Modeling Biological Control: The Population Regulation of Nezara Viridula by Trichopoda Giacomellii

Abstract

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.

Plugging Space into Predator‐Prey Models: An Empirical Approach

“…These models combine small-scale observations or experiments for measuring process rates with field measurements of spatial variability. This approach has a long history in the study of host-parasitoid interactions, where models originally developed by Bailey et al (1962) and May (1978) have been used to examine the dynamic consequences of heterogeneity in the distribution of parasitoid attacks (e.g., Hassell 1980;Jones et al 1993;Liljesthröm and Rabinovich 2004). A similar approach has been used in studies of host-parasite interactions (Dobson and Hudson 1992;Barlow 2000).…”

The functional and numerical responses ofTrissolcus basalis(Hymenoptera: Platygastridae) parasitizingNezara viridula(Hemiptera: Pentatomidae) eggs in the field

“…We assume the latter to be a plausible explanation because the third generation of N. viridula adults (in pre-reproductive stage) leaves the feeding/reproducing area in search for hibernating shelters (in our study area the hibernation period lasts approximately 5 months of the colder period of the year). N. viridula individuals leaving hibernation re-colonize the area in the following spring and reproduce, originating the first new generation of eggs (Liljesthröm & Bernstein, 1990; Liljesthröm & Rabinovich, 2004). T. basalis also hibernates in the adult stage, and Doetzer & Foerster (2007) estimated that adult winter survivorship proportion in Brazil was 0.85 and decreased in spring; however, little is known about T. basalis adult dispersal.…”

“…In order to have a representative sample of the conditions of the field population, the 100 pairs of adult hosts were substituted by others taken from the field each time a 15–20% increase in N. viridula parasitism by T richopoda giacomellii (Blanchard) (Diptera: Tachinidae) was registered in the field. This parasitoid attacks older nymphs and young adults and its effect is a reduction in host fecundity without affecting host egg fertility (Liljesthröm, 1983; Liljesthröm & Rabinovich, 2004). Adult N. viridula density in the field was estimated by counting the total number in 30 1 m 2 -square units distributed at random in the area (for more details see Liljesthröm & Bernstein, 1990).…”

Review: classical biological control of invasive stink bugs with egg parasitoids – what does success look like?

“…Rather, several tachinid species already present in areas invaded by N. viridula formed new associations with the pest when it invaded North America ( Trichopoda pennipes ), South America ( Trichopoda giacomellii ) and the West Indies ( Trichopoda pilipes ). In most cases, these tachinids now attack N. viridula more commonly than their presumed native hosts in these areas, and parasitism levels at some points in the season can be very high (>40%) . In Argentina there were long‐term and detailed studies conducted on the impact of T. giacomellii on N. viridula populations over >20 generations of the insects .…”

“…In most cases, these tachinids now attack N. viridula more commonly than their presumed native hosts in these areas, and parasitism levels at some points in the season can be very high (>40%) . In Argentina there were long‐term and detailed studies conducted on the impact of T. giacomellii on N. viridula populations over >20 generations of the insects . Key‐factor analysis of these data suggested that T. giacomellii , via density‐dependent parasitism of N. viridula , contributed strongly to regulation of stink bug population levels, in combination with nymph mortality from predation and abiotic factors and egg parasitism by T. basalis .…”