Spatial pattern of Bemisia tabaci biotype B (Hemiptera: Aleyrodidae) nymphs on tomato plants

Understanding the spatial pattern of pest populations is crucial for the appropriate design of sampling methods, pesticide application protocols and the selection of biocontrol agents. The spatial distribution of the silverleaf whitefly (SLWF) Bemisia tabaci biotype B, one of the most important pests of tomato crops worldwide, has been studied extensively in tomato crop systems. Within plants, most attention has been paid to the vertical distribution of nymphs along plant nodes, ignoring the spatial pattern of immatures at smaller scales. The aim of this research was to describe the spatial pattern of SLWF nymphs with enough detail to develop an algorithm to simulate nymph locations within tomato plants. Different numbers of SLWF adults were released on individual tomato plants. The resulting number of nymphs per leaflet was counted and the infested leaflets were scanned to determine the relative location of the nymphs within leaflets. To develop the simulation algorithm, the distribution pattern of SLWF nymphs was described at 3 spatial scales: plants, leaves and leaflets. We found that the location of SLWF nymphs on plant nodes is well described by a beta-binomial distribution. Within leaves, nymph counts were described by a negative-binomial distribution and their locations using Distance Indices (SADIE). The overall pattern within leaflets was aggregated and the distribution was described using the distance of each individual to the midrib. The algorithm was validated using field data from the literature. The use of simulated nymph locations within leaflets, among leaflets within leaves, and among leaves within plants is discussed.