Published online by Cambridge University Press: 31 May 2012
Population growth and dispersion of Tetranychus mcdanieli McGregor were studied in an experiment conducted on Red Delicious apple trees grown in a light and temperature controlled walk-in growth room. Lloyd’s index of mean crowding was calculated as a means of interpreting aggregation patterns; however, it was found that mean colony size
was a more generally useful population parameter
. The regression of
on mean density (m) and the ratio of mean density to
were used to determine and characterize the patterns of dispersion obtained under the experimental conditions of the study.
It was shown that the ratio of mean density to is the proportion
of sampling units (i.e. individual leaves) that would have a colony size of
individuals per unit, all other units being unoccupied. Characterization by the concomitant parameters
and
provides a more sensitive and meaningful method of describing populations than does the arithmetic mean.
The data indicated that adult female populations of T. mcdanieli tend to be distributed as clumped colonies on apple trees. A plant feeding mite damage scale was devised to evaluate the reliability and accuracy of gross observational estimates as indicators of spider mite levels.