- Pest Management: chemical control, traps
Swede midge, Contarinia nasturtii Kieffer (Diptera: Cecidomyiidae), is an invasive fly that is threatening the production of organic Brassica crops. The salivary fluids secreted by swede midge larvae severely damage plant tissue and result in scarring and distorted unmarketable produce. Since larvae feed in the protective layers of leaves at the growing tips of plants, traditional IPM tactics are ineffective. The lack of effective management strategies for swede midge has forced some organic growers to abandon Brassica production in the Northeastern US. While synthetic sex pheromones can be used to attract and trap male swede midge, pheromone mating disruption has rarely been implemented in annual rotational systems. It is particularly difficult because mated females can migrate and infest new fields undetected. If attractants are found for female swede midge, then we will be able to detect and directly trap them. Plant odors such as plant volatile organic compounds can attract specialized female insects such as the swede midge. Furthermore, we have found that mated females are particularly attracted to Brassica plant odors compared to male and unmated female swede midge. Plant essential oils can capture plant volatile organic compounds for utilization in lures and traps. In this study, we test Brassica plant essential oils and Brassica plant essential oil blends for attractiveness among mated female swede midge. In addition to quantifying attractiveness among plant odors, we assess the potential for mass trapping and field monitoring applications by measuring essential oil attractiveness among live Brassica host plants and non-host plants.
Project objectives from proposal:
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.