Behaviour of the Red-Legged Earth Mite, Halotydeus destructor, in Relation to Environmental Conditions

1. The reactions to the physical and chemical stimuli to which the phytophagous mite (Halotydeus destructor) is exposed were observed and tested experimentally; also the effect of these stimuli on the special activities such as host-plant selection and oviposition. 2. The mite is positively phototropic, except when in very bright light, such as strong sunlight; if no bright source of light is visible, the mite selects a subdued light, avoiding bright light and darkness. 3. It avoids extremes of temperature, but between these limits its selective activity is not marked; the higher the temperature, the greater is the mite's activity. 4. It has no strongly developed selective behaviour in relation to atmospheric humidity; but is more active, the lower the humidity; it selects a moist soil; free water is usually avoided. 5. There is no geotropic reaction, except that for oviposition the underside of a horizontal surface is preferred. The palps and forelegs serve as tactile organs; the mite is attracted by the feel of some surfaces, repelled by that of others; it is stereotropic under favourable physical conditions; it is made restless by vibration; there is no anemotropic reaction. 6. It is attracted by the taste of some sweet substances but is indifferent to others. It is repelled by the vapours of many volatile substances. 7. Host-plant selection is the result of random wandering with repeated trial-and-error testing of the substratum by means of tactile and gustatory organs. 8. The crowding together of the mites into dense clusters seems to be a tactile reaction, but occurs only when physical conditions are favourable. 9. Web-spinning is probably a male characteristic and depends to some extent on the presence of moisture. 10. In the selection of oviposition-sites (the undersides of Cryptostemma leaves are preferred), texture, moisture and position are important factors, taste and light are not important, while a high temperature (about 28 degrees C.) puts a stop to all further oviposition. 11. In general, the activity of the mites under certain favourable conditions is subdued, and they usually crowd together. But conditions (internal and external) at most times depart to some extent from the optimum range; this calls forth the more vigorous activity of running, with occasional turns, and frequent testing of the substratum by means of tactile and gustatory organs. This is the basis of the action system, for reactions to special stimuli consist of modificat