Dispersal and Dispersion of Aphids (Homoptera: Aphididae) and Selected Natural Enemies in Spatially Subdivided Greenhouse Environments

Abstract

Matrices of potted plants within greenhouses generate spatially subdivided habitats that may influence the spread of arthropod pests and the abilities of natural enemies to locate them. Thus, the goals of current research were to quantify dispersal of the aphids Myzus persicae (Sulzer) and Aphis gossypii (Glover) in potted chrysanthemum [ Dendranthema grandiflora (Tzvelev)] greenhouses; assess the relationship between dispersal capabilities and population dispersion of aphids; and determine the influence of spatial structure on the behavior of 2 aphid natural enemies, Chrysoperla rufilabris (Burmeister) and Aphidius colemani Viereck. Replicated studies conducted in greenhouses revealed no significant differences between M. persicae and A. gossypii displacement distances, diffusion constants, and dispersion indices. Studies of the effects of localized aggregations on M. persicae population dynamics revealed decreasing rates of population increase with increasing aphid densities. Natural-enemy displacement distances and diffusion constants were significantly greater for adult A. colemani compared with 3rd instars of C. rufilabris . In addition, the percentage of A. colemani observed to be actively searching for aphids was significantly higher than the percentage of C. rufilabris larvae. Differences in dispersal capability and searching activity may explain why A. colemani successfully located 97% of all aphid-infested pots compared with the 49% located by C. rufilabris within 10 h of their release. These results suggest that aphid biological control in chrysanthemum greenhouses may be enhanced by releasing sufficient numbers of natural enemies from points ≈2 times their displacement distance 10 h after their releases. These distances are 325 cm apart among benches for A. colemani and 68 cm apart within benches for C. rufilabris .