N. Hinomoto et A. Takafuji, STUDIES ON THE POPULATION-STRUCTURE OF THE 2-SPOTTED SPIDER-MITE, TETRANYCHUS-URTICAE KOCH, BY ALLOZYME VARIABILITY ANALYSIS, Applied Entomology and Zoology, 29(2), 1994, pp. 259-266
Electrophoretically detectable variation in phosphoglucoisomerase (PGI
) was found in a Tetranychus urticae population on vinyl-house strawbe
rries. Three types of band patterns were present in this population, i
ndicating that two alleles exist at the PGI locus. Frequencies of the
genotypes were determined at five different levels of sub-population (
leaflet, leaf consisting of 3 leaflets, patch of injured plants, sub-d
ivided section and the whole house). The proportion of sub-populations
which deviated from HARDY-WEINBERG equilibrium was smallest at the le
aflet level, and increased with the size of the sub-population. In con
trast, the proportion of sub-populations that were monomorphic was gre
atest at the leaflet level. Further, WRIGHT's F-statistics were calcul
ated at each of the levels. At the leaflet level, the inbreeding coeff
icient (F(IS)) was smallest, whereas the fixation index (F(ST)) was gr
eatest. The F(IS) for the whole population was about 0.5. These result
s suggest that the mites tend to form breeding colonies on individual
leaflets. However, because random genetic drift easily occurs within e
ach colony when population size is small, the whole population is thou
ght to maintain a large degree of genetic diversity.