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.
Feeding, which only occurs in the larval stage for swede midge, 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? Due to begin summer 2019
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
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 summer 2020
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? Due to begin summer 2019
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? Due to begin Fall 2019
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.
Outreach Activities and Participation Summary
In Progress: 37th annual NOFA Vermont Winter Conference, February 16th-18th, 2019 in Burlington, VT. Dr. Yolanda Chen will give a presentation on swede midges, ecologically based pest management for the pest, and pheromone mating disruption.
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).
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/