Developing a plant-based attractant to trap swede midge, Contarinia nasturtii (Diptera: Cecidomyiidae)

Progress report for GNE21-271

Project Type: Graduate Student
Funds awarded in 2021: $14,438.00
Projected End Date: 02/01/2023
Grant Recipient: The University of Vermont
Region: Northeast
State: Vermont
Graduate Student:
Faculty Advisor:
Dr. Yolanda Chen
University of Vermont
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Project Information

Project Objectives:

Objective 1: Determine the relative attractiveness of Brassica plant essential oils on female swede midge.

1.1 How do mated and unmated female swede midge respond to individual host plant essential oils? 

We will test whether swede midge females are attracted to individual essential oils (broccoli, cauliflower, kale, canola, and cabbage) using a two-choice, y-tube olfactometer system for choice testing. Using paired choice tests along with a water control, we will generate a hierarchy of female preferences for the essential oils, which will help us determine the most attractive ones. Additionally, we will test for differences in attraction among mated and unmated females as they could respond differently to host plant essential oils. We will repeat the test on over 50 female midges to develop a more population-level understanding of female preference.

1.2 How do mated and unmated female swede midge respond to combinations of host plant essential oils versus individual host plant essential oils?  

We will test whether swede midge females differ in their preference for essential oil blends (combinations of broccoli, cauliflower, kale, canola, and cabbage) compared to individual essential oils (broccoli, cauliflower, kale, canola, or cabbage). Essential oil blends will consist of combinations of the most attractive host-plant essential oils determined in objective 1.1. Testing rates of attractiveness through choice testing will identify which single essential oil or blended essential oil combinations attract the most females. We will also test for differences in attraction among mated and unmated females to the different essential oil treatments, replicating the main factors over 50 replicate females.

Objective 2:  Test the attractiveness of essential oils or essential oil blends among live plants.

2.1 How do female swede midge respond to host plant essential oil or essential oil blends among live host and non-plants?

We will use the most attractive treatments from Objective 1 in baited Jackson traps to determine their efficacy as lures among Brassica host plants and non-host plants in a laboratory setting. We will use cage trials for greater experimental control on the number of insects released. These trials will give us an accurate measure of what percentage of the released females are trapped to measure the efficacy of an attractant. 

Introduction:

The purpose of this project is to develop a plant-based attractant for swede midge. Swede midge is an invasive insect pest that attacks all major Brassica crops. Swede midge larvae secrete digestive fluids that severely damage plant tissue and cause scarring, multiple shoots, deformed plant growth, and the complete loss of marketable plant parts (Hallet 2007). Feeding by even a single swede midge larva can lead to unmarketable produce (Stratton et al. 2018). Given that only systemic neonicotinoids are effective for crop production, the lack of products for organic management of the midge and heavy losses due to swede midge have forced some organic growers to abandon Brassica production in the Northeast. More recently, swede midge has increased its distribution and is now reported throughout Eastern Canada and North Eastern United States (Chen et al. 2009, Hodgdon unpublished). 

The biology of the midge makes it an extremely challenging pest to manage. Swede midge belongs to the family Cecidomyiidae; a group of flies known for their ability to strongly influence plant growth and plant defenses (Stuart et al. 2012).  Swede midge larvae secrete salivary fluids at or near the growing tips of plants essentially targeting the most economically significant plant parts.  Larvae feeding at the growing tips are shielded from foliar insecticides (Wu et al. 2006, Hallet et al. 2009). In addition, damage symptoms are not apparent until mature larvae have left the plants for the protective cover of the surrounding soil during pupation (Stratton et al. 2018).  Furthermore, adult swede midge are tiny (2 mm) and have a life span of 2-3 days, making them extremely challenging to observe in the field and preventing successful management with traditional scout and spray tactics. Due to the severity of crop damage and the elusive nature of this pest, there is a strong need for innovative pest management techniques. 

One promising solution is the use of pheromone mating disruption (PMD) as a potential management strategy. PMD technology releases high levels of synthetic female sex pheromone to prevent males from finding females and reduces mating. The female swede midge sex pheromone has been identified and can be synthesized commercially (Hillbur et al. 2005). PMD can disrupt males from finding females in the lab and in the field (Hodgdon et al. 2019). However, females can still mate outside of treated areas and migrate into Brassica fields to lay eggs. An attractive lure for mated females can capture individuals that temporally or spatially evade PMD.  Furthermore, combining the two technologies could result in a mass trapping system that has the potential to provide high management success. Mass trapping aims to reduce pest pressure by luring large numbers of the target pest with baited traps. Developing a female attractant and combining male and female attractants has the potential for trapping large numbers of swede midge. A successful mass trapping system for swede midge will reduce severe economic losses and aligning with organic management practices to increase the ability to manage pests in a sustainable agriculture framework.

Research

Materials and methods:

Objective 1: Test the attractiveness of host plant essential oils on female swede midge.

Objective 1.1 How do mated and unmated female swede midge respond to individual host plant essential oils? 

To establish the midge's odor preferences among Brassica varieties, we will use behavioral assays using a two-choice (y-tube) olfactometer system, which is already in our lab. The olfactometer pushes clean filtered air into the two arms of a glass y-tube, which controls for background odors and allows for insects to distinguish between two odor sources. Using the olfactometer effectively allows us to ensure that insects are only exposed to the two essential odors. 

 

Individual swede midge will be placed in the y-tube with a Brassica essential oil in one arm and a control or empty side in on the other arm. The response of each female will be a separate replicate. Females will have five minutes to make a choice, after which they will be removed from the tube. The treatments will be randomly assigned to each arm for each replicate. The five essential oils (broccoli, cauliflower, kale, canola, cabbage) will be tested in a randomized complete block design. The study design will be repeated across mated and unmated females to control for any variation in response among the two groups. We will repeat the trials over 50 midges for each treatment (essential oil and female reproductive status), to develop a more population-level understanding of female preference. We will use insect choice as a proxy for attractiveness. We define insect choice as an individual entering one arm of the y-tube and staying there for more than 30 seconds. We will analyze if the females are attracted to the plant essential oils using binomial exact tests. Essential oils are currently in production for 5 brassica varieties (Red Russian kale, broccoli, canola, cauliflower, and cabbage). Trials are due to begin March 2022

 

1.2 How do mated and unmated female swede midge respond to combinations of host plant essential oils vs individual host plant essential oils?  

Individual swede midge will be placed in a two-choice (y-tube) olfactometer system with host-plant essential oil blends in one arm and single host-plant essential oil in the other arm.  Two choice treatment positions will be randomized for each replicate. Treatments will include three essential oil blends determined based on a hierarchy of attraction determined in Objective 1.1. The attractiveness of essential oil blends will be tested against all three single essential oils (broccoli, cauliflower, and canola), through all possible pairings. We will replicate the treatment over 25 females mated and 25 unmated females for each paired contrast between essential oils. We will analyze if the females respond to the treatments differently by using binomial exact tests. Host-plant essential oil blends will be influenced by results of experiment 1.1.  Experiment 1.2 is due to begin in May 2022

 

Objective 2:  Test the attractiveness of essential oils or essential oil blends among live host plants.

2.1 How do female swede midge respond to host plant essential oils or essential oil blends among live plants? 

We will test the most attractive essential oil treatments from objective one as lures for female swede midge when broccoli host plants or non-host plants are present. Each replicate will consist of a 3ft x 3ft x 3ft cage with a standard Jackson trap baited with the essential oil treatment, along with six eight-week-old organic broccoli plants, tomato plants, Swiss chard, or a fake plant as a control (plants grown in 4" pots amended with compost). We will use broccoli as host plants because they are highly susceptible to midge damage and economically significantly regionally. We will add a known number of female midges from the existing midge colony in the lab. Groups of 50 mated females will be counted prior to introduction so that we can accurately assess the proportion of individuals that were successfully trapped. We will count the number of female midges caught in the traps over 25 replicates. We will also dissect each host plant and count the number of larvae present from each replicate. The most attractive treatments will catch the highest number of females. We will test if the total number of female midges caught in the trap differs among the treatments using a generalized linear regression with a Poisson error model in R latest model.  Due to begin July 2022

Participation Summary

Education & Outreach Activities and Participation Summary

Participation Summary:

Education/outreach description:

Our outreach efforts aim to help growers become familiar with the basic biology and ecology of swede midge. If we develop a female attractant, we can promote an understanding of our proposed strategies’ successful implementation. 

 

  • Infographic 

We will develop a data-rich infographic to explain swede midge ecology and explain how applied chemical ecology approaches like pheromone mating disruption and mass trapping can be implemented in organic vegetable cropping systems. We view this as the most reader-friendly approach to information dissemination. 

 

The infographic will be shared through Twitter through our network of collaborators. It will also be sent via email listservs for extension specialists and to vegetable growers, such as Cornell Cooperative Extension Vegetable Program and Eastern NY Commercial Horticulture Program (~2,000 email subscribers), UVM Extension, Vermont Vegetable and Berry Growers Association (~1,000 email subscribers), Northeast Organic Farming Association (NOFA- VT 10,000, NOFA-NY 3,000 newsletter subscribers) and other grower listservs and social media outlets.

 

  • Outreach presentations 

VT – Northeast Organic Farming Association Winter Conference. Dr. Chen and Ms. Swan will present their results. They will relay the latest results to increase farmer knowledge of swede midge ecology and best practices for swede midge management. 

  • Publications

We will publish peer-reviewed articles on our findings and implications for the successful management of swede midge as well as directions for future research.

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.