Further Research for Mite Behavioral and Evolutionary Ecology
Evolutionary ecology and sociobiology are sciences for studying the selection pressures operating in nature. As I have described, I believe that spider mites and phytoseiid mites are ideal materials for such studies, because they are often directly exposed to natural selection. Their short life spans and our ability to observe their entire life cycle in small experimental areas are also great advantages. By these and other merits, we have been able to conduct much of the research described so far.
However, there are also some difficulties involved in using mites for ecological studies. Each trait of the species that we focus on, the nesting behavior of St. longus, for example, has to be checked against every kind of selection, i.e., natural selection operating on survival and reproduction, sexual selection on mating success, and synergistic and/or kin selection on social living, all of which must be operating simultaneously in natural habitats. The minute bodies of mites often make it impossible to observe individual lifetime success in the field. Furthermore, environmental conditions surrounding such minute organisms may be quite different from our own sense of realism, as pointed out by Schmidt-Nielsen (1984) and Saito and Suzuki (1987). Difficulties underlying the study of spider mite genetics must be also mentioned. Saito et al. (2000b) revealed that there are recessive genes that govern the depression of female fecundity (Chap. 5). However, they could not determine how many genes (alleles and loci) are responsible for this trait or how intense this effect is in comparison with the wild type. To acquire such information, we have to observe the fitness changes between generations under constant conditions without environmental variance. Because spider mites are phytophagous, it has been (and still is) difficult to keep host plant conditions constant. Therefore, we still have only limited means of obtaining this important information. It is necessary to develop some kind of artificial diet that can keep the food conditions of spider mites constant to overcome such a hurdle.