PREY CAPTURE AND FACTORS CONTROLLING TRAP NARROWING IN DIONAEA (DROSERACEAE)

Traps of Dionaea which have captured prey by a rapid closure mechanism continue to close with the lobes of the trap assuming a tightly appressed condition called the narrowed phase. Traps fed ants, which make up about one-third of the prey captured in the field, assumed the narrowed condition within about 7 h of feeding. Ants were alive and capable of delivering mechanical stimulation to the trigger hairs until about 8 h after feeding when they were apparently killed by acid fluid (pH 2–3) secreted by the trap at that time. That stimulation of trigger hairs delivered by the insect during this period is sufficient to cause both the narrowing and acid secretion was demonstrated by laboratory experiments in which both of these responses were initiated within 5 h by stroking the trigger hairs with clean, dry nylon bristles. Such purely mechanical stimuli, delivered to the trigger hairs, produced action potentials in the trap throughout the period of stimulation. Chemicals such as Na⁺, NH₄⁺, urea, and amino acids were capable of producing the narrowing response within one or two days. There was a 50% response to NaCl and NH₄Cl solutions of about 6 mM and a 90% response to 34 mm solutions. Urea, L-lysine, and glycine produce a significant response at 50 mm but can cause necrosis of the trap tissue at concentrations above 50 mm . Salt-free ovalbumen (0.5 and 5.0 g/l) and KCl, CaCl₂, and D-glucose were ineffective in initiating the narrowing response. The level of Na⁺, NH₄⁺, and amino acids necessary to elicit the narrowing response is within the range of concentrations previously demonstrated to exist in the haemolymph and tissues of prey known to be captured by Dionaea in the field. The data is consistent with the hypothesis that narrowing and secretion are initiated by mechanical stimulation and maintained by chemical stimulation after the death of the prey.