Crop diversity influences arthropod communities and other biotic factors
Open Access
- Author:
- Baniszewski, Julie
- Graduate Program:
- Entomology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 28, 2021
- Committee Members:
- Edwin Rajotte, Major Field Member
John Tooker, Chair & Dissertation Advisor
Gregory Roth, Outside Unit Member
Armen Kemanian, Outside Field Member
Gary Felton, Program Head/Chair - Keywords:
- crop diversity
arthropod community
polyculture
silage
wheat
coffee - Abstract:
- Modern agriculture has pushed for efficiency in its practices, genetics, equipment and new technologies. Unfortunately, achieving higher productivity often relies on greater levels of inputs. Consequently, intensive agricultural systems provide simplified habitats (i.e., crop fields) that are favorable to pests and require chemicals to maintain desired levels of productivity or quality. The side effect of synthetic chemicals, monoculture crops and a drive for the highest yields is reduced biodiversity in agroecosystems. Reduced biodiversity can be problematic because fields with fewer natural enemies are likely to be more vulnerable to pests. An alternative to simplified agricultural production system is to incorporate plant diversity within a cropping system. Although there are several theories explaining the benefits of increasing plant diversity, I focus largely on complementarity. The theory of complementarity is that, by increasing plant species diversity within a system, the planted species would be able to more efficiently utilize available resources, or complement each other. Similarly, the resource concentration hypothesis is relevant because it states that herbivorous arthropods thrive in plant communities that are dense with their host plant species whereas their populations face more challenges when their preferred host plant species are less abundant, as one would find in more diverse cropping systems that support more robust populations of predators and parasitoids. The idea of complementarity is often applied to plant production, whereas the resource concentration hypothesis is largely descriptive of how arthropod populations are influenced by plant diversity. Therefore, I have incorporated both hypotheses in this thesis to predict how several cropping systems may benefit from various types of plant diversity. The first chapter focuses on intraspecies diversity in wheat (Triticum aestivum L.) over three years of field study. I hypothesized that wheat grown in cultivar mixtures would have higher yields, better disease suppression and lower arthropod pests compared to plantings of single varieties. By growing each variety alone and mixing four varieties into one mixture, I was able to compare benefits of disease, arthropod community and yield. Overall, I did not find evidence that the mixture provided a higher yield, but was able to show that cultivar mixtures of wheat help suppress foliar diseases similar to that of chemical fungicides without negatively affecting yield or economic value. In my second chapter, I incorporated plant species diversity within a forage system to test how diversity could benefit an annual forage crop for improving biomass production or increasing economic return by reducing insect and disease pests and having greater stability from year to year compared to growing each species separate. Over a four-year field study, I compared seven treatments of species mixtures and monocultures of maize (Zea mays L.), soybean (Glycine max (L.) Merrill), sorghum (Sorghum bicolor (L.) Moench) and sunflower (Helianthus annus L.) split with and without insecticide and measured the effects of species mixtures on insects, disease, yield and economic value. Although biomass was not increased in mixtures, partial return over variable costs was similar in the four-species mixture compared to maize or sorghum alone. There were low insect pests abundances and disease pressures overall. Finally, I also quantified detrimental effects of insecticides on arthropod communities, including natural enemies. The third chapter also focuses on a similar annual forage system as Chapter 2, including maize (Zea mays L.), soybean (Glycine max (L.) Merrill), sorghum (Sorghum bicolor (L.) Moench) and sunflower (Helianthus annus L.), but addresses questions about weed suppression. Here, my study comprised a greenhouse component and two years of field research to evaluate weed suppression based on functional group of crops and weeds (broadleaves and grasses) as well as potential attraction of weed seed predators, specifically carabid beetles. Interestingly, I found both weed suppression and abundances of weed seed predators to be greatest in monocultures as opposed to a higher level of diversity within crop mixtures, indicating that competition rather than complementarity between crops, may have a larger role in these systems. The fourth chapter focuses on limitations I experienced in the application of interspecific mixtures including maize (Zea mays L.), soybean (Glycine max (L.) Merrill), sorghum (Sorghum bicolor (L.) Moench) and sunflower (Helianthus annus L.) and how I modified and overcame challenges associated with mixtures in field research. My aim with this chapter was to encourage additional research and bridge scientific knowledge and research with the application of incorporating mixtures into large scale agronomic production systems. My final chapter presents research done over a single season within a coffee (Coffea arabica L.) system in Costa Rica. I evaluated the potential of shade tree diversity within coffee plantations to attract a larger diversity of arthropods, including predatory arthropods, to help control effects of a severe coffee pest, coffee berry borer (CBB; (Hypothenemus hampei) (Ferrari) (Coleoptera: Curculionidae, Scolytinae)). Although I was only able to show lower coffee berry borer infestation in May associated with shade trees compared to sun coffee, I also found an interesting correlation with an increase in CBB in proximity to sugarcane fields. I highlight some ways that coffee growers could mitigate immigration of CBB into their fields and reduce future generations of CBB.