Marshall W. Johnson Ph.D.

Ph. D., University of California, Riverside, 1979

Research Statement
My research experiences include over 30 years of work on various crop systems (e.g., field crops, vegetables, and tropical crops) and including many important pest species (Liriomyza leafminers, Mediterranean fruit fly, diamondback moth, corn earworm, Dysmicoccus mealybugs, greenhouse and silverleaf whiteflies, etc.) and their natural enemies. Prior to moving to California in 2002, I worked on pineapple pest problems where the interaction between feeding of pineapple mealybugs (Dysmicoccus spp.) and closteroviruses in pineapple plants produce the disease known as ‘pineapple mealybug wilt.’ Ants aggravate this situation because they protect the mealybugs from their introduced natural enemies. Several factors (e.g., Food Quality Protection Act) threaten to reduce the chemical arsenal that farmers use to control the ants and mealybugs. My work in pineapple focused on three areas: development of natural enemy augmentation methods; understanding the role that weeds in the pineapple agroecosystem play as a source of mealybug infestation; and the development of simple, grower-usable sampling techniques for mealybugs. My efforts in Hawaii resulted in the development of techniques to mass-rear thousands of individuals of Dysmicoccus brevipes and its parasitoid Anagyrus ananatis from individual squash fruit; the discovery that Dysmicoccus mealybugs are only found on a few grassy species commonly found adjacent to pineapple plantings, thereby opening the door to disrupting mealybug population dynamics via weed management; and the development of a double-sticky tape sampling method for monitoring mealybug crawlers that can provide information useful for estimating the numbers of mealybugs per pineapple plant.

My research interests are primarily in developing alternative arthropod pest management strategies that minimize pesticide use, but provide growers with practical and feasible controls. My work spans the continuum from basic to applied research. Much of my prior work has focused on the development of IPM programs in vegetable crops, using biological control as the core management tool. As part of this effort to conserve natural enemies, I have conducted studies in the areas of natural enemy biology and ecology, sampling methodologies, arthropod impact on plant physiology and yield, and understanding pesticide resistance in conventional pesticides as well as microbial-based biotic pesticides. My fundamental research interests are in the ecology and behavior of parasitoids, especially mechanisms that they use to locate and parasitize their hosts over a wide array of host plant species, and the competitive interactions of parasitoid species within natural enemy guilds.

I am also interested in why human efforts to manage pests occasionally fail although the necessary science and technology for success exist. This interest evolved from my experiences working with growers in crop systems where pesticides were no longer effective, but alternative controls were available but unused for some reason. I have proposed that human failures to ‘learn, anticipate, and adapt’ often contribute to pest management debacles. Additionally, these failures are not always the fault of growers, but may have their roots at the research or extension outreach levels. This area of investigation could potentially provide insights to enhancing grower education on pest management and strengthening research and extension programs.

My current extension and research activities target insect and mite problems on grapes, stone fruit, almonds and walnuts. Currently, I am developing my extension and research goals for the coming decade. Glassy-winged sharpshooter will most likely receive a significant amount of attention over the next few years. I look forward to meeting growers and pest control advisers throughout California and interacting with them to solve the numerous pest challenges continually faced in the state.