Mortality dynamics of a polyphagous invasive herbivore reveal clues in its agroecosystem success

Authors: Naranjo, Steven; CANAS, LUIS - The Ohio State University; ELLSWORTH, PETER - University Of Arizona

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/26/2022
Publication Date: 5/29/2022
Citation: Naranjo, S.E., Canas, L., Ellsworth, P.C. 2022. Mortality dynamics of a polyphagous invasive herbivore reveal clues in its agroecosystem success. Pest Management Science. 78(10):3988-4055. https://doi.org/10.1002/ps.7018.
DOI: https://doi.org/10.1002/ps.7018

Interpretive Summary: The whitefly Bemisia argentifolii (= B. tabaci MEAM1) is a key pest of multiple field, vegetable and ornamental crops on a global scale. Because the insect can feed on and impact so many plants species and reproduces year-round, it represents a huge challenge for effective pest management. This study was designed to understand the mechanisms governing population development of this insect pest within the broad agricultural landscape. We established representative “ecosystems” in three geographically and climatically distinct areas in Arizona. These systems consisted of a mosaic of six representative hosts (winter broccoli, spring and fall cantaloupes, summer cotton, perennial alfalfa, annual/perennial weeds, and the perennial ornamental lantana). We then used established techniques to directly measure sources and rates of natural mortality of the insect on each host plant and to estimate crop-specific abundances over the year. The quantitative contribution of each cause of mortality varied among hosts and time of the year, but was relatively consistent among geographic sites. Predation (sucking insects), and dislodgement from the plant surface (chewing predation and weather) were consistently the largest sources of mortality. Host plant loss was a large mortality source during cooler months. Predation, dislodgement and host plant loss were determined to be the key factors associated with changes in generational mortality. Survivorship patterns varied among most host plants but mean generational mortality was > 91% except on spring-planted cantaloupe where mean mortality was ~70%. General population trends showed very low densities during winter, low to moderate densities in early spring and late fall and peak populations in mid to late summer. High survivorship on spring cantaloupe is thought to act as a biotic release leading to expansion of pest populations during summer months. These studies have helped to identify vulnerabilities in the insect’s population cycle that can be exploited for improved pest management in all affected crops at a landscape scale. This work will directly benefit growers and pest management professionals and provide a framework for other scientists to explore the landscape dynamics of other multi-crop pests.

Technical Abstract: BACKGROUND: The population dynamics of polyphagous pests such as Bemisia argentifolii (B. tabaci MEAM1) are governed by complex, interacting factors involving its cultivated and wild host plants, seasonality, movement and demography. To understand mechanisms contributing to population development and pest success within the agroecosystem, contiguous multi-host field sites were established in three environmentally distinct areas in Arizona. Life tables quantified and partition models described mortality sources and rates for immature insect stages on each host plant. RESULTS: Predation and dislodgement were the largest sources of marginal mortality, supplied the highest irreplaceable mortality and predation was the key factor. Rates of mortality were best predicted, in order, by source, temperature, host plant, and season. Marginal mortality was highest for 4th stage nymphs followed by eggs. Mortality rates were predicted in descending order by stage, temperatures and season. Survivorship patterns varied among host plants, and generational mortality averaged 70% on spring cantaloupes but nearly 95% on all other hosts. Population density varied seasonally, persisting at low levels on winter hosts and expanding beginning in the spring; perennial hosts and weeds bridge populations year-round. CONCLUSION: Survival on winter hosts such as broccoli, albeit low, enables population continuity while unusually high survivorship on spring crops like cantaloupe is an ecological release propelling population growth and driving regional dynamics in the summer and fall. This detailed understanding of mortality dynamics provides clues to the success of this invasive pest in our agroecosystems and facilitates opportunities for improved pest management at a broader landscape scale.