The parasite-host relationship between Encarsia formosa Gahan (Hymenoptera, Aphelinidae) and Trialeurodes vaporariorum (Westwood) (Homoptera, Aleyrodidae). 20 Analysis of the spatial distribution of greenhouse whiteflies in a large glasshouse
1986
Noldus, L.P.J.J. (Wageningen Univ. (Netherlands). Dept. of Entomology) | Rumei, X. | Eggenkamp-Rotteveel Mansveld, M.H. | Lenteren, J.C. van
Alemán. In order to evaluate sampling methods for the greehouse whitefly, Trialeurodes vaporariorum, mathematical analyses were made of the spatial distribution of a population in a large glasshouse. The distribution of pupae was highly aggregated throughout the season. Although m/m, used as an index of aggregation, showed a continous decrease with time, the population could not be described by either the Poisson, negative binomial or Neyman type A distribution model during any of the counting periods. Comparison of the data with Taylor's and Iwoa's regression models did not yield significant correlations between variance and mean density, and between mean crowding and mean density, respectively. The spatial distribution of T. vaporariorum shows clumping at at least two levels. The change of Iwoa's rho-index with increasing quadrat size indicates that the basic components of the distribution are aggregatedly distributed compact clumps, each occupying approximately one plant. Groups of clumps, comprising several or many plants, form spatially separated patches, to which the distribution of the whiteflies in mainly restricted. As soon as the different levels of spatial clumping are considered, results of different studies of the spatial distribution of whiteflies can be better compared. Sampling method derived from studies in small greenhouses cannot be extrapolated to the level of large greenhouses, because of the essential differences in spatial distribution of T. vaporariorum at the two scales of study . A comparison of whitefly distributions in greenhouses of different sizes indicated that a whitefly population in a small greenhouse actually corresponds with a patch in a large greenhouse
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