. The results obtained may open the possibilities of practical use of the method of mating disruption in Bulgaria. This method should favour preservation of the natural environment and enable production of healthy fruits, not polluted by chemicals.

Bed bug aggregation pheromone finally identified.

Bed bugs have become a global epidemic and current detection tools are poorly suited for routine surveillance. Despite intense research on bed bug aggregation behavior and the aggregation pheromone, which could be used as a chemical lure, the complete composition of this pheromone has thus far proven elusive. Here, we report that the bed bug aggregation pheromone comprises five volatile components (dimethyl disulfide, dimethyl trisulfide, (E)-2-hexenal, (E)-2-octenal, 2-hexanone), which attract bed bugs to safe shelters, and one less-volatile component (histamine), which causes their arrestment upon contact. In infested premises, a blend of all six components is highly effective at luring bed bugs into traps. The trapping of juvenile and adult bed bugs, with or without recent blood meals, provides strong evidence that this unique pheromone bait could become an effective and inexpensive tool for bed bug detection and potentially their control.

Bed Bug Aggregation Pheromone Finally Identified

AbstractBed bugs have become a global epidemic and current detection tools are poorly suited for routine surveillance. Despite intense research on bed bug aggregation behavior and the aggregation pheromone, which could be used as a chemical lure, the complete composition of this pheromone has thus far proven elusive. Here, we report that the bed bug aggregation pheromone comprises five volatile components (dimethyl disulfide, dimethyl trisulfide, (E)‐2‐hexenal, (E)‐2‐octenal, 2‐hexanone), which attract bed bugs to safe shelters, and one less‐volatile component (histamine), which causes their arrestment upon contact. In infested premises, a blend of all six components is highly effective at luring bed bugs into traps. The trapping of juvenile and adult bed bugs, with or without recent blood meals, provides strong evidence that this unique pheromone bait could become an effective and inexpensive tool for bed bug detection and potentially their control.

Monitoring and Mass Trapping of the Codling Moth, Cydia pomonella, by the Use of Pheromone Baited Traps in Kargil, Ladakh, India

This study was conducted in six major apple growing areas of the Kargil region during 2009 and 2010; pheromone traps were evaluated for the monitoring and mass trapping of the codling moth. Monitoring the population dynamics of Cydia pomonella in 2009 revealed that the first catch was observed on 21 May, the highest on 11 June, and the lowest on 13 August at all of the locations. The dynamics were similar, but the population was lower in 2010. Climatic variables were more or less similar in both of the years. So, effective monitoring for the codling moth is essential and was highest in Hardas and lowest in Gongma during 2009 and highest in Shilikchey and lowest in Poyen in 2010.

High-accuracy sampling of saproxylic diversity indicators at regional scales with pheromones: The case of Elater ferrugineus (Coleoptera, Elateridae)

The rare beetle Elater ferrugineus was sampled at 47 sites in the county of Östergötland, Sweden by means of pheromone-baited traps to assess its value as an indicator species for hollow oak stands rich in rare saproxylic beetle species. In addition, Osmoderma eremita was also sampled with pheromone baits. These data were then compared against species survey data collected at the same sites by pitfall and window traps. Both species co-occur with many Red Listed saproxylic beetles, with E. ferrugineus being a somewhat better indicator for the rarest species. The conservation value of a site (measured as Red List points or number of Red Listed species) increased with the number of specimens of E. ferrugineus and O. eremita caught. Accuracy of sampling by means of pheromone trapping turned out to be radically different for the two model species. E. ferrugineus traps put out during July obtained full accuracy after only 6days, whereas O. eremita traps needed to be out from early July to mid-August in order to obtain full accuracy with one trap per site. By using E. ferrugineus, or preferably both species, as indicator species, accuracy would increase and costs decrease for saproxylic biodiversity sampling, monitoring and identification of hotspots.

Preliminary Research on the use of Pheromones on European Cherry Fruit Fly (Rhagoletis Cerasi L.)

The European cherry fruit fly, Rhagoletis cerasi (L.) (Diptera: Tephritidae), is one of the most destructive pest in cherry and sweet cherry orchards. Because of the low tolerance for damaged fruit on the market and the restrictions from E.U regarding insecticides, new envioramental safe methods begin to be developed. This paper prezents preliminary research in monitoring and control of Rhagoletis cerasi L. with 5 diffent formulations of specific pheromon (pheromon prodeced by ICC Raluca Ripan Cluj-Napoca) 4 of them, have not been tested yet. Adult flight was monitored twice a week on 22 yellow colored traps, 17 with certified pheromone and 27 with the 4 new synthesized formulations. Traps were placed in two orchards: one in which chemical treatments have been performed and another plantation where no chemical treatments were applied. In the orchard where they applied chemical treatments, the average catch on colored traps was 28.31 adults/trap and in baited pheromone traps the average fluctuated between 11 adults/ trap in V3 and 28,6 adults per trap in V2. In the untreated orchard, the average number of catches on colored panels was 23.33 and in the variants with pheromone baits, this parameter was between 8.5 adults/trap in V5 and 44 adults/trap in V2.Rhagoletis cerasi level of population differ from a plantation to another and that is not strictly related to applied technology culture. Yellow panels shows good functionality in capturing adults. Between the pheromone baited traps that are in the first stage of testing, higher number of captures than yellow panel variants, showed the variant V2.

Short-term but not long-term patch avoidance in an orchid-pollinating solitary wasp

The success of exploitative attraction of insect pollinators to rewardless flowers may depend on a constrained capacity for learning. In the case of sexually deceptive orchids, the extent to which pollinators can avoid dishonest signals through learning or adaptation is poorly known. We used field experiments with synthetic pheromone baits in concert with novel miniaturized marking techniques to investigate patterns of behavior and movement in Neozeleboria cryptoides , the wasp pollinator of the sexually deceptive orchid Chiloglottis trapeziformis . In trials of 4- and 60-min duration, visitation rates to synthetic sex pheromone declined rapidly after the first minute and remained low, suggesting short-term avoidance. Using spatially explicit capture–recapture models, we then assessed if wasps maintained this avoidance for more than 24h. Among our 4 competing behavioral models, the best supported model was one which showed an increase in detection probability at a location for wasps that had previously been caught at that location. Therefore, we found no evidence for long-term patch avoidance. If spatial learning underpins the short-term avoidance we observed, then this information appears not to be retained beyond 24h. The typical patterns of N. cryptoides movement (range = 0–161 m, median = 14.8) coupled with short-term patch avoidance likely promote outcrossing in the clonal, self-compatible orchid it pollinates.

Armadilhas de feromona sexual com luz para captura em masse de Tuta Absoluta (Meyrick), sim ou não?

In an assay performed in November 2010, adults captured in sexual pheromone water traps with and without light were counted. In traps with light a part of the insects were sampled for sex identification. Water traps for mass trapping which combined the attractive effect of sexual pheromone and light captured higher levels of Tuta absoluta adults than the traditional ones, with pheromone bait only. However, these traps were unable to capture females of T. absoluta (about 1.1% of the captured adults were females), an expected event due to the light effect. Although capturing higher number of males of T. absoluta, the lack of female captures makes it hard to justify the use of these traps,

Seasonal monitoring of the latticed heath,Chiasmia clathrata(Linnaeus, 1758) (Lepidoptera: Geometridae) by pheromone traps in two regions of Bulgaria

Monitoring the seasonal flights of the Latticed heath, Chiasmia clathrata (Lepidoptera: Geometridae), was carried out using home made sticky delta traps baited with pheromone caps purchased from CSALOMON® (Plant Protection Institute, Hungary, Budapest). The monitoring was conducted in alfalfa fields in Pazardzhik and Sofia regions in Bulgaria during 2007–2009. The flight of C. clathrata at the investigated sites started at the very beginning of April and lasted until the middle-end of September. Three relatively well-defined peaks, indicating three generations, were recorded in Sofia region. Thus, the flight period and the flight of the separate generations of the pest were defined more accurately than it has been reported earlier. Pheromone baits, products of CSALOMON ® are potent and species specific tools for detecting the presence and seasonal monitoring of C. clathrata.

Intended and unintended receivers of the male pheromones of the burying beetles Nicrophorus humator and Nicrophorus vespilloides

Male Nicrophorus beetles (Coleoptera: Silphidae) attract females through volatiles that are emitted at species-specific times of day. Not only beetles of the opposite sex but also conspecific males are attracted. Another observation is the co-attraction of congeners, a phenomenon that was shown in particular for Nicrophorus vespilloides Herbst, the smallest Nicrophorus species in Central Europe. In the current study, we identified the Nicrophorus humator Gleditsch male pheromone as methyl 4-methyloctanoate through gas chromatography/mass spectrometry analysis. In field experiments, we tested and compared the attractiveness of synthetic analogs of the male pheromones of N. humator and N. vespilloides in baited pitfall traps. An asymmetric cross-attraction to the synthetic male pheromones was observed, which is best explained by the skewed competitive relationship of the two species, with regard to the restricted availability of breeding resources. Nicrophorus humator is attracted by both its own male pheromone and by the pheromone of the smaller N. vespilloides, whereas N. vespilloides is almost exclusively attracted by its own male pheromone. The observed attraction of conspecific males of either species to male pheromone baits can be explained by both competition for females and competition for breeding resources.