Leafhoppers (Hemiptera: Cicadellidae): Presence and Control in Dairy Cropping Systems
Open Access
- Author:
- Bliss, Daniel
- Graduate Program:
- Entomology (MS)
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 19, 2023
- Committee Members:
- Gary Felton, Program Head/Chair
John Tooker, Thesis Advisor/Co-Advisor
Heather D Karsten, Committee Member
Andrew R Deans, Committee Member - Keywords:
- Leafhopper
Dairy Cropping
IPM
Biological Control - Abstract:
- The challenge of modern agriculture is producing sufficient food for a large population while combating the adverse effects of climate change. These effects are likely to be many and varied, including increases in temperature, greater unpredictability of extreme weather, and expanded ranges of agricultural pests. The task of researchers is to find sustainable solutions to these problems while keeping farms economically profitable. This thesis examines the threat posed by specific insect pests to dairy crop production, with the goal of identifying effective and sustainable management solutions for each pest. To do this I have split my thesis into three chapters, each of which examines an aspect of pest management in dairy cropping. In Chapter 1 of my thesis, I review methods of controlling leafhopper populations in dairy cropping systems. Leafhoppers (Hemiptera: Cicadellidae) are major threats to agricultural production around the world. They are diverse, abundant, and capable of reducing crop quality and yield through feeding damage and vectored pathogens. While many studies have investigated the role of leafhoppers on individual crops, few have broadened their view to address the potential effects of leafhoppers on an industry. My review attempts to fill the gap in our understanding by examining the effects of leafhoppers on three of the largest acreage crops in the United States: alfalfa (Medicago sativa), maize (Zea mays), and soybean (Glycine max). Each of these crops contributes to the success of the dairy industry, the products of which have a major impact on the U.S. economy. Throughout the review I analyze leafhopper management strategies in each of these crops to identify which can contribute to successful production. In doing so I hope to shed light on the impact of leafhoppers in an important industry while providing a practical resource for researchers and growers. In Chapter 2, I track populations of a specific type of leafhopper—the potato leafhopper (PLH; Empoasca fabae)—in alfalfa/orchardgrass fields. PLH is a major threat to alfalfa production in the eastern regions of the United States, reducing crop quality and yield through feeding. To combat this pest, growers often rely on insecticides. While effective, these insecticides are expensive and damaging to the environment. Integrated Pest Management (IPM) was developed to reduce reliance upon pesticides in crop production while maintaining a focus on profitability and sustainability. While IPM has become a model for pest control, few studies have investigated its long-term benefits for insect management. Using data from four years of sampling, I studied PLH in alfalfa to compare a preemptive insecticide-based approach (i.e., conventional strategy) to an IPM-based approach (i.e., innovative strategy) in terms of insect control and profitability. My goal was to identify whether an innovative strategy could compete with a conventional strategy in terms of crop quality, crop yield, and insect management. I found that the innovative strategy produced similar quality to the conventional strategy while requiring less than half the number of insecticide applications and a lower per-plot cost. Despite a decreased cost per plot, the innovative strategy hosted a larger population of PLH and produced a lower total annual crop yield (though only in the second year of alfalfa growth). These results prompted me to test the effectiveness of PLH-resistant alfalfa to see whether it is a benefit or hinderance to alfalfa production. I found that PLH-resistant alfalfa reduced potato leafhopper population size by approximately 26% but did not significantly influence alfalfa quality or yield. This study demonstrates the values and costs of IPM in growing alfalfa and provides evidence that an innovative management strategy can be competitive with insecticide-based management programs. Chapter 3, I attempt to find a solution to PLH damage in alfalfa by promoting spider-mediated biological control. Biological control is a foundational aspect of IPM that uses predators and parasitoids to naturally reduce pest populations in agricultural fields. While biological control is effective in many situations, not every crop system has a suitable natural enemy for its suite of pests. As generalist predators, spiders have potential to act as effective biological control agents across a diverse range of crops and pests. Previous research has often neglected spiders, particularly foliage-dwelling spiders, in biological control because their populations tend to be low in agricultural fields. To assess the control potential of spiders, I focused on alfalfa and its most damaging pest in Pennsylvania, PLH. As tall structures tend to intercept ballooning spiders (a common form of travel) and improve their prey capture through superior web-building, I tested the influence of vertical structure on spider populations in an alfalfa/orchardgrass field. I used a factorial design which crossed two factors, bamboo stakes (non-living structure) and sorghum sudangrass (SS; living structure) to produce four treatments: stakes, SS, stakes + SS, and the control (no structure added). I included both living and non-living structures to identify whether structure type influenced spider populations. I sampled spiders using sweep-netting and pitfall traps to capture both foliage-dwelling and ground-dwelling populations. My results showed that vertical structure significantly increased populations of foliage-dwelling spiders. To identify the influence of spiders on pest populations, I used sweep-nets to capture PLH. I caught significantly fewer PLH in plots which contained both types of vertical structure. When comparing spider and PLH numbers, my results revealed a trend toward more effective PLH control by living structure, but no statistically significant difference.