Abstract
Background and goals Pseudococcus maritimus is the primary vector of grapevine leafroll-associated viruses (GLRaVs) in Washington State vineyards and can infest grape clusters. Neonicotinoids are used widely against Ps. maritimus, but resistance potential highlights the need for integrated pest management (IPM). Additional IPM strategies are needed to improve Ps. maritimus control, slow insecticide resistance, and mitigate GLRaV spread.
Methods and key findings From 2021 to 2023, we deployed Pacific Biocontrol twist-tie pheromone dispensers on grapevines at 0, 25, 74, 148, and 247 dispensers per ha, and Trécé CIDETRAK GMB MESO dispensers at 0, 79, and 124 dispensers per ha. Male mealybug densities were monitored with Trécé Ps. maritimus lures in traps from May to October 2021 and from April to October 2022 and 2023. In all 3 yr, Ps. maritimus had two distinct flight periods but the timing and abundance of captured male mealybugs varied. Pheromone dispensers reduced peak trap captures, but no clear relationship was found between dispenser rate and Ps. maritimus capture.
Conclusions and significance This study demonstrates that mating disruption has potential applications in an IPM program for Ps. maritimus. The timing of the two annual male flights indicates a single application of a passive dispenser lasting 4 to 5 mo, or a shorter-lived sprayable formulation could cover the seasonal period. A late-April pheromone dispenser deployment is recommended for Washington State. However, monitoring is encouraged to verify application timing on an interannual basis. The dispenser deployment rate requires further assessment as there was no significant difference (p > 0.05) between the lower and higher deployment rates for male Ps. maritimus captures in sentinel traps.
Introduction
The grape mealybug, Pseudococcus maritimus (Ehrhorn), is considered to be native to North America and historically is an important insect pest of vineyards across this region (Daane et al. 2012). In Washington State, Ps. maritimus is the only mealybug species present in vineyards (Bahder et al. 2013), and is the primary vector of grapevine leafroll-associated viruses (GLRaVs) expressed as grapevine leafroll disease (GLD) (Almeida et al. 2013, Naidu et al. 2014, O’Hearn and Walsh 2021). Grapegrowers attempt to reduce the mealybug population to slow the spread of GLD and mitigate the direct impacts of mealybug feeding (Ricketts et al. 2015, Jones and Nita 2016, Bell et al. 2018, 2021, O’Hearn and Walsh 2020). Applying insecticides has been the primary strategy for managing Ps. maritimus; however, insecticide effectiveness is hampered in part by the cryptic nature and clumped distribution of Ps. maritimus within vineyards (Geiger and Daane 2001, Bahder et al. 2013).
Neonicotinoids are widely used against Ps. maritimus, but potential resistance (Bass et al. 2015) and the continued spread of GLRaVs despite toxic doses of insecticide (O’Hearn and Walsh 2020) emphasize the need for integrated pest management (IPM). While other insecticides such as spirotetramat, flupyradifurone, and buprofezin are used (Lopez et al. 2024), there is a need for a more sustainable management option to control Ps. maritimus. Hence, more species-specific, effective, and environmentally safe IPM tools should be developed to control Ps. maritimus (Daane et al. 2018, Cocco et al. 2021). Pheromone-based mating disruption is an IPM strategy that has been used in vineyards to suppress vine mealybug Planococcus ficus in California (Daane et al. 2020, Hogg et al. 2021), Israel (Sharon et al. 2016), and Europe (Cocco et al. 2018, Lucchi et al. 2019). Mating disruption typically involves using artificially synthesized pheromones at a concentration great enough in the target area to interfere with males locating and mating with adult females (Miller and Gut 2015). The sex pheromone produced by female Ps. maritimus to attract the winged adult male was identified and initially synthesized as trans-α-necrodyl isobutyrate, with a more concise synthesis published by Zou et al. (2010). Traps baited with synthetic sex pheromones have been used to monitor male Ps. maritimus populations in Washington (Bahder et al. 2013), Oregon (Walton et al. 2013), and California (MacDonald et al. 2021); however, to date there are no reported studies on the use of synthetic sex pheromones for the suppression of Ps. maritimus in a mating disruption program.
Here, we describe field studies directed at the development of a pheromone-based mating disruption strategy for Ps. maritimus. Our primary objective was to determine if placement of pheromone dispensers in vineyards can reduce grape mealybug population density and if so, what perhectare-density of dispensers is required to reduce pheromone trap captures (or bring sentinel trap captures to near zero), as a benchmark to determine sufficient inhibition of Ps. maritimus mating and reproduction.
Materials and Methods
Field test sites and treatment application
Experiments were conducted in commercial vineyards near Paterson, WA (from April/May to October 2021, 2022, and 2023) and Whitstran, WA (from April to October 2022 and 2023). Vineyards were from 4 to 12 ha, mature (>5 yr old), trained to a T-trellis (two or four-wire), drip-irrigated, clean-cultivated, and planted on deep silt-loam over basalt bedrock and gravel. The Paterson vineyard included Merlot, Syrah, Pinot noir, and Sauvignon blanc cultivars and the Whitstran vineyard was a Concord cultivar. Within each vineyard, treatment plot size ranged from 2 to 3.6 ha, and treatments were separated by distances of 2 to 10 ha, or located in different vineyards several kilometers apart. Growers applied standard insecticides in the conventional vineyards to control mealybugs during the study, while no insecticides were applied in the organically certified vineyard.
Pheromone dispensers and deployment rate
Two pheromone dispenser types were deployed: isomate rope (twist-tie) provided by Pacific BioControl Corporation and a CIDETRAK GMB MESO ‘meso’ dispenser provided by Trécé Inc. Both contained synthesized Ps. maritimus sex pheromone (trans-α-necrodyl isobutyrate) and were not commercially available during the study. Each trial used a randomized block design with treatments distributed across the grape cultivars, as described previously. Pacific Biocontrol twist-tie dispensers were deployed at five densities (0, 25, 74, 148, and 247 dispensers per ha), with two replicates in each year from 2021 to 2023. CIDETRAK GMB MESO dispensers were deployed at three density levels (0, 79, and 124 dispensers per ha), with three replicate blocks in both 2022 and 2023.
Adult male flight activity
To monitor mealybug populations, the synthesized sex pheromone for Ps. maritimus was loaded by Trécé into 11-mm gray silicone rubber septa lures (West Pharmaceutical Services) with hexane solutions (25-μg racemic pheromone in 25-μL hexane). From April/May to October of each year, two or three delta sticky traps with a single lure were deployed in each treatment plot, hung in the vineyard canopy. Traps were replaced weekly, while pheromone lures remained in place to monitor adult male flights of Ps. maritimus. Captured adult males were counted at the Environmental and Agricultural Entomology Laboratory (Washington State University Irrigated Agriculture Research and Extension Center) using a Nikon SMZ 1000 stereo zoom microscope.
Results are presented as sample means ± standard error of the mean; all trap counts were converted to adult male mealybugs per trap per week. Data were analyzed using the general linear model function in Systat (ver. 13, Systat Software Inc.), followed by Tukey’s pairwise comparison to separate treatment means. For each dispenser type, data consisted of the average peak flight trap captures for the first (mid-May to mid-June) and second (mid-August through September) Ps. maritimus generations for the meso dispensers in 2022 and 2023 (four treatment replicates) and twist-tie dispensers in 2021, 2022, and 2023 (six treatment replicates).
Results
Male mealybug flight activity
Over the 3-yr study, 2110 pheromone traps were deployed. Counts of adult male Ps. maritimus ranged greatly, from 0 to 911 mealybugs per trap per week. Across all years and dispenser types, two generations per year were observed, each with distinct peak flights, typically between May and June for the first flight and August and September for the second flight (Figure 1). There was annual variation in peak flight periods, with 2022 seasonally later than 2021 and 2023 for both the first and second flights. There was also annual and seasonal variation in mealybug densities, as measured by trap captures, with a higher first flight in 2021 (74.9 ± 17.3) than in 2022 (20.1 ± 5.5) and 2023 (24.5 ± 5.7) (F = 9.821; df = 2,434; p < 0.001), and a higher second flight in 2022 (40.2 ± 5.1) than in 2023 (21.8 ± 3.3), but not different from 2021 (29.5 ± 8.8) (F = 3.420; df = 2,562; p = 0.033).
Average counts (± standard error) of male Pseudococcus maritimus in pheromone-baited traps in pheromone and control vineyards in 2021, 2022, and 2023, showing two flight periods (generations) per year.
Impact of pheromone dispensers
Across both dispenser types and all deployment densities, captures of adult male Ps. maritimus were lower in plots with dispensers than in control plots in each year and generation (Figure 2). Trap counts of adult male mealybugs in the Trécé CIDETRAK GMB MESO dispensers were significantly lower than the control at both 79 and 124 dispensers per ha, but were not different between dispenser densities (F = 14.338; df = 2,9; p = 0.002; Figure 3A). Similarly, trap counts in the Pacific Biocontrol twist-tie dispensers were significantly lower than the control at all deployment densities, but there was no differentiation among deployment density treatments (F = 5.572; df = 2,25; p = 0.002; Figure 3B). For each year and flight combination, there was a pattern of fewer trapped males in pheromone plots, but there was less treatment separation, in part because there were low trap counts in control plots for 2022 first flight and 2023 first and second flights (Figure 3B).
Average number (± standard error) of male Pseudococcus maritimus in pheromone-baited traps is significantly greater in each year and flight period in control plots than in plots receiving Ps. maritimus synthetic sex pheromone released using either CIDETRAK GMB MESO ‘meso’ dispensers or Pacific BioControl isomate rope dispensers in 2021 (first flight: F = 14.560; df = 1,98; p < 0.001; second flight: F = 22.722; df = 1,118; p < 0.001), 2022 (first flight: F = 19.582; df = 1,158; p < 0.001; second flight: F = 20.497; df = 1,238, p < 0.001), and 2023 (first flight: F = 28.584; df = 1,175; p < 0.001; second flight: F = 16.563; df = 1,203; p < 0.00). Different letters above each bar indicate a significant treatment difference.
Average numbers (± standard error) of male Pseudococcus maritimus in pheromone-baited traps are significantly greater in control plots than in plots receiving sex pheromone for A) CIDETRAK GMB MESO ‘meso’ dispenser at deployment rates of 0, 79, and 124 dispensers per ha in 2022 (first flight: F = 5.294; df = 2,77; p = 0.007; second flight: F = 4.232; df = 2,117; p = 0.017) and 2023 (first flight: F = 9.498; df = 2,81; p < 0.001; second flight: F = 12.532; df = 2,98; p < 0.001). Average numbers show a treatment effect for B) Pacific BioControl isomate rope dispenser at deployment rates of 0, 25, 74, 148, and 247 dispensers per ha in 2021 (first flight: F = 3.656; df = 4,95; p = 0.008; second flight: F = 5.791; df = 4,115; p < 0.001), 2022 (first flight: F = 3.164; df = 4,75; p = 0.019; second flight: F = 8.797; df = 4,115; p < 0.001), and 2023 (first flight: F = 3.002; df = 4,88; p = 0.023; second flight: F = 5.546; df = 4,104; p < 0.001), with a pattern of lower trap captures in pheromone plots than in controls. An asterisk near each mean indicates a significant difference from the control. There were no differences among dispenser deployment densities (Tukey’s pairwise comparison, p < 0.05).
Discussion
Our study explored the potential use of synthetic sex pheromone dispensers in a mating disruption program. Previous studies with mating disruption for the vine mealybug (e.g., Cocco et al. 2014, Sharon et al. 2016, Mansour et al. 2017, Daane et al. 2021) helped develop and refine a commercial program for this pest that is now used in vineyards worldwide. We demonstrated that Ps. maritimus has two seasonal flight periods, or two generations per year, as shown previously in Washington (Grimes and Cone 1985, Bahder et al. 2013), Oregon (Walton et al. 2013), and California (Geiger and Daane 2001, MacDonald et al. 2021).
There are two important aspects to this seasonal pattern. First, discrete and relatively short (3 to 4 wk) flight periods provide a better discernible application window. One challenge with initial Pl. ficus programs was developing passive dispensers that would last a long season to cover the four to six generations of this pest, or a 9-mo period of flight activity (e.g., Daane et al. 2020, Mercer et al. 2023). Sprayable formulations are popular, but the microencapsulated formulation typically lasts only 4 to 5 wk, often requiring multiple spray applications for Pl. ficus (e.g., Il’ichev et al. 2006, Walton et al. 2006). Our results suggest that a passive dispenser with a 4- to 5-mo longevity, or two applications of a sprayable formulation applied before the first and second flights, could provide season-long coverage. Second, the seasonal occurrence of each flight period varied by up to 4 wk annually, suggesting that calendar-based pheromone applications would be less effective than approaches guided by pheromone trap monitoring or degree-day models. A similar strategy was proposed previously (Onayemi et al. 2025), with a degree-day model used to recommend late fall insecticide applications for Ps. maritimus, when virus-transmitting nymphs are most susceptible.
Our goal is to develop a mating disruption program for Ps. maritimus, and in this first attempt, we showed that deployment of both twist-tie and meso dispensers lowered trap catches of adult male Ps. maritimus (Figure 2). Other researchers have used pheromone-baited trap catches to indicate population density and mating disruption efficiency: trap captures to determine novel meso dispenser impact on Pl. ficus (Mercer et al. 2023); determining the relationship between Pl. ficus trap captures, mealybug density, and crop damage (Daane et al. 2006, Cocco et al. 2014); and trap captures to determine the impact of pheromone dispenser height-placement on codling moth, Grapholita molesta (de Lame and Gut 2006). Sampling Ps. maritimus is difficult because of their clumped distribution in vineyards (Geiger and Daane 2001), and pheromone traps have been shown to be an effective and far less time-consuming sampling method (Bahder et al. 2013). However, the absence of a direct relationship between mating disruption treatment and Ps. maritimus density is a limitation of this trial. Additionally, the specific pheromone content of each dispenser was not disclosed by the manufacturers due to proprietary restrictions, which limited our ability to relate trap suppression to pheromone dose.
Dispenser density is another aspect of mating disruption programs that can affect both efficacy and economics (Miller and Gut 2015, Mercer et al. 2023). We tested five deployment densities with twist-tie dispensers and two densities with meso dispensers, but while there were fewer Ps. maritimus adult males caught than in the no-dispenser controls, we found no difference among deployment densities (Figure 3). For the meso-dispensers, there were near-zero counts at both deployment densities tested, except for the second flight in 2022 (Figure 3A), arguing that both deployment densities were too high. However, for the twist-ties there was no significant difference from 25 to 247 dispensers per ha. Near-zero adults were caught at the highest dispenser density in all but the first flight in 2021. Nevertheless, there were near-zero trap captures in some trial periods at all densities and, more importantly, there were >20 adult males trapped at the highest deployment rates at 148 dispensers per ha in 2022 (first and second flights) and 2021 (first flight), and at 247 dispensers per ha in 2021 (first flight), suggesting that ‘trap shut down’ was not consistently observed. Some possibilities may account for these inconsistencies. First, producing synthetic trans-α-necrodyl isobutyrate is more complicated than producing the pheromone for mating disruption of Pl. ficus, G. molesta, and other targeted pests. Therefore, production of dispensers each year was limited, leading to smaller plot sizes, later deployment in 2021, and fewer replications than desired. Second, the dispenser emission rate and pheromone load in the dispensers are unknown, which may have affected dispenser efficiency during the second flight. Still, there was a relatively strong treatment effect.
The primary classifications of mating disruption have been divided into competitive and non-competitive categories (Miller and Gut 2015). We expected that mating disruption in our study would fall under the competitive category, where males retain the ability to respond to females and/or traps, and therefore, the degree of pest control is contingent upon pest density or dispenser density. This must still be determined, along with the deployment rate of dispensers needed, which might be an advantage of a sprayable formulation that has more point sources. To date, the synthetic Ps. maritimus pheromone has been used for population monitoring only, while the sex pheromones of other mealybug species have been used for both monitoring and mating disruption (e.g., Walton et al. 2004, 2006, Cocco et al. 2014). For Pl. ficus, the transition from using its sex pheromone for monitoring to mating disruption was relatively fast; however, this same transition has been slower for the Ps. maritimus pheromone, which was identified and synthesized in 2007 (Figadère et al. 2007) and tested for mating disruption nearly 15 yr later. A considerable issue is the large-scale synthesis of trans-α-necrodyl isobutyrate, of which different industry entities are pursuing and improving yearly. This will be a key issue for developing, refining, and commercializing a mating disruption program for Ps. maritimus. The potential use of grape mealybug mating disruption would provide an alternative IPM tool to suppress mealybug densities (Daane et al. 2018, Cocco et al. 2021), thereby slowing the spread of GLRaVs (Almeida et al. 2013).
Conclusion
This is the first report on mating disruption trials for Ps. maritimus using pheromone dispensers. We showed that Ps. maritimus has biological features that are advantageous to a mating disruption program. First, there are discrete and relatively short-lived flight periods, indicating that pheromone application can use passive dispensers with a relatively short field longevity, or sprayable or aerosol formulations with more targeted pheromone release periods. Second, the attraction of Ps. maritimus males to synthetic pheromones appears to be strong and highly competitive, as trap captures, with at times relatively large numbers in the control plots, were made when few live mealybugs could be found through visual searches. Results suggest that this control strategy has potential for development and commercialization. Pheromone dispenser deployment led to a near shutdown of male Ps. maritimus captures, indicating strong mating disruption and potential for reduced pest densities in vineyards. This work is still incomplete, however, as we found no evidence of dispenser density impact on trap captures, and we were unable to associate mealybug population density (other than trap captures) with pheromone deployment. Further studies are needed in vineyards or orchards that have greater pest pressure and, pending improved synthetic pheromone production, work in larger blocks is required.
Data Availability
The data underlying this study are available on request from the corresponding author.
Footnotes
This research was funded by the Washington State Wine Commission Research Grant Programs FY23 Projects and Washington State Department of Agriculture’s Specialty Crop Block grants program. We appreciate the support of Ste. Michelle Wine Estates for providing their vineyards for our study. The authors have no conflict of interest with the work described herein, which was a part of the doctorate thesis for Stephen Onayemi.
Onayemi SO, Daane KM and Walsh DB. 2026. First report of pheromone-based mating disruption for grape mealybug (Pseudococcus maritimus). Am J Enol Vitic 77:0770003. DOI: 10.5344/ajev.2025.25033
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- Received June 2025.
- Accepted November 2025.
- Published online February 2026
This is an open access article distributed under the CC BY 4.0 license.
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