The effects of host-plant genotype on herbivore population dynamics

To determine whether plant genotype can affect long-term herbivore populati on dynamics, we used a density manipulation experiment to compare the dynam ics 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, yieldi ng 80 experimental beetle populations. Populations were initiated by releas ing adult beetles into 2.25 m(2) cages filled with soybeans and located in a small soybean field. Beetle populations were censused weekly for one gene ration. Recruitment curves for beetle populations on each soybean genotype were plotted by fitting a Picker model to the data using likelihood methods . The recruitment curves for all genotypes were significantly different fro m the curves for all other genotypes. The equilibrium beetle density predic ted from the curves varied among genotypes by nearly twofold, and the predi cted dynamics were fluctuating for all genotypes, with the period of fluctu ations differing among genotypes. Performance of beetles also differed amon g genotypes, suggesting that these genotypes vary in some aspect of their q uality as hosts for the beetles. These results indicate that differences in quality among genotypes have the potential to affect long-term herbivore d ynamics.