Performing Department
(N/A)
Non Technical Summary
Colorado potato beetle is a major pest of potato that has evolved resistance to most pesticides, spurring the search for alternative management strategies such as biological control. An important component of the predator effect on prey is the "non-consumptive effect", which occurs when prey detect and avoid predation using costly responses. This has been shown to reduce pest numbers and protect plants from damage in many cropping systems. Non-consumptive effects represent a novel tactic for pest management, but not being able to trigger prey responses in the absence of live predators has limited their use. We have found that we can elicit non-consumptive effects in Colorado potato beetle by releasing the pheromone of the predaceous spined soldier bug Podisus maculiventris, and in field trials we find this to reduce beetle abundance and plant damage, and to increase potato tuber yield. In addition, the Colorado potato beetle aggregation pheromone has recently been synthesized, and is highly attractive to both male and female beetles. Critical to developing a dual "attractant-deterrent" management system using these two pheromones is understanding 1) their community wide effects on other pests and beneficials and 2) the most effective spatial scales for their deployment. Because both pheromones can be synthetically produced, they can more easily be deployed in the field and they have the potential to facilitate a healthier and more sustainable vegetable production system. This project supports the "Pests and Beneficial Species in Agricultural Production Systems" program priority of innovative biologically based strategies to manage pests.
Animal Health Component
(N/A)
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
Biological control is a mainstay of integrated pest management. However, deploying live natural enemies can be expensive and may yield inconsistent results. Recent advances in our understanding of prey responses to predator cues from a wide range of pest systems opens up new approaches for protecting plants using attributes of traditional biological control. Non-consumptive effects of predators on prey are changes in prey behavior, physiology or life-history that occur when prey detect, but are not consumed by, predators. The finding that non-consumptive effects of predators are costly to prey and account for over 50% of the effect of predators on plant damage across systems spurred research that documents their importance in agricultural systems. For example, the presence of predatory mites decreased feeding and oviposition by thrips on bean plants, and striped cucumber beetles fly away from cucumber plants when they detect spider predators. However, despite their widespread importance, non-consumptive effects are still rarely explicitly exploited in agriculture, especially against insect pests, largely because we usually lack a cost-effective means of manipulating the pest's responses to their predators. Our discovery that the release of synthetic aggregation pheromone from a stink bug predator of the Colorado potato beetle reduces beetle abundance and plant damage and increases potato yield, gives us the opportunity to develop predator pheromones as a new approach for pest management.The scarecrow is an old example of how to exploit the non-consumptive effect of predators without deploying a live predator, namely using a visual cue to elicit a prey defensive response to protect an agricultural crop. A modern application of this is a precision robotic laser that uses advanced technology in laser diodes and microprocessors to reduce bird damage to sweet corn by 30%. Insects rely heavily on chemical cues to detect their predators and so, we need a chemical scarecrow to elicit their defensive responses.This proposal seeks to develop our ability to use novel predator-based semiochemical strategies by understanding how these chemicals work alone and in combination with a key pest's aggregation pheromone in a sustainable IPM program. There are several general principles that need to be optimized for predator cues to be a useful management tool. 1) Discovering and synthesizing chemical cues that elicit the behavioral responses in the pest; this has been completed in this system. So now we can work on the next steps which are: 2) Understanding the pheromone's relationship with the plant and other members of the community, including other herbivores, conspecifics and natural enemies of herbivores. 3) Understanding the mechanisms of the non-consumptive effect to determine their spatial patterns. 4) Integration of multiple sources of information for the pest, in this case pheromones from the predator and pest itself. Colorado potato beetle (Leptinotarsa decemlineata, CPB) feeding on potato is an ideal system to attempt behaviorally-mediated management using multiple chemical cues because of our existing knowledge of the systems biology and chemistry and because potato is a very important crop and CPB is its key insect pest in large parts of the northern hemisphere.Our prior USDA funded research, completed in 2022, demonstrated that the non-consumptive effect of the native predator Podisus maculiventris (Say), known as the spined soldier bug, reduced the abundance of Colorado potato beetle eggs, larvae and damage to the potato plants. In this work, we isolated the non-consumptive effect of the spined soldier bugs by surgically shortening their mouthparts so they could hunt but not kill their prey. In our search for a more practical way to elicit the non-consumptive effects, our more recent work shows that releasing the spined soldier bug's synthetic aggregation pheromone, elicits the Colorado potato beetle responses to live predators and also reduces beetle abundance and damage. Preliminary results in small field plots shows that deploying the predator pheromone increases potato tuber yield by 10%. In addition, work with the recently available Colorado potato beetle male-produced aggregation pheromone shows strong attraction of both male and female beetles. This proposal seeks to build on this work to develop a strategy integrating these attractive and deterrent semiochemicals. We propose to understand the mechanisms and spatial patterns of the effect of the spined soldier bug pheromone on the community of pest and beneficial insects in potato, and to test the predator pheromone in combination with the attractive Colorado potato beetle pheromone to manipulate beetle movement to concentrate them in the field margins for effective control.
Project Methods
Obj 1a: Effect of predator pheromone on plant resistance to Colorado potato beetle, plant growth and resistance traits. Building on our preliminary results with beetle larvae, we will test whether exposure to the predator pheromone increases individual plant resistance to beetle larvae and adults, measure plant traits involved in resistance, and test whether plant growth is affected by exposure to the pheromone.Objective 1b: We will measure the effects of synthetic predator pheromone on the community of pest and beneficial insects. In both New York and Maryland, we will establish open field plots where we will measure the effect of predator pheromone on the abundance of economically important herbivores: CPB, leafhoppers (Empoasca fabae), aphids (potato aphid, green peach aphid), and natural enemies including spined soldier bug Podisus maculiventris, Perillus bioculatus, Lebia grandis, and lady beetles (including Coleomegilla maculata). By conducting this experiment using the same methods in New York and Maryland, we will take advantage of regional differences in the community of insects on potato plants and also likely conduct our experiments over a greater range of CPB densities. In Maryland, the predator community typically includes a higher abundance of other generalist predators such as Nabis and Geocoris.Objective 1c: Test whether the synthetic predator pheromone alters the impact of live predators on CPB by adding spined soldier bug predators and beetles to large field cages with and without the pheromone treatment. While Obj 1b will inform us of differences in stink bug predator abundance when the predator pheromone is released, in Obj 2c we will test if the predator pheromone changes the impact of spined soldier bugs on Colorado potato beetle oviposition, larval survival and leaf damage. Cages assigned to the pheromone treatment will have a pheromone dispenser containing undiluted pheromone deployed in the central plant as in Obj 1b; control cages will receive an empty dispenser. Each cage will be stocked with 60 first instar CPB larvae. All of the cages will receive one live male and female adult spined soldier bug. We will count the number of larvae surviving daily for 6 days and plant damage at the end of the assay.Obj 2a: Using field releases along a gradient of distances from plants, we will measure the net effect of each pheromone independently on CPB abundance and damage at different spatial scales.We will place pheromone dispensers containing the pure mixture of predator pheromone or empty controls in the center of open plots that are 3 rows wide and 3 meters long. The spatial orientation of the plots will be varied to control for wind or other directional effects. We will count the number of beetles on neighboring plants that are at different distances along the row and across the rows. Plants will be assayed across the row and along the row at 0.3, 0.6, 1 and 2 meters from the dispenser. We will count the number of adult beetles, eggs (and larvae if present) on each plant after 3 days, 1 week, and 2 weeks. If the beetle population is low in the field, we will release adult beetles uniformly outside of the plots. We will also measure the effect of distance on resistance to beetle larvae by excising a newly expanded, undamaged leaflet from the 4th leaf of each of the neighboring plants. These lab larval bioassays will be conducted as described in Obj 1a.What is the spatial scale of the CPB pheromone attraction to adult CPB? We will conduct a mark-recapture study to measure the distance adult beetles are attracted to the beetle aggregation pheromone (Williams 1988) on the USDA farm in Maryland. Beetles will be reared in low density conditions and marked in the lab for use in experiments in early summer, the time when CPB adults emerge from overwintering to find their host plants and when the aggregation pheromone is most attractive. We will conduct these experiments in an open field away from sources of CPB to minimize colonization by beetles that we did not release.Objective 2b: The mechanisms of how the predator and beetle pheromones (independently) impact CPB.We will test the relative importance of the direct and indirect pathways of predator pheromone on Colorado potato beetle. This experiment will inform whether we need to take plant resistance into account when using the predator pheromone. Field experiments at Freeville Farm, NY will be conducted to determine the direct and indirect pathways that can drive effects on beetle performance. Field plots of potato plants will be established with pheromone dispensers in the center of plots. The size of the plot will be based on results from Obj 2a, likely consisting of 1-2 rows of potato plants 2 meters long. There will be a 3-meter buffer between plots. We will assay beetle performance (adult oviposition and larval feeding) on plants in three treatments. Treatment 1 will be plants that are exposed to the undiluted predator pheromone in dispensers before the beetles are in the field (this pre-exposure represents the indirect pathway only). This gives the plant a chance to be induced (respond) without exposing the beetles to the pheromone. Treatment 2 will be plants that are pre-exposed to predator pheromone as in Treatment1, but the exposure will continue after beetles are introduced so that both the plant and the beetles are exposed to the predator pheromone, representing both direct and indirect pathways. Treatment 3 will be a control, with empty dispensers. In treatment 1, plants will be pre-exposed to the predator pheromone for 3 days.Objective 3a: How does the predator pheromone change the attractiveness and response to the beetle pheromone?We will conduct paired choice experiments to see how the presence of predator pheromone affects the preference and response to beetle pheromone by placing pairs of small sets of potato plants in the field and measuring beetle behavior when exposed to one or both of the pheromones. Each plot will consist of two sets of 4 plants spaced apart, the distance between the sets of plants will be based on the spatial information obtained in Obj 2a. The plants will be uncaged in the open field in a location without recent potatoes or CPB. The four treatments will be: 1) plots with beetle pheromone on one side and control on the other, 2) plots with predator pheromone on one side and control on the other, 3) plots with beetle pheromone on one side and predator pheromone on the other, 4) plots with both pheromones on the same side, and 5) control plots with empty dispensers on both sides.Objective 3b. We will deploy the predator and CPB pheromone in the field to manage Colorado potato beetles.This experiment will test the effect of the predator and beetle pheromone on beetle abundance and potato yield in field plots with naturally colonizing beetles over the course of the season. We will conduct this experiment in parallel at our field sites in Freeville, New York and Beltsville, Maryland. Both of these sites have high numbers of naturally occurring CPB due to their history of potato production and so will supply a source of colonizing beetles for the experiments. We will establish four treatments: predator pheromone, beetle pheromone, both pheromones, and a no-pheromone control.