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Darkness induces mobility, and saturation deficit limits questing duration, in the tick Ixodes ricinus

Jean-Luc Perret, Patrick M. Guerin^*, Peter A. Diehl, Michéle Vlimant and Lise Gern

Institute of Zoology, University of Neuchâtel, Rue Emile-Argand 11, 2007 Neuchâtel, Switzerland

View larger version (15K): [in a new window]   Fig. 1. Frequency plots of walks by I. ricinus nymphs recorded at intervals of 3 s over 10 days with a photoperiod of (A) 14 h:10 h L:D (N=58 nymphs) and (B) 8 h:4 h L:D (N=49 nymphs) at 25°C and 60% relative humidity. Light cycles are indicated by the broken lines, with full intensity beginning at 10.00 h in A and at 10.00 h and 22.00 h in B.

View larger version (15K): [in a new window]   Fig. 2. Frequency plots of the duration of questing events by I. ricinus nymphs at saturation deficits of (A) 9.3 mmHg, (B) 3.5 mmHg and (C) 1.9 mmHg (1 mmHg=133.3 Pa). Questing duration decreases with increasing saturation deficit (Jonckheere test, P<0.05; see text for details).

View larger version (16K): [in a new window]   Fig. 3. Frequency plots of the duration of quiescence events by I. ricinus nymphs at saturation deficits of (A) 9.3 mmHg, (B) 3.5 mmHg and (C) 1.9 mmHg (1 mmHg=133.3 Pa). Most events are shorter than 24 h (grey bars). Quiescence duration is not related to saturation deficit (Jonckheere test, P=0.93; see text for details).

View larger version (34K): [in a new window]   Fig. 4. Pooled frequency plots of I. ricinus nymphal questing, walking and quiescence start (top) and end (bottom) times over 10 days in a 14 h:10 h L:D cycle under three climatic conditions (see text). The light cycle is indicated by the broken lines, with full intensity beginning at 10.00 h. Totals of 322 quiescence, 143 questing and 541 walking events were recorded for 95 nymphs (see text for further details).

View larger version (83K): [in a new window]   Fig. 5. Photoreceptor cells of the tick I. ricinus. (A) Optical and electron microscopical examination of larval (L), nymphal (N), adult male (M) and adult female (F) I. ricinus revealed 20–21 bilaterally arranged photoreceptors, each placed dorsolaterally posterior to coxa 2; axons from the photoreceptor cells form the optic nerves (ON) that pass antero-laterally to reach the synganglion (SYN) rostrally; S, spiracle. (B) Photoreceptors (1–10) of a larva, located immediately below the cuticle (CU) and the hypodermis (HY). (C) A larval photoreceptor cell containing a major rhabdomere (R), attached to the hypodermis (HY), lysosome (L), mitochondria (M) and nucleus (N).