| Cropping systems are faced with a multitude of pest problems and as a result must implement a diverse suite of pest management tactics. In the potato cropping system, the Colorado potato beetle is one of many serious potato pests. Traditionally, insecticides have been the primary control method, but because of the beetle's rapid development of resistance to most chemicals, alternative control measures are being considered. While the use of entomopathogens seems promising for potato beetle control their effectiveness under field conditions has been quite variable. In chapter 2, I examined the impact of mustard green manures, a common practice for plant parasitic nematode control, on entomopathogen infection. I found that the use of mustard green manures negatively impacted entomopathogen infection in both field surveys and laboratory studies. In chapter 3, I focused on the impact of animal manure and synthetic fertilizer on the inundative release of entomopathogenic nematodes (EPNs). I found that host infection by EPNs was negatively impacted by animal manure compared to synthetic fertilizer. Furthermore, these data indicate that increased microbial activity, consisting of EPN competitors and antagonists, in soil amended with animal manure may decrease EPN effectiveness. Finally, in chapter 4, I tested the hypothesis that through conservation biological control, herbivore suppression strengthens with increasing natural enemy biodiversity. Colorado potato beetle eggs and small larvae occur in plant foliage where they are attacked by a guild of generalist predators, whereas later-stage larvae burrow into the soil to pupate and are attacked by a guild of entomopathogens. I found that potato beetle densities decreased, and plant biomass increased, with greater enemy biodiversity. However, beetle suppression strengthened only for predator-pathogen pairs, and not for pairings within the same natural enemy guild. This body of research shows that crop health and pest management strategies may interfere with biological control using EPNs; in addition, it shows that conservation of entomopathogens is important to improving biological control. |
