[Experimental analysis of dormancy in the deutonymphs of the predacious manure-inhabiting mite Parasitus coleoptratorum (Acar: Mesostigmata) : A contribution to the control of development rhythm in transitory biochorions].

The control of development rhythm in inhabitants of transitory biochorions was investigated using the manure-inhabiting predacious mite Parasitus coleoptratorum (L. 1758, sensu Oudemans, 1908). The development of the deutonymphs, both the permanent and diffusion stage of this species, is almost arrested outside the manure substrate in spite of food availability (Enchytraeidae) and high humidity. If they are brought into contact with fresh horse droppings, molting follows within 2-3 days. Based on the observations of Rapp (1959) I attempted to analyze this control of development experimentally. 1. When the deutonymphs are kept in high humidity and well fed, a molting, rate of 8.2% can be observed within 3 days. If they are brought into contact with fresh horse droppings, a molting rateof 13.5% is noted within 3 days. If they are brought into contact with fresh horse droppings together with Enchytraeidae, a molting rate of 86.4% is noted in the same amount of time. Cooperating relationships must exist between these two factors. 2. The molting of the deutonymphs takes place only after a certain increase of size of the body. This is probably the trigger for molting. Environmental factors control the development indirectly by determining the speed of growth. When the deutonymphs are kept in horse droppings together with worms, the body size increases 11.6% within 18 hrs, if they are fed outside of the manure substrate the size increase is 2.5% within 72 hrs. Under these circumstances molting can be explained by an increased food intake. 3. The effect of the manure can be shown by experiments in which individual limbs are eliminated. Amputation of a pair of moving legs causes no significant change in the molting rate. This is probably based on the lack of regeneration in Parasitus coleoptratorum. However, amputation of the first pair of legs and the pedipalps, and therefore of the most important chemoreceptors of the mites, causes a delay in molting, as does the amputation of chelicerae, which hinders feeding. 4. The investigation of various qualities of the \ldmanure stimulus\rd shows that the effective factors must be gaseous decomposition products, that are still present after extensive decay. Ammonia can simulate and adequate stimulation within limits. 5. The dormany of the deutonymphs of Parasitus coleoptratorum is a nutritive quiesence superimposed by an indirect chemical control factor, alien to the food.