During my doctoral work, I investigated the integrated pest management of the asparagus miner (Ophiomyia simplex (Loew), Diptera: Agromyzidae). The asparagus miner is a putative vector for pathogenic species of Fusarium fungi (see Figure 1), which are the causative agents for “early decline syndrome” in asparagus fields. Fusarium can decrease the life span of an asparagus field by 5-8 years. Newly planted asparagus fields are especially vulnerable to asparagus miner attack, and the immature stages remain invulnerable to insecticide sprays because of its mining habit. While there has been much research looking into controlling the fungi, very little has been devoted to the asparagus miner.
My research looked at various ways to effectively monitor and control asparagus miner populations as part of an integrated pest management program. There were three main pillars to this research. In the first, I developed a degree-day model to accurately predict important phenological events in the life cycle of the asparagus miner (see Figure 2). This involved elucidating the lower developmental threshold for the asparagus miner, and incorporating it into a model that can help guide grower’s decisions about when to time application of pesticide. Once created, the model allows growers to access real-time weather conditions using the Enviro-Weather network in the state of Michigan (see Figure 3) to determine if populations are at a vulnerable point so that the fewest insecticides can be used with the greatest efficacy. In the end, this model will hopefully save growers money and time by reducing the overall number of pesticide applications, as well as spare the nontarget ecological costs associated with insecticide usage.
In the second pillar, I identified naturally occurring arthropod parasitoid species of the miner, as well as examined their abundance over time. I found a total of 12 parasitoid species: seven pteromalids, one braconid, two eupelmids, one bethylid and one eulophid (see Figure 4 for some example specimens). I also examined their life spans when reared on different diets, both artificial and natural, and how this varies relative to the life span of the asparagus miner. I found that sugar-rich resources increase the life spans of both the pest and the natural enemies. In addition, I offered various native and exotic flowers to the asparagus miner and the parasitoid to understand how this affects their life span. I found that Riddell’s goldenrod doubled the lifespan of the asparagus miner, while buckwheat and fava bean were unfavorable food resources for the pest. I ultimately hope that one or two species of flowers can be chosen that can be incorporated in an asparagus field to increase the abundance, life span and efficacy of parasitoids using conservation biological control. The ultimate aim is a system that will be able to suppress asparagus miner populations with few external inputs.
Lastly, I explored the chemical ecology of the asparagus miner/asparagus system. Specifically, I was interested in host plant finding by the asparagus miner, and parasitoid detection of the asparagus miner. To address these topics and related ones, I utilized gas chromatography coupled with mass spectrometry (GC-MS) in the hopes of elucidating the bioactive compounds involved in host-plant location. I performed surveys of asparagus headspace in the lab using greenhouse-reared plants, and have identified many compounds emitted from the plant based on health status (e.g. healthy, herbivore-damaged, or mechanically-damaged). From this survey, I incorporated several compounds present in high abundance in headspace in field baiting experiments to screen the compounds (singly and in combination) for a potential attractant or repellent for the asparagus miner. Ultimately, the goal of this part of my project was to find compounds for use in monitoring and management of the asparagus miner.