MORTALITY DYNAMICS AND POPULATION REGULATION IN BEMISIA TABACI

Authors: Naranjo, Steven; ELLSWORTH, PETER - U OF AZ MARICOPA

Submitted to: Entomologia Experimentalis et Applicata
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/31/2004
Publication Date: 6/1/2005
Citation: Naranjo, S.E., Ellsworth, P.C. 2005. Mortality dynamics and population regulation in bemisia tabaci. Entomologia Experimentalis et Applicata 116: 93-108.

Interpretive Summary: Natural mortality is an important determinant of the population dynamics of a species and an understanding of mortality forces should aid development of better management strategies for pest insects such as sweetpotato whitefly. Cohort-based life tables were constructed for sweetpotato whitefly over 14 generations on cotton from 1997-1999. Rates of predation, primarily by sucking predators, and dislodgement were consistently the largest sources of mortality, although unknown causes and egg inviability were high during some generations. Parasitism was low in all years. Most mortality occurred during the egg stage, and especially the 4th nymphal stage. The median rate of immature survival over 14 generations was 6.6%. Predation during the 4th nymphal stage was identified as the key factor determining changes in generational survival, however, one of the mortality factors appeared to act in a density-dependent manner suggesting that other forces ultimately regulate populations of this insect within cotton fields. A simulation model based on life table results and measured population density suggests that immigration and emigration play important roles in shaping the population dynamics of this pest in the cotton system. Future pest management research should focus on adding additional mortality during the 4th nymphal stadium with special emphasis on conservation programs focused on the predator complex.

Technical Abstract: Cohort-based life tables were constructed for subimaginal stages of Bemisia tabaci over 14 generations on cotton from 1997-1999. Median marginal rates of predation, (0.53), and dislodgement (0.45) were the largest sources of mortality, although unknown causes (0.37) and egg inviability (0.11) were high during some generations. Median mortality by aphelinid parasitoids was low in all years (0.10). Most mortality occurred during the egg stage, and especially the 4th nymphal stadium. The median rate of immature survival over 14 generations was 6.6%. Predation during the 4th nymphal stadium was the primary key factor followed by dislodgement of 4th instar nymphs and egg inviability. There was little evidence of density-dependence for any mortality factor. Irreplaceable mortality was highest for predation and dislodgement. Wind, rainfall, predator densities were associated with dislodgement and rates of predation were correlated with densities of Geocoris spp., Orius tristicolor, Chrysoperla carnea and Lygus hesperus. Simulations suggest immigration and emigration play an important role at or near the onset of economic threshold level populations and towards the end of the cotton-growing season, respectively, and explain departures from observed population patterns based solely on endogenous reproduction and mortality. Future pest management research should focus on adding additional mortality during the 4th nymphal stadium with special emphasis on conservation programs focused on the predator complex.