Dynamics of Within-Leaf Spatial Distribution Patterns of Greenhouse Whiteflies and the Biological Interpretations

Abstract

(1) The spatial distribution of insects can be approached on different environmental unit scales, e.g. between plants, within plants and within leaves. It is possible to obtain a biological interpretation of these spatial distributions of whiteflies from various aggregation indices. (2) Adults are more aggregated than all the other stages (a' (log a) and b of Taylor (1965) are equal to 0-4642 and 1-2617 respectively). This is due to pairing and the tendency of whiteflies to feed near the major veins of the leaves. Grouping of individuals is moderate while the distribution of the groups is most highly aggregated. (3) Eggs are laid in clusters, grouping of individuals is increased and the clusters are relatively sparsely distributed. As a whole, aggregation is decreased (a' = 0-3582, b = 1. 1496), yet higher than all nymphal stages. (4) Due to the relatively high mortality rate (18.6%) in the early nymphal stages and the density-dependent dispersal of the first instar nymphs, the 3rd instar nymphs are much less aggregated (a' = 0-1092, b = 1-06 10). (5) During the later nymphal stages, the nymphs suffered a high mortality rate (22.8%), which is density and crowding dependent. By the method of Taylor, the populations are approaching random but still with some degree of aggregation (a' = 0.0880, b 1-0518). In fact, most populations are random, but some are not. (6) However, Iwao's (1968) regression appears to be linear only when Taylor's b = 1 or 2. In this case, E*I-m relationships are apparently not linear, especially with adults and early stages. Thus, interpretation of the parameters a and /1 is questionable.