Final report for OS21-147
Project Information
The purpose of this project is to enhance the chemical and mechanical control of ambrosia beetles by developing a “push-pull” system that combines natural repellents and visually and chemically attractive insect traps. A push-pull system combines two forces: an attractant (the pull) and a repellent (the push). An initial push-pull system was tested in avocado by our team and produced encouraging results [4]. The field experiments demonstrated that the combined used of verbenone, an aggregation repellent, and the use of ethanol lures, a volatile highly attractive to the ambrosia beetles, significantly decreased the number of ambrosia beetles landing on traps attached to avocado trees (Riviera et al. 2020). Importantly, we did not capture a single ambrosia beetle in the traps placed on the trunk of the trees exposed to the push-pull treatment. However, the protection was only effective if verbenone was applied on each tree, as the active space around the repellents was less than 1 m. This limitation can be a severe drawback to the widespread use of this method by avocado growers.
It is well known that ambrosia beetles use a combination of odors and visual cues to locate their host. These signals include the shape of the tree, the color of the trunk, and the volatiles emitted by the tree [7,8]. Typically, ambrosia beetles seek out large mature trees emitting some form of stress related volatiles such as ethanol [9]. We conceived mock trees made of cylindrical cardboard covered with a reflective material and associated with a slow-release ethanol lure. Preliminary experiments demonstrated that the addition of a reflective color dramatically increased the attractiveness of these mock trees. We propose to improve the current push-pull system presented in Rivera et al. [4] with the use of our enhanced mock-trees. We will investigate specific questions relevant for growers to apply this system in their grove. Specifically, we will investigate 1) to what distance mock-trees should be placed to attract the most beetles and 2) the density of mock-trees and repellent per block to obtain the best and most cost-effective protection of avocado trees.
Objective 1: Mock-trees will be placed within, on the edge, and outside the avocado grove. White sticky traps will be attached to each mock-tree to trap adult beetles that land on them. White sticky traps will be placed on live asymptomatic avocado trees within the first and second row of the grove to serve as the treatment control. Mock-trees and white sticky traps will be spaced at a distance equivalent to four avocado rows in the grove. Beetles will be collected from the traps every 14 days and shipped to the NFREC in Quincy to be counted and identified at the species level. Beetles will be identified to species based on more recent identification keys for ambrosia beetles in Florida. The mock-trees will consist of a cylindrical cardboard tube with an 8-inch diameter, covered in a reflective mulch, emitting various spectrums of light. We obtained preliminary data showing that reflective material was the most attractive to ambrosia beetles present in avocado grove as compared to white or blue color. A slow-release lure of ethanol (Evergreen Growers Supply) will be placed on each mock-tree. Our preliminary data demonstrated that the addition of ethanol lures significantly increased the attractiveness of the mock-trees.
Treatment 1: Control sticky trap on avocado tree.
Treatment 2: mock-trees with ethanol lure and sticky trap within the interior of the avocado grove
Treatment 3: mock-trees with ethanol lure and sticky trap on the edge (<5 m) of the avocado grove
Treatment 4: mock-trees with ethanol lure and sticky trap outside the avocado grove, 10 meters from the first row of trees.
The avocado grove will be divided in 5 blocks of equal size, and the five treatments will be replicated in a generalized randomized block design. The number of beetles captured on each treatment will be compared with ANOVA for normally distributed data or a generalized linear model using Poisson distribution if the data are Poisson distributed. In addition, a principal component analysis will be used to determine the profile of the ambrosia beetle community attracted by the mock-trees disposed at the different distance from the avocado grove.
Objective 2 will consist of a complete push/pull system combining the mock-trees + ethanol lures (‘pull’) from objective 1 with the application of verbenone on the trunks of avocado trees as the repellent (‘push’). Data from objective 1 will be used to determine the optimal placement of the mock-trees relative to the avocado border. Push treatments will consist of repellent formulations of Verbenone SPLAT® (ISCA technology, Riverside CA) provided in caulking tubes. Typically, Verbenone SPLAT is applied directly on the trunk around the circumference of the tree at 1 – 1.5 meters above ground level. For this experiment, two concentrations of verbenone will be tested 1) four 17.5 g dollops of Verbenone SPLAT, measuring 2 cm in diameter and totaling 70 g per tree on each tree in the plot (high rate) and 2) four 17.5 g dollops of Verbenone SPLAT, measuring 2 cm in diameter and totaling 70 g per tree on one tree out of two in the plot (low rate). Pull treatments will consist of visual targets + ethanol lures (cf. objective 1). Two densities of visual targets will be tested 1) a ratio of 1 visual target for 1 avocado row and 2) a ratio of 1 visual target for 2 avocado rows. Push-pull treatments will consist of both SPLAT application on the avocado trees and the visual targets on the border of the plot. The following treatments will be tested: 1) untreated control, 2) low verbenone rate, 3) high verbenone rate, 4) low verbenone rate + low trap density, 5) high verbenone rate + low trap density, 6) low verbenone rate + high trap density, and 7) high verbenone rate + high trap density.
The rate of 70g of verbenone per tree is based on our previous trial demonstrating that this rate significantly decreased the number of beetles in the push-pull treatment [4]. We hypothesize that the addition of visual targets will increase the efficacy of our system and will reduce the amount of verbenone needed to obtain a significant reduction of ambrosia beetles. Plots will be a 6 x 6 square of avocado trees separated with one buffer row. The field will be organized with a split-plot design with trap treatments as the whole plot factor and the verbenone as the split-plot treatment. Plots will be disposed on the border of the grove so the visual targets can be disposed in front of each plot. White 15 x 18 cm sticky cards will be attached to three trees per plot at approximately 1.5 meters from the base of the tree. Push-pull treatments will have sticky card traps attached at 1.5 meters on trees in between the splat; traps for untreated controls will be attached in approximately the same location. Traps will be placed on the central 16 trees within each plot. There will be four replicates per treatment. Ambrosia beetles will be collected from sticky card traps biweekly and sent to Quincy for identification. Collected ambrosia beetles will be examined visually and under a microscope for the presence of select species and other ambrosia beetle species. Ambrosia beetle species in the tribe Xyleborini will be identified using the key published in Gomez et al. (2018) [10]. The number of ambrosia beetles for each species will be compared across treatments with appropriate mixed model analyses using either an ANOVA for normally distributed data or a generalized linear model using Poisson distribution if the data are Poisson distributed.
Cooperators
- - Producer
Research
2021 Field trial
In summer 2021, teams from the UF/IFAS North Florida Research and Education Center (NFREC), the Citrus Research and Education Center (CREC) and the Tropical Research and Education Center (TREC) conducted a push-pull experiment to control ambrosia beetles in avocado groves. The ‘Push-Pull’ system combines a repellent force and an attractant force and aims to obtain an additive or synergetic effects between the two forces. In this experiment, a SPLAT mixture of verbenone and methyl-salicylate was used as repellent (‘Push’), and silver colored tubes (Fig. 2) baited with ethanol as attractant (‘Pull’). The silver-colored tube traps consisted of an 8 inches diameter cardboard tube wrapped in a colored reflective plastic (UV). The traps were baited with ethanol volatile lures; those ethanol dispensers mimic stressed and declining trees and are attractive to a broad range of species of ambrosia beetles in avocado. In the first experiment, silver-colored tube traps were placed at different locations from the avocado edge, to reduce landing rates of ambrosia beetles on avocado trees: 1) Control sticky trap on avocado tree, 2) mock-trees with ethanol lure and sticky trap within the interior of the avocado grove, 3) mock-trees with ethanol lure and sticky trap on the edge (< 5 m) of the avocado grove, 4) mock-trees with ethanol lure and sticky trap outside the avocado grove, 10 m from the first row of trees.
The four treatments were broken up into blocks and distributed randomly in the rows of the trees. The silver-colored tubes were attached with a superficial strip of reflective material which was coated with insect adhesive to trap and ambrosia beetles that landed on the trap. The adhesive strips were collected every two weeks. Each block consisted of 16 avocados, and in each block the six avocado trees situated in the center of the block will be used for the experiments. Three of those trees had a 14-17 g dollop SPLAT-verbenone applied to it and three would stay untreated. was applied to the selected treatment trees.
A white 23 x 28 cm sticky card (Wing Trap Liners IPM-103, Great Lakes IPM, Vestaburg, MI, USA) was stapled in a randomized direction directly above or below the SPLAT application approximately 1.5 m from ground level and replaced approximately every 2 weeks. Traps for both negative control groups were attached in approximately the same location. Sticky traps and silver colored tubes were examined visually and under a microscope for the presence of ambrosia beetles. Ambrosia beetles were identified to species level.
2022 Trial.
In summer 2022, the experiment consisted of a push-pull design with silver-colored tubes placed on the outside of the grove using two different amounts of SPLAT beetle guard. The placement of the silver-colored tubes was determined based on the results from the experiment conducted in 2021. This edge of plot borders faced the unmanaged avocado and one uncultivated open field on the west side of the study area. Treatments were applied in a randomized complete block design with five treatments per block: 1) four dollops of beetle guards, 2) eight dollops of beetle guards, 3) four dollops of beetle guards with a visual trap, 4) eight dollops of beetle guard and a visual trap and 5) untreated control and four replicates per treatment. Replicate blocks were separated by at two rows or more of avocado and treatment plots were separated by two rows of avocado. Six white unbaited sticky traps were stapled onto a tree 1-1.5 m above the ground in each replicate block with three traps on trees treated with SPLAT and three untreated trees. Traps were placed ~5–10 cm away from SPLAT dispensers (termed ‘close’). Traps were collected and replaced in the field once a month for 3 months. All ambrosia beetles caught on the sticky traps were counted, regardless of species. All Scolytidae beetles were identified to species level with the use of the most recent taxonomic key. Voucher specimens are kept in the laboratory at the North Florida Research and Education Center in Quincy, FL, USA.
Beetles captured were classified as either Rafaella lauricola (RL) carrier, or non-RL carrier (Carrillo et al., 2014; Ploetz et al., 2017). RL carrier beetles captured included Xyleborus volvulus, X. ferrugineus, X. affinis. Xyleborinus saxesenii and X crassiusculus were also included despite behind poor vector of RL. Non-RL beetles included Xyleborus pubescens, X. impressus, E. fornicatus, Ambrosiodmus devexlus and A. leconti. Only a little number of RL beetles were captured on untreated control (n=4); therefore, the analyze were done on the whole beetle count.
The only treatment that differed significantly was when the traps were placed outside with the SPLAT treatment (-60.1%). Other treatment showed no difference as compared to the control (Fig. 3).
Carrillo, D., Duncan, R. E., Ploetz, J. N., Campbell, A. F., Ploetz, R. C., & Peña, J. E. (2014). Lateral transfer of a phytopathogenic symbiont among native and exotic ambrosia beetles. Plant Pathology, 63(1), 54–62. https://doi.org/10.1111/ppa.12073
Ploetz, R. C., Konkol, J. L., Narvaez, T., Duncan, R. E., Saucedo, R. J., Campbell, A., Mantilla, J., Carrillo, D., & Kendra, P. E. (2017). Presence and Prevalence of Raffaelea lauricola , Cause of Laurel Wilt, in Different Species of Ambrosia Beetle in Florida, USA. Journal of Economic Entomology, 110(2), 347–354. https://doi.org/10.1093/jee/tow292
Field trial 2022.
Beetles captured were classified as either Rafaella lauricola (RL) carrier, or non-RL carrier (Carrillo et al., 2014; Ploetz et al., 2017). RL carrier beetles captured included Xyleborus volvulus, X. ferrugineus, X. affinis, X. bispinatus. Xyleborinus saxesenii and X crassiusculus were also included despite behind poor vector of RL. Non-RL beetles included Xyleborus pubescens, X. impressus, X. intrusis, E. fornicatus, Ambrosiodmus devexlus and A. leconti.
We captured significantly less beetles on trees treated with SPLAT than on trees in the control plots (-70.8%) or on trees in treatment plot but that did not receive the SPLAT treatment directly (-79.6%). For trees treated directly with SPLAT Push treatment with four dollops and the two push-pull treatments with eight and four dollops had significantly less beetles than the control. Surprisingly, the push treatment with eight dollops did not have a significant decrease in the number of beetles captured as compared to the control group (Fig. 4).
Educational & Outreach Activities
Participation Summary:
List of on farm demonstration:
- Conover D, Martini X. Demonstration. Demonstration of SPLAT use and laurel wilt control. Broward County. May 10, 2022. 5 attendees.
- Conover D, Martini X. Demonstration. Demonstration of SPLAT use and laurel wilt control. Broward County. March 23, 2021. 7 attendees.
List of Webinars, talks and presentations.
- Conover D, Martini X., Evaluation of semiochemical and visual based push-pull strategy for managing redbay ambrosia beetle on redbay. Southeastern Branch of the Entomological Society of America. Little Rock AR. March 12-14, 2023
- Conover D, Martini X. Evaluation of visual based trapping methods for ambrosia beetles associated with laurel wilt. 2022 ESA, ESC, and ESBC Joint Annual Meeting. Vancouver, BC. November 13-16, 2022.
- Martini X, Conover D, Rivera M, Stelinski LL. Symposium. Control of ambrosia beetles and laurel wilt with repellents in forest systems and avocado groves. Annual Meeting of the Entomological Society of America. Denver, CO. Oct. 31- Nov. 3, 2021.
- Martini X, Stelinski LL, Carrillo D, Conover Dg. Symposium. Use of semiochemical and visual cues to control ambrosia beetles and laurel wilt spread. International Congress of Entomology. Helsinki, Finland. July 17- 22 2022.
List of Published press articles, newsletters
- Martini X., Sprague D, Conover D.(2023)Managing ambrosia beetles in citrus and other fruit trees. Panhandle Ag e-News. https://nwdistrict.ifas.ufl.edu/phag/2023/04/28/managing-ambrosia-beetles-in-citrus-and-other-fruit-trees
- Martini X., Sprague D, Conover D.(2023) Managing Ambrosia Beetles in Cold Hardy Citrus. Cold Hardy Citrus Connection. 4: 2-4.
One Journal article in preparation:
1. Conover D., Carrillo D., Stelinski LL, Martini X. Control of ambrosia beetle in Avocado with the use of a push pull system using verbenone and attractive visual cues. To be submitted in Pest Management Science.
Learning Outcomes
Consider using repellent once the product will be commercialized.
Project Outcomes
This project ended with very positive outcome for the control of ambrosia beetle in avocado without relying on conventional insecticides. With the use of an attractive trap, and an active repellent (compatible with organic practices) we reduced significantly and consistently the number of beetles carrying the fungi Raffaelea lauricola in avocado. As the efficacy of this system has been demonstrated during two consecutive seasons, we hope that through our Extension efforts, more growers will adopt this strategy to protect their trees against ambrosia beetles and laurel wilt and significantly reduce their insecticide use. This strategy could save thousands of avocado trees, reduce pollution and unwanted side effects of insecticide and increase farm profitability. It also brings control methods for organic avocado growers.
Our work demonstrated that for this strategy to be efficient, either every tree should be treated with SPLAT repellent (or any other verbenone-based repellent), or only one tree out of two, but in this case attractive silver traps should be disposed outside the grove at a distance where reinfestation of the grove by beetles attracted by the UV reflectance will be unlikely.