Modeling Biological Control: The Population Regulation of Nezara viridula by the Parasitoid Trichopoda giacomellii)

LILJESTHRÖM, G. AND J. E. RABINOVICH

ECOLOGICAL APPLICATIONS

Año: 2004 vol. 14 p. 254 - 267

1051-0761

The role of the aggregated distribution of attacks, a castration effect (cessation of reproduction of the parasitized hosts) and the differential selectivity for hosts by the parasitoid Trichopoda giacomellii on the population regulation of its host, Nezara viridula, was investigated using a detail-rich simulation model. The model parameters were estimated either in the laboratory or under field conditions. Additionally, key parameter values were estimated by fitting the model to field data of nine generations of the host and the parasite, respectively. The model proved to be robust, with a high coincidence between the parameter values obtained by fitting the model and the field/laboratory estimates. In both cases, the model reproduces the regular oscillations observed in the real system. Stability analysis revealed that the model could have different dynamic behaviors, unstable or stable depending on the parameter values. It was shown that the aggregated distribution of attacks, as described by the negative binomial distribution with a low k value (aggregation parameter of the parasitoid's egg distribution among hosts), was the dominant mechanism associated with the stability of the model, although there was some degree of interaction with the other two mechanisms (the castration effect and the differential selectivity for hosts). However, neither of these two mechanisms was able to regulate the parasite-host populations in the absence of the aggregated distribution of attacks. The field/laboratory estimate of parameters falls in all cases in the stability region with normal population densities, while the best parameter estimates by fitting the model sometimes fell in the region of the parameter space where the parasite became extinct. This is one of the few cases in which the theoretical stability behavior conclusions derived from simple mathematical models could be assessed with a complex and realistic simulation model based on field/laboratory data, and the dominant stabilizing mechanisms determined. Specifically, the best fit and the field estimates of the parameter k, an indicator of the degree of aggregation of the distribution of attacks, coincided in values less than 1, as predicted by theory for stable parasite-host populations. Larger k values lead to instability.