Trail Pheromone Disruption of Argentine Ant Trail Formation and Foraging

Trail pheromone disruption of invasive ants is a novel tactic that builds on the development of pheromone-based pest management in other insects. Argentine ant trail pheromone, (Z)-9-hexadecenal, was formulated as a micro-encapsulated sprayable particle and applied against Argentine ant populations in 400 m² field plots in Hawai‘i Volcanoes National Park. A widely dispersed point source strategy for trail pheromone disruption was used. Traffic rates of ants in bioassays of treated filter paper, protected from rainfall and sunlight, indicated the presence of behaviorally significant quantities of pheromone being released from the formulation for up to 59 days. The proportion of plots, under trade wind conditions (2–3 m s⁻¹), with visible trails was reduced for up to 14 days following treatment, and the number of foraging ants at randomly placed tuna-bait cards was similarly reduced. The success of these trail pheromone disruption trials in a natural ecosystem highlights the potential of this method for control of invasive ant species in this and other environments.     

Argentine Ant Trail Pheromone Disruption is Mediated by Trail Concentration

Argentine ant trail pheromone disruption, using continuous release of the trail pheromone compound (Z)-9-hexadecanal, reduces the incidence of trails and foraging rates of field populations. However, little is known about the concentrations of pheromone required for successful disruption. We hypothesized that higher pheromone quantities would be necessary to disrupt larger ant populations. To test this, we laid a 30-cm long base trail of (Z)-9-hexadecanal on a glass surface at low and high rates (1 and 100 pg/cm) (Trail 1), and laid a second, shorter trail (Trail 2, 10 cm long, located 1.5 cm upwind) near the middle of Trail 1 at six rates (1, 10, 100, 1,000, 10,000, and 100,000 pg/cm). We then recorded and digitized movements of individual ants following Trail 1, and derived a regression statistic, r ², as an index of trail integrity, and also recorded arrival success at the other end of the trail (30 cm) near a food supply. Disruption of trails required 100 fold more pheromone upwind, independent of base-trail concentration. This implies that in the field, trail disruption is likely to be less successful against high ant-trail densities (greater concentration of trail pheromone), and more successful against newly formed or weak trails, as could be expected along invasion fronts.     

Trail Pheromone Disruption of Red Imported Fire Ant

The fire ant, Solenopsis invicta (Hymenoptera: Formicidae), is considered one of the most aggressive and invasive species in the world. Toxic bait systems are used widely for control, but they also affect non-target ant species and cannot be used in sensitive ecosystems such as organic farms and national parks. The fire ant uses recruitment pheromones to organize the retrieval of large food resources back to the colony, with Z,E-α-farnesene responsible for the orientation of workers along trails. We prepared Z,E-α-farnesene, (91% purity) from extracted E,E-α-farnesene and demonstrated disruption of worker trail orientation after presentation of an oversupply of this compound from filter paper point sources (30 μg). Trails were established between queen-right colony cells and food sources in plastic tubs. Trail-following behavior was recorded by overhead webcam, and ants were digitized before and after presentation of the treatment, using two software approaches. The linear regression statistic, r ² was calculated. Ants initially showed high linear trail integrity (r ² = 0.75). Within seconds of presentation of the Z,E-α-farnesene treatment, the trailing ants showed little or no further evidence of trail following behavior in the vicinity of the pheromone source. These results show that trailing fire ants become disorientated in the presence of large amounts of Z,E-α-farnesene. Disrupting fire ant recruitment to resources may have a negative effect on colony size or other effects yet to be determined. This phenomenon was demonstrated recently for the Argentine ant, where trails were disrupted for two weeks by using their formulated trail pheromone, Z-9-hexadecenal. Further research is needed to establish the long term effects and control potential for trail disruption in S. invicta.     

Mellein, a Trail Pheromone Component of the Ant Lasius fuliginosus

3,4-Dihydro-8-hydroxy-3-methylisocoumarin (mellein) and 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one are among the volatile constituents identified from the hindgut of the formicine ant Lasius (Dendrolasius) fuliginosus Mellein induces trail-following behavior in worker ants of this species and evokes electrophysiological responses from their antennae. The trail-following activity released by (R)-(–)-mellein is significantly higher than that elicited by its (S)-(+) antipode, or the racemic mixture. The above-mentioned pyranone is found also in the honeydew of aphids, the customary diet of this ant species. The pyranone also evokes some trail-following behavior, but its activity is far less pronounced than that of mellein. Apparently, extra pheromone components are present in the hindgut, since the activity of these two constituents, either individually or as a mixture, does not completely account for the total activity released by a hindgut extract containing similar amounts of these two compounds.     

Hexyl Decanoate, the First Trail Pheromone Compound Identified in a Stingless Bee, Trigona recursa

Foragers of many species of stingless bees guide their nestmates to food sources by means of scent trails deposited on solid substrates between the food and the nest. The corresponding trail pheromones are generally believed to be produced in the mandibular glands, although definitive experimental proof has never been provided. We tested the trail following behavior of recruits of Trigona recursa in field experiments with artificial scent trails branching off from natural scent trails of this stingless bee. First-time recruits (newcomers) did not follow these trails when they were laid with pure solvent or mandibular gland extract. However, they did follow trails made with labial gland extract. Chemical analyses of labial gland secretions revealed that hexyl decanoate was the dominant component (72.4 ± 1.9% of all volatiles). Newcomers were significantly attracted to artificial trails made with synthetic hexyl decanoate, demonstrating its key function in eliciting scent-following behavior. According to our experiments with T. recursa, the trail pheromone is produced in the labial glands and not in the mandibular glands. Hexyl decanoate is the first component of a trail pheromone identified and proved to be behaviorally active in stingless bees.     

Sex Pheromone of Queens of the Slave-Making Ant, Polyergus breviceps

The sex attractant pheromone produced in mandibular glands of queens of the slave-making ant Polyergus breviceps has been identified as a blend of methyl 6-methylsalicylate and 3-ethyl-4-methylpentanol. In field trials, each compound alone was completely unattractive to males, whereas blends of the two compounds attracted hundreds of males within a couple of hours.     

Diet-Related Modification of Cuticular Hydrocarbon Profiles of the Argentine Ant, <Emphasis Type="Italic">Linepithema humile</Emphasis>, Diminishes Intercolony Aggression

Territorial boundaries between conspecific social insect colonies are maintained through a highly developed nestmate recognition system modulated by heritable and, in some instances, nonheritable cues. Argentine ants, Linepithema humile, use both genetic and environmentally derived cues to discriminate nestmates from nonnestmates. We explored the possibility that intraspecific aggression in the Argentine ant might diminish when colonies shared a common diet. After segregating recently field-collected colony pairs into high or moderate aggression categories, we examined the effect of one of three diets: two hydrocarbon-rich insect prey, Blattella germanica and Supella longipalpa, and an artificial (insect-free) diet, on the magnitude of aggression loss. Aggression diminished between colony pairs that were initially moderately aggressive. However, initially highly aggressive colony pairs maintained high levels of injurious aggression throughout the study, independent of diet type. Each diet altered the cuticular hydrocarbon profile by contributing unique, diet-specific cues. We suggest that acquisition of common exogenous nestmate recognition cues from shared food sources may diminish aggression and promote fusion in neighboring colonies of the Argentine ant.     

Trail pheromone of leaf-cutting antAcromyrmex subterraneus subterraneus (Forel)

The trail pheromone ofAcromyrmex subterraneus subterraneus consists simply of the heterocyclic ester methyl 4-methylpyrrole-2-carboxylate in the venom reservoir of workers at about 1.2 ng/ant. No pyrazines were detected, and no enhancement of trail-following was observed when pyrazines were added to the pyrrole compound.     

Simultaneous Disruption of Pheromone Communication in Choristoneura rosaceana and Pandemis limitata with Pheromone and Antagonist Blends

In British Columbia, trapping and wind-tunnel studies demonstrated that (Z)-9-tetradecenyl acetate (Z9–14:OAc), a minor component of the sex pheromone for Pandemis limitata, acted as a pheromone antagonist to a sympatric species, Choristoneura rosaceana. Addition of >1% Z9–14:OAc to the four-component C. rosaceana pheromone in a wind tunnel resulted in significant reductions in the proportion of male C. rosaceana that wing fanned, locked on to the plume in flight, oriented upwind, and made source contact, compared to the responses to the pheromone alone. Disruption of pheromone communication was tested in 33.3 × 33.3-m plots, at a release rate of 10 mg/ha/hr using Conrel fiber dispensers. Z9–14:OAc applied alone did not disrupt orientation to virgin-female-baited traps for either C. rosaceana or P. limitata. A 1:1 mixture of Z9–14:OAc and the four-component C. rosaceana pheromone was as effective as the pheromone alone at disrupting orientation of C. rosaceana males to virgin-female-baited traps, demonstrating that disruption apparently did not occur through false-trail following. The 1:1 mixture of Z9–14:OAc and the C. rosaceana pheromone also reduced catches of P. limitata males in virgin-female-baited traps, but not significantly more than the 83% disruption caused by the pheromone alone. Therefore, the C. rosaceana pheromone could be used alone or with Z9–14:OAc to disrupt communication and, presumably, mating in both leafrollers simultaneously.     

Factors Influencing Responses to Alarm Pheromone by Larvae of Invasive Cane Toads, <Emphasis Type="Italic">Bufo marinus</Emphasis>

If pheromonal communication systems of invasive species differ from those of native biota, it may be possible to control the invader by exploiting that difference. When injured, the larvae of cane toads, Bufo marinus, an invasive species of major concern in tropical Australia, produce species-specific chemical cues that alert conspecific tadpoles to danger. Repeated exposure to the alarm chemical reduces tadpole survival rates and body sizes at metamorphosis and, thus, could help control toad populations. To evaluate the feasibility of this approach, we need to know how the intensity of toad tadpole response to the alarm chemical is affected by factors such as water temperature, time of day, larval stage and feeding history, geographic origin of the tadpoles, and habituation. Information on these topics may enable us to optimize deployment, so that tadpoles encounter pheromone at the times and places that confer maximum effect. In our studies, tadpole density, nutritional state, larval stage, and geographic origin had little effect on the intensity of the alarm response, but tadpoles reacted most strongly in higher water temperatures and during daylight hours. Repeated, once-daily exposure to pheromone did not induce habituation, but repeated exposure at 15-min intervals did not elicit further responses after 2 h total exposure. The insensitivity of response to most factors tested means that the effectiveness of the pheromone as a control agent should be relatively robust.     

Queen Sex Pheromone of the Slave-making Ant, Polyergus breviceps

Workers of the slave-making ant, Polyergus breviceps, raid nests of Formica ants and return with Formica pupae that mature into worker ants in the slave-makers’ colony. These Formica workers then tend the Polyergus brood, workers, and reproductives. During raids in the mating season, winged virgin Polyergus queens accompany the workers in the raiding columns. During the raid, the virgin queens release a pheromone that attracts males that quickly mate with the queens. We report the identification, synthesis, and bioassay of the sex attractant pheromone of the queens as an approximately 1:6 ratio of (R)-3-ethyl-4-methylpentan-1-ol and methyl 6-methylsalicylate. The ants produce exclusively the (R)-enantiomer of the alcohol, and the (S)-enantiomer has no biological activity, neither inhibiting nor increasing attraction to blends of methyl 6-methylsalicylate with the (R)-enantiomer.     

Differentiation of Competitive vs. Non-competitive Mechanisms Mediating Disruption of Moth Sexual Communication by Point Sources of Sex Pheromone (Part I): Theory1

This study establishes a theoretical framework for differentiating among possible behavioral mechanisms whereby sexual communication of moths is disrupted in crops treated with point sources of pheromone. The major mechanisms recognized in the mating disruption literature fall into two main categories: competitive (competitive attraction = false-plume-following) and non-competitive (camouflage, desensitization, and sensory imbalance). Each disruption mechanism has been precisely defined verbally, and then the distinguishing characteristics of the two categories were defined mathematically. The sets of predictions associated with each category were visualized by graphical plots of mathematical simulations. Profiles of simulated male visitation rates to pheromone-baited traps deployed in pheromone-treated crops were graphed against density of pheromone dispensers by using various types of axes. Key traits of non-competitive attraction are as follows: concave profiles on untransformed axes, with an asymptotic approach to zero catch of male moths in traps; a straight line with positive slope when 1/catch is plotted against dispenser density (Miller-Gut plot); and a straight line with negative slope when catch is plotted against dispenser density * catch (Miller-de Lame plot). Key traits of non-competitive disruption profiles include: an initial linear disruption profile on untransformed axes; a concave Miller-Gut plot; and a recurving Miller-de Lame plot. These differences in profiles provide a basis for distinguishing competitive from non-competitive mechanisms when analyzing disruption profiles from field experiments. Slopes and intercepts of these secondary plots can also reveal both male and female moth densities, if the relative attractiveness of traps, females, and dispensers is known. The absolute value of the slope of the Miller-de Lame plot is a measure of each dispenser’s activity (D _a) for suppressing catch of male moths in traps. An application activity (D _Āa) for a given dispenser can be calculated by multiplying D _a by the number of such dispensers applied per hectare of crop. ¹As this study progressed, striking similarities were noted between the kinetics of mating disruption by competitive attraction and enzyme kinetics. Because of space limitations, this congruence will be addressed in a future report.     

Variables Affecting Pheromone Concentration in Vineyards Treated for Mating Disruption of Grape Vine Moth Lobesia botrana

Airborne pheromone concentration in a field is one of the most important variables for the successful application of mating disruption in pest control. In the present paper, we estimated the pheromone concentration with field EAG recordings in vineyards and investigated parameters affecting concentration. Pheromone concentration showed a positive correlation with number of dispensers per hectare (= number of point sources). A twofold increase in the absolute number of dispensers per hectare with a constant number of point sources (two dispensers at the same location) did not significantly affect relative pheromone concentration. Measurements carried out in plots where dispensers had been applied at different heights showed highest relative pheromone concentrations in plots with dispensers at 0.1 m and 1.4 m above the ground. Those concentrations were not significantly different from each other, but were significantly higher than in plots where dispensers had been placed at a height of 2 m. Foliage of grape vines substantially affected the development of high pheromone concentrations. In summer, in vineyards with fully developed leaf canopy, significantly higher pheromone concentrations could be measured shortly after application of the dispensers compared to vineyards in spring with sparse vegetation. The decline of pheromone concentrations after removal of dispensers is significantly prolonged in full vegetation, showing the impact of plant canopy on pheromone concentrations. In contrast, ground cover between the grapevine rows did not significantly affect mean pheromone concentrations.     

Trail pheromone of the antTetramorium impurum and model compounds: Structure-activity comparisons

The major component of the trail pheromone ofT. impurum is methyl 2-hydroxy-6-methylbenzoate (methyl 6-methyl salicylate). The poison reservoir of each worker contains about 1.0 ng of this substance in the venom. To ascertain the degree of specificity of the substance as pheromone and to determine any correlation between structure and biological activity, 38 synthetic analogs were tested in a bioassay. Sixteen compounds showed activity at 100 ng per artificial trail. The importance of the methyl group and methyl ester were demonstrated, while the hydroxyl group has a relatively small effect.In part presented at the Fourth Annual Meeting of the International Society of Chemical Ecology, July 13–17, 1987, Hull, England.     

Mechanisms of Pheromone Communication Disruption in Choristoneura rosaceana Exposed to Microencapsulated (Z)-11-tetradecenyl Acetate Formulated with and Without Horticultural Oil

Flight tunnel and electrophysiological assays with male Choristoneura rosaceana Harris (Lepidoptera: Tortricidae) were conducted to investigate the non-competitive mechanisms of communication disruption caused by microencapsulated (MEC) (Z)-11-tetradecenyl acetate (3M MEC-LR) formulated with and without horticultural oil (Purespray Green). Male C. rosaceana were exposed for 1 h by resting on metal surfaces sprayed with either water, 2% oil in water, MEC-LR in water, or MEC-LR + 2% oil in water. In one experiment, sprayed surfaces were allowed to age up to 47 days in a laboratory fume hood prior to moth exposure to examine the effect of ageing on the disruptive efficacy of the formulations. In flight tunnel assays with calling females, males exposed to MEC or MEC + oil treatments for 1 h were significantly disrupted up to 1 h after exposure, and both treatments were effective for 47 days. Electroantennograms revealed no reduction in antennal sensitivity when measured 75 s after a 1-h exposure. Collectively, these results support habituation as a key mechanism of communication disruption for C. rosaceana exposed to the MEC formulations tested here. Male proximity to the pheromone-treated surfaces appears to be important in maintaining a disruptive effect as MEC treatments age and pheromone release rates decline. The addition of 2% oil increased the number of microcapsules deposited on sprayed surfaces and caused a moderate but significant increase in the disruptive effect of the MEC formulation. A better understanding of the mechanisms that underlie disruption by MEC formulations, and how an adjuvant like horticultural oil may enhance these mechanisms, may lead to improvements in this technology.     

Disruption of Membrane Integrity as a Molecular Initiating Event Determines the Toxicity of Polyhexamethylene Guanidine Phosphate Depending on the Routes of Exposure

Polyhexamethylene guanidine phosphate (PHMG-P), a cationic biocide, is widely used in household products due to its strong bactericidal activity and low toxicity. However, it causes fatal lung damage when inhaled. In this study, we investigated why PHMG-P causes fatal lung injury when inhaled, and demonstrated that the disruption of membrane integrity through ionic interaction—a molecular initiating event of PHMG-P—determines toxicity. Mice were injected intravenously with 0.9 or 7.2 mg/kg PHMG-P (IV group), or instilled intratracheally with 0.9 mg/kg PHMG-P (ITI group); they were euthanatized at 4 h and on days 1 and 7 after treatment. Increased total BAL cell count and proinflammatory cytokine production, along with fibrotic changes in the lungs, were detected in the ITI group only. Levels of hepatic enzymes and hepatic serum amyloid A mRNA expression were markedly upregulated in the 7.2 mg/kg IV and ITI groups at 4 h or day 1 after treatment, but returned to baseline. No pathological findings were detected in the heart, liver, or kidneys. To simulate the IV injection, A549, THP-1, and HepG2 cells were treated with PHMG-P in cell culture media supplemented with different serum concentrations. Increased serum concentration was associated with an increase in cell viability. These results support the idea that direct contact between PHMG-P and cell membranes is necessary for PHMG-induced toxicity.     

Disruption of foraging by argentine ants,Iridomyrmex humilis (mayr) (hymenoptera: Formicidae), in citrus trees through the use of semiochemicals and related chemicals

Foraging in trees by the Argentine ant,Iridomyrmex humilis (Mayr), was disrupted by a variety of synthetic chemicals, with the most effective chemical being farnesol. Testing of substrates for presentation of the disruptant chemicals gave some success with rubber or Tygon tubing, although best results were obtained through incorporation of the material into Stikem, which was then banded around tree trunks. Amounts of farnesol used for effective, long residual ant control were between 0.8 and 2 g per tree.     

Pesticides and Their Impairing Effects on Epithelial Barrier Integrity,Dysbiosis, Disruption of the AhR Signaling Pathway and Development of Immune-Mediated Inflammatory Diseases

The environmental and occupational risk we confront from agricultural chemicals increases as their presence in natural habitats rises to hazardous levels, building a major part of the exposome. This is of particular concern in low- and middle-income countries, such as Brazil, known as a leading producer of agricultural commodities and consumer of pesticides. As long as public policies continue to encourage the indiscriminate use of pesticides and governments continue to support this strategy instead of endorsing sustainable agricultural alternatives, the environmental burden that damages epithelial barriers will continue to grow. Chronic exposure to environmental contaminants in early life can affect crucial barrier tissue, such as skin epithelium, airways, and intestine, causing increased permeability, leaking, dysbiosis, and inflammation, with serious implications for metabolism and homeostasis. This vicious cycle of exposure to environmental factors and the consequent damage to the epithelial barrier has been associated with an increase in immune-mediated chronic inflammatory diseases. Understanding how the harmful effects of pesticides on the epithelial barrier impact cellular interactions mediated by endogenous sensors that coordinate a successful immune system represents a crucial challenge. In line with the epithelial barrier hypothesis, this narrative review reports the available evidence on the effects of pesticides on epithelial barrier integrity, dysbiosis, AhR signaling, and the consequent development of immune-mediated inflammatory diseases.     

Trail pheromone of the leaf-cutting ant,Acromyrmex octospinosus (Reich), (Formicidae: Myrmicinae)

The most active component of the trail pheromone of the leafcutting ant,Acromyrmex octospinosus, is methyl 4-methylpyrrole-2-carboxylate (I). Two pyrazine isomers (II) and (III) are present but inactive.     

Disruption of Cytosolic Folate Integrity Aggravates Resistance to Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitors and Modulates Metastatic Properties in Non-Small-Cell Lung Cancer Cells

Patients with advanced-stage non-small-cell lung cancer (NSCLC) are susceptible to malnutrition and develop folate deficiency (FD). We previously found that folate deprivation induces drug resistance in hepatocellular carcinoma; here, we assessed whether disrupted cytoplasmic folate metabolism could mimic FD-induced metastasis and affect the sensitivity of NSCLC cells to epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs). We examined whether cytosolic folate metabolism in NSCLC cells was disrupted by FD or the folate metabolism blocker pemetrexed for 1–4 weeks. Our results revealed an increase in NF-κB overexpression–mediated epithelial-mesenchymal transition biomarkers: N-cadherin, vimentin, matrix metalloproteinases (MMPs), SOX9, and SLUG. This finding suggests that the disruption of folate metabolism can drastically enhance the metastatic properties of NSCLC cells. Cytosolic FD also affected EGFR-TKI cytotoxicity toward NSCLC cells. Because SLUG and N-cadherin are resistance effectors against gefitinib, the effects of SLUG knockdown in folate antagonist–treated CL1-0 cells were evaluated. SLUG knockdown prevented SLUG/NF-κB/SOX9-mediated invasiveness and erlotinib resistance acquisition and significantly reduced pemetrexed-induced gelatinase activity and MMP gene expression. To summarize, our data reveal two unprecedented adverse effects of folate metabolism disruption in NSCLC cells. Thus, the folic acid status of patients with NSCLC under treatment can considerably influence their prognosis.