We will develop recommendations on where and how pheromone dispensers should be deployed for a swede midge PMD program within annual cropping systems. If half of the population mates in the previous year’s field and half in the current year’s field, then double the area would need to be treated. The required area for treatment would be substantially reduced if all adult emerge within the year following pupation. Similarly, a greater understanding is needed to understand how PMD works mechanistically to identify options for manipulating pheromone deployment and dosages.
Swede Midge, Contarinia nasturtii Kieffer (Diptera: Cecidomyiidae) is a relatively new invasive pest of brassica plants such as broccoli, cabbage, kale, canola, etc. The pest was first identified in Ontario in the early 2000s and has since spread across southeastern Canada and northeastern United States of America. Although this pest is small in size (approx. 2 mm when mature), strikingly high rates of damage have been reported, including some reports of up to 100% losses from growers in New York and Vermont.
Swede midge larvae causes multiple damage symptoms (such as scarring, twisted leaves, multiple heads, or complete loss of head), all of which results in unmarketable produce for growers. Feeding occurs within the developing leaves at the growing tip and signs of damage are only apparent after the larvae have already left the plant. These unique characteristics make it extremely challenging to manage swede midge with standard protocols. One promising novel approach is pheromone mating disruption (PMD).
Pheromone mating disruption aims to prevent adult mating by releasing high doses of synthetic female pheromones that confuse males and prevent them from locating copulatory partners. We have previously found that PMD can effectively confuse male swede midge in the field; however, synthesis of the pheromones is costly and can be a significant barrier to grower adoption. Here, we have an opportunity to better understand where swede midge is mating, how to maximize the efficiency of PMD technologies in annual rotation systems, a determine economic and commercial viability of PMD for the management of swede midge.
Determine when and where swede midge adults mate
1.1 Does the distribution of adult midge emergence differ among replicated field plots?
1.2 How does adult dispersal influence their propensity to mate?
1.3 Do we see evidence of sex-biased dispersal based upon distance from emergence sites?
Determine if swede midge mating disruption acts competitively or non-competitively
2.1 What is the relationship between emitter density and male trap capture?
2.2 How does male exposure to high pheromone doses influence their responsiveness to mating with females?
Obj. 1. Determine when and where swede midge adults mate
1.1 Does the distribution of adult midge emergence differ among replicated field plots? Data collection began in July 2019, the study is in progress until the summer of 2022. One set of replicate plots has been successfully maintained through COVID-19 pandemic. Additional trials for building a body of evidence (currently being developed) are due to begin July 2021.
a. Treatments – Mature lab-reared swede midge larvae will be introduced into replicate plots in both early and late summer. Emergence will be monitored for 3 years.
b. Methods – Swede midge colony will be reared using existing protocols. Mature larvae (approx. 500 per plot) will be rinsed into potting soil for pupation. Soil filled pupae will be introduced to five established replicate plots (1 meter squared) at the University of Guelph Elora Research Station in Ontario, in fields free of brassica production for the previous five years. Emergence traps will cover the plots.
c. Data collection – Emerging adult midges will be captured using sticky cards and will be counted and sexed on a weekly basis from April until November over three years. A generalized linear model will be used with a general estimating equation extension (R Studio) to test whether early or late field introduction influences the number of midges found in the emergence traps over time.
1.2 How does adult dispersal influence their propensity to mate? In Progress, estimated completion of data collection is April 2021
a. Treatments- We will test the treatments (N = 100): 1) adult males flown in a wind tunnel prior to mating and 2) adult males held in a vial for the equivalent amount of time.
b. Methods- Male and female midges will be collected upon emergence the morning of trials. Males will be either 1) held in a vial or 2) allowed to fly in a Plexiglas wind tunnel (1 m x 0.5 m x 0.5 m) for 10 minutes. Afterward, males will be put into small deli containers with a single female.
c. Data collection- The frequency of mating will be recorded for a two hour period following treatment. A log-linear model (R Studio) will be used to test if pre-mating dispersal influences the likelihood of adult male mating.
1.3 Do we see evidence of sex-biased dispersal based upon distance from emergence sites? Due to begin June 2021
Treatments, materials, methods, and data collection strategies are currently being developed.
Obj. 2. How does the density of pheromone emitters influence mating disruption?
2.1 What is the relationship between emitter density and male trap capture? Data collection completed September 2019 – Data analysis and methods review have to lead to additional laboratory trials (currently being developed). Due to begin March 2021.
a. Treatments (N = 5) –plots with a 1) high (20 dispenser sites), 2) medium (10 dispenser sites), and 3) low density (1 dispenser site) of pheromone emitters.
b. Methods – We will set up (1.5 m x 1.5 m x 1.5 m) field cages (PVC covered by fine organza) at the University of Guelph’s Elora Research Station. We will test pheromone emitter densities at 1, 10, and 20 emitters per cage, where the total amount of pheromone released in each cage will remain constant. Newly-emerged males and females will be collected from the colony and released into the filed cages on the same day.
c. Data collection- We will place 10 broccoli plants in each cage. We will count the number of larvae found on plants 7 – 10 days after releasing adults. We will test if the total number of larvae per cage differs by treatment using a generalized linear model with a poisson error distribution in R.
2.2 How does male exposure to high pheromone doses influence their responsiveness to mating with females? In progress, estimated completion of data collection is April 2021.
a. Treatments- males exposed (N= 50): 1) 2 ng of the chiral pheromone for 10 min, 2) 2 ng of the chiral pheromone for 10 min, 3) 20 ng for 10 min, and 4) water.
b. Methods – We will expose newly-emerged male midges to the treatments within a glass chamber receiving airflow. We will then place the male and an unmated female together in a small deli container to test whether they mate. Direct observation will be used to determine whether males mated.
c. Data collection – Using a contingency test we will test if the frequency of mating differs among treatments. We will examine whether males mated by: 1) directly observing mating, and 2) whether the females lay eggs.
Education & Outreach Activities and Participation Summary
Presentation: Managing Swede Midge – A New Vegetable Pest, was lead by Dr. Yolanda Chen at the UConn Extension’s 2019 Vegetable & Small Fruit Growers’ Conference held on January 7, 2019. The presentation included an introduction to swede midge, associated damage, report losses from growers, and ecologically based pest management strategies for swede midge (including pheromone mating disruption).
37th annual NOFA Vermont Winter Conference, February 16th-18th, 2019 in Burlington, VT. Dr. Yolanda Chen gave a presentation on swede midges, ecologically based pest management for the pest, and pheromone mating disruption.
Entomological Society of American Annual Conference, November 17th-20th, 2019 in St. Louis, MO. Andrea Swan gave a presentation on how the location of pest mating influences the application of pheromone mating disruption in the management of swede midge.
38th annual NOFA Vermont Winter Conference, February 14th-16th, 2020 in Burlington, VT. Dr. Yolanda Chen will give a presentation on swede midges, challenges to successful management of the pest (in both organic and commercial agricultural settings), ecologically based pest management for the pest, and pheromone mating disruption.
Other Education Activities: What’s Buzzing in Entomology, a VTeens Stem Cafe in association with University of Vermont Extension 4-H. This was a 2-hour long event that included a presentation and hands-on activities for approximately 50 middle and high school youth. The cafe emphasized our work with swede midge, pheromone mating disruption technologies, ecologically based pest management, and IPM. More information can be found at https://teensciencecafe.org/cool-cafes/whats-buzzing-in-entomology/
2019 Natural plant odors may be an effect pest repellent for crops. By Chrissy Sexton. July 23. earth.com news. https://www.earth.com/news/plant-odors-repellent-crops/
2019 Essential oils, a novel way to deal with a major pest. By Fermin Koop. ZME Science. July 24. https://www.zmescience.com/science/essential-oils-pests-24072019/
2019 Garlic could be used to repel insects from crops as scientists find the smell of strange plants acts as a natural pesticide. By Ian Randall. July 24. https://www.dailymail.co.uk/sciencetech/article-7280643/GARLIC-used-repel-insects-crops-experts-plant-odours-natural-pesticides.html#comments
2019 Garlic on broccoli: A smelly approach to repel a major pest. Science Daily. July 23. https://www.sciencedaily.com/releases/2019/07/190723085955.htm
2019 Across the Fence. WCAX News. “Baffling Bug – Research at UVM on the Swede midge”. https://www.youtube.com/watch?v=3JeDbV1_q0k
2019 University of Minnesota Extension Fruit and Vegetable News. Interviewer Natalie Hoidal. “What’s Killing My Kale Episode 27: Swede Midge Management – an overview of what we know”. October 04.