Delphastus catalinae and the silverleaf whitefly, Bemisia tabaci biotype B, on tomato: modeling predation across spatial scales

Understanding behavioral traits that determine the ability of predators to suppress pest populations at spatial scales larger than those evaluated in the laboratory may help in selecting the right species and release rates for biological control programs. My thesis is that predation rates within whole plants are driven by the interaction between prey distribution, individual predator patch-to-patch behavior and consumption rates within patch units. I propose that results derived from simple laboratory settings can be useful to predict predation rates within whole plants, if they are combined with spatially explicit descriptions of prey distribution and predator movement patterns. I assume that the leaflet is a spatial scale at which predators and prey behave as in laboratory settings, at least in experiments without replacement of consumed prey. My study extended from the leaflet to the plant scale, encompassing both the relatively homogeneous prey patch unit, leaflet, and the more structurally complex combination of leaflets, leaves, branches and main stem.;My study system consisted of the silverleaf whitefly (SWF), Bemisia tabaci biotype B, and the coccinellid predator Delphastus catalinae inhabiting greenhouse tomato plants. To support my thesis, I evaluated key predator behavioral patterns by modeling the interaction between SWF spatial distribution and the search behavior of D. catalinae. First, I developed an algorithm to generate within-plant spatial distributions of the SWF, based on aggregation patterns observed within and among tomato leaves. Second, I described the spatial interaction between the SWF and D. catalinae at the within-plant scale and examined its effects on D. catalinae predation rates and functional response. I found that prey and predator prefer different plant regions and that predation rates and the functional response at the scale of a leaflet are comparable to what have been observed in the laboratory. In contrast, I observed that predation rates are lower and that the functional response changes qualitatively when the scale of observation is increased from the leaflet to the plant. To gain understanding of the processes that drive such a change in predation rates and functional response with scale transition, I developed an individual-based model that incorporates the observed behavioral patterns of D. catalinae individuals when preying on SWF nymphs within tomato plants. I found that the number of leaflets visited per plant by predators and the degree of spatial alignment between predator and prey distributions impact predation rates significantly at the spatial scale of the whole plant. Also, I demonstrated that simple measures of prey distribution and predator foraging patterns can be used to scale up functional responses estimated through laboratory settings. Altogether, my research shows that non-random distributions and movement patterns of prey and predators can be predicted, at least within plant structures, and that simple measures of such patterns can be used to accurately model predation rates within plants using observations from laboratory settings. My thesis can be applied to overcome current limitations in the extrapolation of data collected in the laboratory to the field, which ultimately will help fine-tune release procedures of biological control programs.