THE EFFECTS OF HOST-PLANT GENOTYPE ON HERBIVORE POPULATION DYNAMICS

Abstract

To determine whether plant genotype can affect long-term herbivore population dynamics, we used a density manipulation experiment to compare the dynamics of Mexican bean beetle populations living on four genotypes of soybeans. Five densities of beetle populations were created on each plant genotype. Each combination of density and genotype was replicated four times, yielding 80 experimental beetle populations. Populations were initiated by releasing adult beetles into 2.25 m2 cages filled with soybeans and located in a small soybean field. Beetle populations were censused weekly for one generation. Recruitment curves for beetle populations on each soybean genotype were plotted by fitting a Ricker model to the data using likelihood methods. The recruitment curves for all genotypes were significantly different from the curves for all other genotypes. The equilibrium beetle density predicted from the curves varied among genotypes by nearly twofold, and the predicted dynamics were fluctuating for all genotypes, with the period of fluctuations differing among genotypes. Performance of beetles also differed among genotypes, suggesting that these genotypes vary in some aspect of their quality as hosts for the beetles. These results indicate that differences in quality among genotypes have the potential to affect long-term herbivore dynamics.