Progress report for GNE21-271
Project Information
Objective 1: Determine the relative attractiveness of Brassica plant extracts on female swede midge.
1.1 How do mated and unmated female swede midge respond to individual host plant extracts?
We will test whether swede midge females are attracted to individual plant extracts (Red Russian Kale, White Russian Kale, broccoli, cauliflower, collard greens) 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 plant extracts, 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 extracts versus individual host plant extracts?
We will test whether swede midge females differ in their preference for host plant extract blends (Red Russian Kale, White Russian Kale, broccoli, cauliflower, collard greens) compared to individual plant extracts (Red Russian Kale, White Russian Kale, broccoli, cauliflower, collard greens). Extract blends will consist of combinations of the most attractive host-plant extracts determined in objective 1.1. Testing rates of attractiveness through choice testing will identify which single extract or blended extract combinations attract the most females. We will also test for differences in attraction among mated and unmated females to the different host plant extract treatments, replicating the main factors over 50 replicate females.
Objective 2: Test the attractiveness of host plant extracts or extract blends among live plants.
2.1 How do female swede midge respond to host plant extracts or extract 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.
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
Objective 1: Test the attractiveness of steam distillation extracts from host plants on female swede midge.
Objective 1.1 How do mated and unmated female swede midge respond to individual steam distillation extracts from host plants?
Previous trials aimed at establishing host plant preference among male, unmated female, and mated female swede midge resulted in mated female swede midge displaying host plant preference while unmated female and male swede midge did not (unpublished). For this reason, we omitted unmated females from trials and only tested females with unlimited access to mates. We could not guarantee mating success but a random selection of 168 females resulted in 57.74% mated (unpublished) using this method.
To establish swede midge attraction to steam-distilled extracts from 5 Brassica host plant varieties, we will use behavioral assays using a two-choice (y-tube) olfactometer system. The olfactometer pushes clean filtered air into the two arms of a glass y-tube, which controls for background odors and allows insects to distinguish between two odor sources.
Individual swede midge will be placed in the y-tube with a Brassica extraction in one arm and water control in 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 treatment arm will alternate to remove directional bias. The five host plant extracts (Red Russian Kale. White Russian Kale, broccoli, cauliflower, and collard greens) will be tested individually using a minimum of 100 individual female swede midge 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 15 seconds. We will analyze if the females are attracted to the plant extracts using a chi-square goodness of fit test with defined equal probabilities among the three behavioral choices as the null hypothesis. This allows us to account for the behavioral display of No Preference. Trials are complete and statistical analysis is planned for February 2023.
1.2 How do mated and unmated female swede midge respond to combinations of host plant extracts vs individual host plant extracts?
Previous trials aimed at establishing host plant preference among male, unmated female, and mated female swede midge resulted in mated female swede midge displaying host plant preference while unmated female and male swede midge did not (unpublished). For this reason, we omitted unmated females from trials and only tested females with unlimited access to mates. We could not guarantee mating success but a random selection of 168 females resulted in 57.74% mated (unpublished) using this method.
Individual swede midge will be placed in a two-choice (y-tube) olfactometer system with host-plant extract blends in one arm and single host-plant extract in the other arm. The treatment arms will alternate to remove directional bias. Treatments will include host plant extract blends determined based on a hierarchy of attraction determined in Objective 1.1. The attractiveness of host plant extract blends will be tested against individual host plant extracts of the most attractive pairings. We will replicate the treatment over 60 mated females. We will analyze female behavior to establish a preference for host plant extract blends or single host plant extracts using a chi-square goodness of fit test with defined equal probabilities among the three behavioral choices as the null hypothesis. This allows us to account for the behavioral display of No Preference. Trials are complete and statistical analysis is planned for February 2023.
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 host plant extract 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.
Education & Outreach Activities and Participation Summary
Participation Summary:
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.