Methodology for developing life tables for sessile insects in the field using the Whitefly, Bemisia tabaci, in cotton as a model system

Authors: Naranjo, Steven; ELLSWORTH, PETER - University Of Arizona

Submitted to: Journal of Visualized Experiments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/2017
Publication Date: 11/1/2017
Citation: Naranjo, S.E., Ellsworth, P. 2017. Methodology for developing life tables for sessile insects in the field using the Whitefly, Bemisia tabaci, in cotton as a model system. Journal of Visualized Experiments. 129:e56150. doi:10.3791/56150.
DOI: https://doi.org/10.3791/56150

Interpretive Summary: An understanding of the population dynamics of a pest insect is a critical foundation to the development of more ecological and sustainable pest management systems. Field-based life tables are a robust method to gain this knowledge. Life tables allow the quantification of rates of mortality in pest populations and also permit the identification of important mortality sources (predation, parasitism, insecticides, etc.). Developing life tables for insects with multiple generations per season is particularly challenging because there is no clear delineation of the start of any one generation. The work here provides a detailed description of a method that allows accurate life tables to be constructed for an insect with multiple overlapping generations each year. These methods take advantage of the sessile nature of the immature stages of particular insects and is exemplified with a key pest of cotton in the western US, the sweetpotato whitefly, Bemisia tabaci. The method is based on locating and marking the location of individual insects in the field that can then be observed repeatedly over time to measure development from one stage to the next and to identify stage-specific causes of death associated with natural and introduced mortality forces. Analyses explain how to correctly measure multiple mortality forces that act contemporaneously within each stage and how to use such data to provide meaningful population dynamic metrics. An example of the method and analyses is presented for a study that examined the impact of bottom-up (plant quality) and top-down (natural enemies) effects on the mortality dynamics of whitefly in the cotton system. The method is robust and applicable to a number of other insect and plant systems and will be of value to other scientists interested in insect population dynamics and management.

Technical Abstract: Life tables provide a means of measuring the schedules of birth and death from populations over time. They also can be used to quantify the sources and rates of mortality in populations, which has a variety of applications in ecology, including agricultural ecosystems. Horizontal, or cohort-based, life tables provide for the most direct and accurate method of quantifying vital population rates because they follow a group of individuals in a population from birth to death. Here protocols are presented for conducting and analyzing partial cohort-based life tables in the field that takes advantage of the sessile nature of the immature life stages of a global insect pest, Bemisia tabaci. Individual insects are located on the underside of cotton leaves and are marked by drawing a small circle around the insect with a non-toxic pen. This insect can then be observed repeatedly over time with the aid of hand lenses to measure development from one stage to the next and to identify stage-specific causes of death associated with natural and introduced mortality forces. Analyses explain how to correctly measure multiple mortality forces that act contemporaneously within each stage and how to use such data to provide meaningful population dynamic metrics. The method does not directly account for adult survival and reproduction, which limits inference to dynamics of immature stages. An example is presented that focused on measuring the impact of bottom-up (plant quality) and top-down (natural enemies) effects on the mortality dynamics of B. tabaci in the cotton system.