Wigging out, then wigging in: removing earwigs from stone fruit and augmenting them in pome fruit

Progress report for SW20-916

Project Type: Research and Education
Funds awarded in 2020: $348,733.00
Projected End Date: 12/31/2023
Host Institution Award ID: G361-20-W7899
Grant Recipients: USDA-ARS; Washington State University; Oregon State University; M3 Consulting
Region: Western
State: Washington
Principal Investigator:
Co-Investigators:
Rick Hilton
Oregon State University
Nathan Moses-Gonzales
M3 Consulting Group
Dr. Louis Nottingham
Washington State University
Dr. Ashley Thompson
Oregon State University
Dr. Northfield Tobin
Washington State University
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Project Information

Summary:

Current research indicates that earwigs are critical natural enemies of aphids, pear psylla, and codling moth. However, the role of earwigs in controlling orchard pests has been unappreciated, likely because previous pesticide programs were too harsh for earwigs to thrive. Growers that recently converted to softer programs have been unable to use earwig biological control because their populations have been eliminated; earwigs have long generation times and poor dispersal ability, which inhibits their reestablishment. This project will develop tactics that growers can use to inoculate their orchards with earwigs. Earwigs are particularly good candidates for inoculation because they are omnivorous and poor dispersers, so they often remain in orchards feeding on alternative food when pest populations are low. This is in contrast to other natural enemies (e.g. ladybeetles and lacewings) that readily move out of orchards after release, especially if prey populations are low. We will create a mass-trapping protocol for earwigs to support releases in pome fruit by determining (a) the most effective mass trap and (b) whether these traps can be used to reduce damage in stone fruit, where earwigs are pests. The project will examine the potential of earwig augmentation in pome fruit by (a) confirming that earwigs do not damage pears or ‘Honeycrisp’ apples, (b) determining optimal earwig release rates and timings for establishment, (c) examining efficacy of using earwig shelters to increase earwig populations, and (d) testing the potential of drones as a more efficient method of earwig release. We will also screen pesticide non-target effects on earwigs so growers can make spray choices that minimize harm to biocontrol agents. We will improve stakeholder knowledge regarding earwig IPM by (a) summarizing research findings at grower meetings, (b) conducting field days on collaborating grower farms, and (c) creating extension documents and (d) a multimedia library describing earwig biology and management. Our project will reduce orchardist reliance on insecticides to manage pests, decreasing pesticide exposure of workers, consumers, and the environment.

Project Objectives:

1. Develop a mass trapping protocol for earwigs to support releases in pome fruit by removing them from stone fruit orchards where they are pests. (Years 1-2)

a. Determine which trap type catches the largest number of earwigs in stone fruit orchards

b. Measure success of earwig mass trapping in stone fruit orchards

2. Examine potential of earwig augmentation in pome fruit.

a. Determine if earwigs cause damage to pears or to ‘Honeycrisp’ or ‘Gala’ apples (Year 1)

b. Determine optimal release rates and timing to establish augmented earwigs (Years 1-3)

c. Examine the efficacy of adding shelters to increase abundance of existing earwig populations (Years 2-3)

d. Test potential of using drones to release earwigs (Years 2-3)

3. Screen non-target effects of pesticides on earwigs. (Years 2-3)

a. Determine acute short-term toxicity of organic and conventional tree fruit pesticides to earwigs

b. Examine sublethal effects of pesticides on earwig motor coordination and predation

4. Improve stakeholder knowledge on earwig IPM.

a. Summarize research findings at grower meetings (Years 2-3)

b. Conduct field days on collaborating grower farms to demonstrate earwig monitoring and effects on pest populations (Year 2)

c. Create widely available extension documents describing earwig biology, monitoring, and augmentation (Years 1-3)

d. Create an online video and photo library to convey project results and demonstrate earwig trapping and augmentation (Years 1-3)

e. Measure changes in grower knowledge with surveys throughout the project (Years 1-3)

Timeline:

Please view the attached Gantt chart for the timeline (Excel version). It can also be viewed in the image below. For in-orchard work, the grower collaborators associated with each group are Nick Willett (Wapato/Yakima), Floyd Stutzman (Wenatchee), and Steve Hunt (Hood River). The research/educator leaders for each group are Rebecca Schmidt-Jeffris (Wapato), Louis Nottingham and Tobin Northfield (Wenatchee), Ashley Thompson (Hood River), Rick Hilton (Medford), James Hagler (Maricopa), Nathan Moses-Gonzalez (M3 Consulting).

Timeline

Timeline of grant activities.

Cooperators

Click linked name(s) to expand/collapse or show everyone's info
  • Dr. James Hagler (Researcher)
  • Steve Hunt - Producer
  • Floyd Stutzman - Producer
  • Nick Willett - Producer

Research

Hypothesis:

Experimental hypothesis for each objective

Develop a mass trapping protocol for earwigs to support releases in pome fruit by removing them from stone fruit orchards where they are pests.

Determine which trap type catches the largest number of earwigs in stone fruit orchards

H: Larger traps in protective plastic that have been left in the orchard for a longer period of time will catch the most earwigs

Measure success of earwig mass trapping in stone fruit orchards

H: Removal of earwigs from stone fruit orchards will decrease damaged fruit

Examine potential of earwig augmentation in pome fruit.

Determine if earwigs cause damage to pears or to ‘Honeycrisp’ or ‘Gala’ apples

H: Earwigs will only cause damage to pears and apples if they are not provided with other food sources

Determine optimal release rates and timing to establish augmented earwigs

H: At least one release rate or timing will show increased earwig abundance and reduced pest numbers compared to the no-release control

Examine the efficacy of adding shelters to increase abundance of existing earwig populations

H: Plots with shelters will have higher earwig counts than those without shelters

Test potential of using drones to release earwigs

H: Earwigs released by drone will be recovered after release at the same rate as those released by hand

Screen non-target effects of pesticides on earwigs

Determine acute short-term toxicity of organic and conventional tree fruit pesticides to earwigs

H: Some pesticides will increase earwig mortality

Examine sublethal effects of pesticides on earwig motor coordination and predation

H: Some pesticides will alter earwig movement patterns and predation rates

Materials and methods:
 

Methods for work completed in 2021 (Year 1) shown below. We were unable to start work in 2020 due to COVID-19 restrictions. Work on objectives not listed here is scheduled to begin in 2022. With 2021 as our Year 1, all work is currently on schedule with the exception of Objective 2a (Determine if earwigs cause damage to pears or to ‘Honeycrisp’ or ‘Gala’ apples). This subobjective is being altered based on feedback from cooperating growers who would like us to focus exclusively on 'Honeycrisp' and use several additional testing conditions to determine the ability of earwigs to cause damage. We will be finalizing those methods over the summer and conducting the research in the fall when 'Honeycrisp' apples are available on trees in the field.

Objective 1A – Testing different types of trap to improve earwig capture

To determine if different designs of the commonly used cardboard rolled strip might capture more earwigs, we conducted field trials in stone fruit orchards in three different locations and time periods (Table 1). Each individual tree contained one trap attached slightly under the tree crotch using flagging tape. Using a completely randomized experimental design, four different types of traps were tested across the three field trials, with an extra treatment being tested in only one orchard (Table 2). For each field trial, the number of earwigs per trap was counted weekly by blowing air into traps and counting earwigs that fell out of the trap into a bucket. After counting, earwigs were removed from the field and taken back to the laboratory for use in other experiments.

Study location Crop Sampling period
Yakima, WA Cherries 22 Jun-3 Aug 2021
Wenatchee, WA Peaches 28 May-9 July 2021
Medford, OR Peaches 11 May - 17 Sep 2021

Table 1. Locations and sampling information for earwig trap testing.

Treatment

Replicates

Trap changing frequency

Locations

Standard cardboard rolled strip (10x30cm)

20-26

Monthly or when damaged

Yakima, Wenatchee, Medford

Standard cardboard rolled strip (10x30cm)

20-26

Weekly

Yakima, Wenatchee, Medford

Soda shelter (0.5L) + 1 standard cardboard rolled strip (10x30cm)

20-26

Monthly or when damaged

Yakima, Wenatchee, Medford

Soda shelter (0.5L) + 1 standard cardboard rolled strip (10x30cm)

20-26

Weekly

Yakima, Wenatchee, Medford

Soda shelter (2L) + 4 standard cardboard rolled strips (10x30cm)

13

Monthly or when damaged

Yakima

The data were analyzed using a linear mixed effects model (LME) using the package lme4 (Bates et al. 2015), with treatment and time (and their interaction) as fixed factors and replicate as a random factor. All data analysis was conducted using the software R, version 4.1.2 (R Core Team 2021).

Objective 1B – Mass trapping earwigs where they are pests: does it help reduce earwig populations and fruit damage?

Mass removal of earwigs

To determine if mass removing earwigs from orchards reduced their populations over time, we monitored and captured earwigs using standard cardboard traps (Fig. 1). The experiments were conducted in commercial nectarine and cherry orchards, located respectively in Yakima and Benton County, Washington State. The experiment consisted of six and five 16-tree (4x4) replicates on nectarines and cherries, respectively. Each individual tree contained one cardboard trap attached slightly under the tree crotch using flagging tape. Each replicate was spaced 30m from each other to account for possible within-season dispersal of earwigs. We had two treatments: a control where earwigs were counted weekly and returned to their respective trees, and a removal treatment where earwigs were counted weekly and removed from the orchard. Weekly sampling went from May 25th to August 9th, 2021, and was always performed during the morning.

cardboard trap
Fig. 1. Standard cardboard rolled strip trap design

The data were analyzed using a linear mixed effects model (LME) using the package lme4 (Bates et al. 2015), with treatment and time (and their interaction) as fixed factors and replicate as a random factor. All data analysis was conducted using the software R, version 4.1.2 (R Core Team 2021).

Earwig damage

To determine if mass removing earwigs from stone fruit orchards reduced fruit damage, we sampled fruits on June 16th and 22nd 2021 for nectarines and cherries respectively, during harvest time, in the same orchards used in the mass trapping experiment. We sampled 32 nectarine fruits (2 per tree whenever possible) and 64 cherry fruits (4 per tree) and visually assessed possible earwig damage (Fig. 2.).

cherry and nectarine fruits with insect chew holes
Fig 2. Possible earwig damage on cherry and nectarine

The data were analyzed using a generalized linear mixed model (GLMM) using the package lme4 (Bates et al. 2015), with treatment as a fixed factor and replicate as a random factor, with a binomial error distribution. All data analysis was conducted using the software R, version 4.1.2 (R Core Team 2021).

Objective 2B – Augmentation of earwigs in pome fruit: can we increase earwig populations and reduce pest pressure?

Methods

Field sites and experimental design

To determine if introducing earwigs in pome fruit orchards increase their population over time, and if this reduced target pest populations, we mass released and monitored earwigs using standard cardboard traps (Fig. 1). The experiments were conducted in commercial apple and pear orchards in Yakima County, Washington State. The experiment consisted of five replicates, each consisting of a release area with 9 trees (3x3), an intermediate area (6 trees in line, starting from the release area), and a 9-tree control area (3x3) (Fig. 3). Each replicate was distant 30m from each other to account for possible within-season dispersal of earwigs (Moerkens et al. 2010). Earwigs were always released in the middle tree of the release area. We had two treatments: a continuous release, where we released 100 earwigs every other week during the season, and a mass release of 500 earwigs done early in the season.

plot design
Fig. 3. Design of each replicate containing release, intermediate, and control areas.

Earwig monitoring

Each individual tree contained one cardboard trap attached slightly under the tree crotch using flagging tape and were monitored once a month. Traps were replaced only if lost or destroyed (e.g., hit by sprinklers or machinery). Traps were checked by blowing air into the traps and subsequently counting earwigs in a bucket and returning them to the same tree. Monthly sampling of earwigs went from June 17th to August 16th, 2021.

Pest monitoring

We monitored apple and pear orchards for the presence and abundance of different target pest species. For apples, we visually monitored the number of leaves infested with woolly apple aphids, rosy apple aphids, and green apple aphids, every other week starting on June 21st through August 16th, 2021. For pears, we collected 27 leaf samples per plot on both control and release areas every other week starting on June 17th through August 10th, 2021. Leaf samples were pooled in paper bags, tagged, and taken back to the lab for processing. All pooled leaves were processed using a leaf brush onto a glass plate containing soap. Subsequently, we counted the number of pear psylla (eggs, small nymphs, and large nymphs), two-spotted spider mites (eggs and motiles), brown mites (eggs and motiles), European red mites (eggs and motiles), and pear rust mites.

Statistical analysis

Preliminary data was analyzed using a generalized linear mixed model (GLMM) using the package glmmTMB (Brooks et al. 2017), with treatment and area (and their interaction) as fixed factors, and replicate and time as random factors, with a negative binomial distribution. All data analysis was conducted using the software R, version 4.1.2 (R Core Team 2021).

Research results and discussion:

Objective 1A – Testing different types of trap to improve earwig capture

Significant findings

  • Standard cardboard traps captured the most earwigs
  • Leaving the traps throughout the season increased the number of earwigs captured in one of the three field sites tested
  • Field trials will continue in the following season to investigate if the aggregation pheromone influence or not earwig catch

Results and Discussion

We found that standard cardboard traps captured more earwigs than 0.5L and 2L soda shelter traps at all locations (Fig. 4). Changing the trap only monthly or when damaged increased the number of earwigs captured only in one of our locations , compared to a weekly change of standard cardboard traps (Fig. 4, Yakima). These results might be related to the accumulation of aggregation pheromones or cuticular hydrocarbons (Quarrell et al. 2016) within the trap throughout the season, although there were no differences between treatments in the other two locations (Fig 4. Wenatchee, Medford). This experiment will be repeated in the next season to further evaluate possible differences between the two standard cardboard trap treatments. This experiment will continue in the following year to further evaluate differences between leaving standard cardboard traps throughout the season or changing them weekly.

graph of earwigs captured per trap type in three locations
Fig. 4. Average number of earwigs captured per trap in a) Cherries in Yakima, and b) Peaches in Wenatchee and c) Medford.

Objective 1B – Mass trapping earwigs where they are pests: does it help reduce earwig populations and fruit damage?

Significant findings

  • Mass removal of earwigs in stone fruit did not significantly reduce earwig populations. However, a trend of reduction over time was observed
  • Removal of earwigs reduced the observed earwig damage on apricots, but not on cherry
  • This study will continue in the following season to further investigate earwig mass trapping effects on their density over multiple seasons

Results and Discussion

We found that mass trapping and removing earwigs from stone fruit orchards did not significantly reduce earwig populations over time. However, we did notice a trend in population declining when comparing removal to control treatments (Fig. 5). These results are promising as earwig mass removing is a multi-year project as initial populations (e.g., after overwintering) are critical to determine season long population dynamics. This experiment will continue in the following year to further investigate if we can reduce earwig populations through mass trapping them in subsequent seasons.

Mass removal of earwigs reduced possible earwig damage on apricots but not on cherries (Fig. 6). This result can be related to the relative higher abundance of earwigs in our cherry orchard compared to the nectarine orchard, also to the ease of earwigs damaging cherry fruits compared to nectarine (Orpet et al. 2019). This experiment will continue in the following year to further evaluate if removing earwigs reduces fruit damage over different seasons.

Figure 5
Fig. 5. Average number of earwigs captured per replicate (sum of 16 traps in 16 trees) over time. n.s. = non-significant difference at p<0.05 (LME).
Figure 6
Fig. 6. Percent of a) apricot and b) cherry fruits showing symptoms of possible earwig feeding. Treatments with an asterisk differ significantly at p<0.05 (GLMM). n.s. = non-significant.

Objective 2B – Augmentation of earwigs in pome fruit: can we increase earwig populations and reduce pest pressure?

Significant findings

  • Augmentation of earwigs during only one season did not provide enough evidence for improved earwig establishment or pest control
  • This study will continue to further evaluate the effect of earwig augmentation over multiple seasons

Results and Discussion

Due to the short duration of the field season, and few sampling dates, it is still inconclusive if mass releasing earwigs increased their populations over time, or if this affects target pest populations. This experiment will continue in the following years in the same location to monitor pest and earwig populations. Shown below are the overall number of earwigs per replicate in apples (Fig. 7), the latter highlighting the high variability in earwig counts per replicate throughout the season. We hypothesize that this high variability might be due to the growing system (trellised apple) and proximity of trees within the same row, versus between rows. This spacing could cause individual trees within a plot to have high variability in earwig counts.  Pest populations were not reduced following release (woolly apple aphid , green apple aphid, and rosy apple aphid).

Figure 7
Figure 7. Average number of earwigs per replicate (sum of 9 traps in 9 trees) throughout the season.

Shown below are the overall number of earwigs per replicate in pears (Fig. 8), the latter highlighting a lower variability in earwig counts per replicate throughout the season, especially when compared to apples. We hypothesize that the lower variability in pears when compared to apples might be due to the different growing system as this a traditional pear orchard with trees being 6m away from each other, thus reducing earwig movement within the row and therefore variability within a plot. Pest populations were not reduced following release (pear psylla, spider mites).

Figure 8
Fig. 8. Average number of earwigs per replicate (sum of 9 traps in 9 trees) throughout the season.

We suspect more than one season of releases is needed to see significant differences in earwig populations and pest control levels. This is because earwigs only reproduce once per year. We will continue monitoring plots where releases occurred in 2021 to determine if next-season pest control is established.

Participation Summary
7 Producers participating in research

Research Outcomes

3 Grants received that built upon this project
18 New working collaborations

Education and Outreach

25 Consultations
1 On-farm demonstrations
1 Published press articles, newsletters
11 Webinars / talks / presentations
5 Other educational activities: Biological control stakeholder focus groups (1.5-3 h) held in Wenatchee, Yakima, and Okanogan (WA) and Medford and Hood River (OR). Earwigs as biological control agents were included in each discussion. Over 60 participants, which included growers, crop consultants, and extension specialists.

Participation Summary:

45 Farmers participated
60 Ag professionals participated
Education and outreach methods and analyses:

Completed Outreach

On-farm demonstrations:

Earwig release study site was used as a stop on the Pear Field Day in southern Oregon. Pear psylla biological control and the potential of earwigs as natural enemies was discussed. The use of rolled cardboard traps was demonstrated.

Webinars/talks/presentations:

Orpet, RJ, and L Nottingham. 2021. Integrating European earwig inoculation with spray programs for pear psylla pest management in commercial orchards. Entomological Society of America National Meeting in Denver, CO.

Orpet, RJ and ST DuPont. 2021. Scouting for integrated pest management in pear in the field. North Central Washington Fieldmen Association meeting, Jun 17.

Orpet, RJ. 2021. Phenology models and other best practices for tree fruit pest management. Washington State Department of Agriculture Pesticide Stewardship Program Workshop, Mar 18 (Cashmere) and Mar 19 (Okanogan) (virtual).

Orpet, RJ and L Nottingham. 2021. Integrated pear psylla management: biological, cultural, and chemical. Medford (OR) Pear Growers Meeting, Jan 28 (virtual).

Orpet, RJ and L Nottingham. 2021. Suppressing pear psylla while conserving natural enemies is the key to success. Wilbur Ellis Washington Grower Meeting, Jan 7 (virtual).

Schmidt-Jeffris. Recruiting and retaining arthropod allies for pest control in tree fruit. University of North Florida. 1 October 2021, Virtual.

Schmidt-Jeffris. Save what you have, add some more if you don’t have enough: conserving and augmenting natural enemies in tree fruit. University of Nebraska-Lincoln. 24 September 2021, Virtual.

Hanel, A., Orpet, R., Hilton, R., Nottingham, L., R. Schmidt-Jeffris, R. Earwigs as Biological Control Agents in Temperate Tree Fruit Orchards: What Do We Know and What is the Way Forward. 95th Annual Orchard Pest and Disease Management Conference, 12-14 January 2021, Portland, OR.

Hanel, A., Orpet, R., Hilton, R., Nottingham, L., Schmidt-Jeffris, R. Does mass trapping earwigs in stone fruit orchards affect yield and fruit damage? Entomological Society of America 69th Annual Meeting, 31 October-3 November 2021, Denver, CO.

Hanel, A., Orpet, R., Hilton, R., Nottingham, L., Schmidt-Jeffris, R. Back to basics: the dual role of earwigs in tree fruit orchards. Pacific Branch - Entomological Society of America Annual Meeting, 10-13 April 2022, Santa Rosa, CA.

Other educational activities:

Biological control stakeholder focus groups held in Wenatchee, Yakima, and Okanogan (WA) and Medford and Hood River (OR). Earwigs as biological control agents were mentioned in each discussion. Over 60 participants, which included growers, crop consultants, and extension specialists.

Outreach in Progress

  • One peer-reviewed publication currently in progress (Orpet)
  • One field tour to be held 8-10 May 2022, sponsored by the Entomological Society of America and led by Schmidt-Jeffris. 55 attendees will include entomologists, orchardists, viticulturists, beneficial insect producers, and crop consultants. The group will discuss the future of biocontrol in perennial crops and include using earwigs as part of the discussion.
  • A feature on the earwig project is planned by a writer at the Good Fruit Grower magazine for some time this summer
  • All collaborators plan to discuss earwig research at one or more of the winter grower meetings this coming year
3 Farmers changed or adopted a practice

Education and Outreach Outcomes

25 Producers reported gaining knowledge, attitude, skills and/or awareness as a result of the project
Key areas taught:
  • The role of earwigs in orchard pest management
  • How to monitor for earwigs

Success Stories

    Success stories:

    One of our participating growers (Bear Creek Orchards, the largest pear and peach grower in Southern Oregon) is planning to conduct their own trap and release program this upcoming season. They will be trapping earwigs in peach orchards and releasing them in pear orchards.

    Another grower in Wenatchee Valley is conducting releases of earwigs in his pears as a result of hearing about this project.

     

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.