Effects of Beetle Density and Time of Day on the Dispersal of <I>Gratiana boliviana</I> (Coleoptera: Chrysomelidae)
AbstractThe leaf beetle, Gratiana boliviana Spaeth, is a biological control agent of tropical soda apple (Solanum viarum Dunal), a noxious weed invading the rangeland and agricultural fields of Florida and other southeastern states. In caged experiments, we examined the influence of beetle density and the time of day on the dispersal of the leaf beetle. Increasing beetle density from 2 to 100 beetles per plant did not increase G. boliviana dispersal, as long as the host plants were not severely defoliated. An increase in beetle density from 10 to 100 beetles per plant significantly reduced the per capita fecundity from 0.3 to 0.02 eggs over a 24-h period. Thus, a mass rearing method for G. boliviana should consider the potential detrimental effect of increasing density on the fecundity of the leaf beetle. When the dispersal activity of the leaf beetle was observed between 8:00 and 18:00 h, the proportion of beetles dispersing from a given plant increased throughout the morning hours and peaked at noon. A monitoring or sampling program of G. boliviana should be conducted in the early morning or late afternoon when the beetles' tendency to disperse is the lowest in order to more accurately sample for the population density in a certain area. Beetle density and the time of day interacted to influence the proportion of G. boliviana dispersing from a given plant. The proportions of beetles that dispersed were not different among the different time periods at densities of less than 40 beetles per plant. At or above 40 beetles per plant, the proportion of beetles that dispersed peaked at noon. This study suggests that a myriad of factors, including density, feeding damage, photoperiod and host plant quality, interact to determine the dispersal pattern of G. boliviana.
View this article in BioOne
Copyright for any article published in Florida Entomologist is held by the author(s) of the article. Florida Entomologist follows terms of the Creative Commons, Attribution Non-Commercial License (cc by-nc). By submitting and publishing articles in Florida Entomologist, authors grant the FOJ and Florida Entomologist's host institutions permission to make the article available through Internet posting and electronic dissemination, and to otherwise archive the information contained both electronically and in a hard printed version. When used, information and images obtained from articles must be referenced and cited appropriately. Articles may be reproduced for personal, educational, or archival purposes, or any non-commercial use. Permission should be sought from the author(s) for multiple, non-commercial reproduction. Written permission from the author(s) is required for any commercial reproduction.