Gut expansion and contraction in the predatory soil mite Pergamasus longicornis (Mesostigmata: Parasitidae): a stiff system.

Mite digestive processes are inferred from gut expansion and contraction time in the free-living predatory soil mite Pergamasus longicornis (Berlese), estimated using a temporal series of histological sections. Gut regions (bar the rectal vesicle) behave broadly in unison for rapid initial filling (ingestion half-life about 2-3 min; max 8 min), but behave heterogeneously when slowly emptying (digestion/egestion half-life from about 2-3 h; max 8.5 h). Anterior gut regions fill and empty the earliest. Posterior gut regions take the longest to fill and to empty. Switching first from filling-predominating to emptying-predominating in the gut occurs around 2 h from the start of feeding. Median time for the initial completion of gut filling and for the commencement of gut emptying is 10 min and 12.5 h, respectively, from the start of feeding. Three phases of gut changes are critically discussed: rapid filling, concentration by fluid loss (via coxal glands), and slow emptying. Independent corroboration of coxal droplet formation is included. Predictions to confirm or refute postulated mechanisms of salivary, coxal or rectal water balance are given. Overall total gut filling (ingestion) plus gut emptying (digestion/egestion) time in this poikilotherm is approximately 29-52.5 h (1+ - 2+ days) at room temperature from the start of feeding on large dipteran prey ([Formula: see text] gut emptyings per day). Pergamasus longicornis exhibits the stiff digestive system of an intermittent 'bolus' feeder.