S. Mahunka szerk.: Folia Entomologica Hungarica 44/1. (Budapest, 1983)

DISCUSSION The most surprising results of this research are the great divergence of morphological characters between the two populations investigated and the large difference in character variability between sexes. To analyze further the divergence it is necessary to appreciate the difference in the background of the populations investigated. Very little is known on the "field population" apart from the fact that is was collected on apple trees at various locations during a period of about two years. Mites of the laboratory population were at least for one generation reared in hollowed microslides on moulds with a considerable degree of inbreeding due to frequent sister x brother or mother x son mating (SUSKI, 1972a). This one can safely assume that field collected mites were fed on more diverse and plentiful food and that they were less inbred than the laboratory ones. The authors feel that difference in food conditions might solely explain character divergence between field and laboratory females. The last ones were as a rule smaller than the former with respect to general size and to dimension of each particular character. This hypothesis is well supported by the fact that most of the measurements were positively correlated with the size of the body. The only exception is the length of the distal seta on the subapical segment of leg IV (character No. 57) which is larger in laboratory mites yet it is positively correlated with the size of the body and shows relatively moderate variability (CV = 6.1% to 8.08%). This difference might be possibly due to gene recombination under inbreeding conditions. This simple explanation seems not sufficient for males which demonstrated much greater divergence between field and laboratory populations and a much greater variability within each population than the females. We feel that arrhenotokeous mechanism of sex determination might be at least partially responsible for those differences. It was found that males develop from unfertilized eggs in this and in several other tarsonemid species (SUSKI, 1968, 1972a). Thus males are most probably haploid which facilitates the phenotypic manifestation of all the variability genetically determined. The results provide some bases to evaluate the taxonomic value of characters investigated. In general it might be assumed that characters demonstrating large variability and or readily altered by breeding condition or mounting procedure are less valuable from the taxonomist point of view. If this assumption i3 sustained, direct measurements of morphological structures seem less suitable for taxonomic purposes than their ratios. Among direct measurements those taken along the surface of sclerotized exoskeleton are more stable thus more reliable as taxonomic features than the ones pertaining to lengths of setae. This is not surprising because those flexible structures are quite difficult to measure exactly and they are readily distorted in mounting. Male characters seem less suitable for taxonomic purposes than female ones. Particularly variable structures are on legs IV of the male which depreciates their value as taxonomic characters. The smallest variability of morphological structures is displayed on ventral plates. This is particularly true for females with an exception of tegula which seems rather variable. This small variability suggests that those structures might present a greater value as taxonomic characters. These studies concern a single species only. It is difficult therefore to generalize the results. However, LINDQUIST (1978) reports a comparable variability of morphological characters in Tarsonemus waitei Banks. In this case also male characters, particularly those pertaining to legs IV seem more variable than any other group of characters on a female. Besides, authors of the present paper very often have observed a greater variability within other tarsonemid species whenever larger series of specimens were examined. In fact not very seldom it was difficult to decide whether the specimen under examination still belongs to a particular species or it should be described as a separate taxon due to differences in the size, appearence of leg IV, chaetotaxy, etc. The authors feel, therefore, that female specimens are more convenient and reliable for identification than male ones. This is still emphasized by the well-known fact that females are much more abundant in nature than males. Furthermore, the authors are of the opinion that descriptions of new species as well as taxons of a higher order should be based principally on female specimens; preferably on syntype series consisting of five or more specimens rather than monotypic. We feel also that it should be avoided as much as possible to erect new taxon based solely on male specimens unless large syntype series are available and/or they demonstrate really stricking features.