Phytoseiidae, A.Berlese, 1916

Tixier, M. - S., Lopes, I., Blanc, G., Dedieu, J. - L. & Kreiter, S., 2014, Phytoseiid Mite Diversity (Acari: Mesostigmata) And Assessment Of Their Spatial Distribution In French Apple Orchards, Acarologia 54 (1), pp. 97-111 : 101

Phytoseiidae distribution in apple orchards

In order to characterize Phytoseiidae distribution at the plot level, Taylor’s law has been used ( Taylor 1961). This law relates the standard deviation (S 2) to the mean (m) according to the following relation: S 2 = amb. When applying a log transformation, the latter relation describes a straight line (logS 2 = log(a) + b x log(m)), where b is the slope. The b value of this relation provides information on distribution: when b = 1, the species is randomly distributed, when b> 1 the distribution is aggregative and when b <1, the distribution is regular. To establish such a relation and calculate the b value, the mean and the standard deviation of each plot have been calculated (and log transformed) and a simple correlation test has been applied (Statsoft 2008).

Characterisation of the sample size for optimal sampling

In order to define the number of leaves to be sampled in further surveys for characterising the number of Phytoseiidae in apple orchards (N), the following relation (Nachmann 1984) was applied: N = am (b-2) /E 2 where a and b are Taylor’s law variables, m the mean, and E 2 the accepted error around the mean. We herein tested two errors: 10 % and 20 % of variation around the mean, i.e. for a mean of 0.5 Phytoseiidae /leaf that means that the samplings can provide estimation intervals of 0.45 – 0.55 and 0.4 – 0.6 Phytoseiidae /leaf, respectively.