An important malaria vector species of primarily South Asia, found between latitudes 10°N and 35°N. The type locality was Ellichpur, Central Provinces, India. Its northern limits probably are defined by the 10°C isotherm, as at that temperature development effectively ceases and eggs will not survive exposure to lower temperatures for more than two weeks (Lal, 1953; Stone et al., 1959; Al-Tikitry, 1964). Daggy (1959) found that in the oases of Saudi Arabia the adult females sheltered by day and fed only after sunset.

Experimental material
The adults were reared, under LD 12:12, from eggs obtained from the Ross Institute of Tropical Medicine, where a colony originating from near Delhi, India (28°39'N), had been maintained since 1950. The colony was of the strain StSSDPI.

Experimental regimes
LD 8:16 to LD 4:20, nine females, studied from 3 days post-emergence (18 October 1968). Recorded in LD 8:16 for days two to five then light-on delayed 4h to give LD 4:20 until day eight.
LD 12:12 to LD 16:8, nine females, studied from 3 days post-emergence (18 October 1968). Recorded in LD 12:12 for days two to four then light-on advanced 4h to give LD 16:8 until day eight.
LD 20:4, nine females, studied from 5-6 days post-emergence (24 October 1968) and recorded for days three to six.

Results and discussion
The activity patterns are shown in Figure A9 below. In all five LD regimes there is a major E peak, with low level activity through much of the dark period. M peaks are clear at light-on in LD 12:12 and LD 16:8, and there is a response to light-on in LD 20:4. The continuation of activity after light-on in LD 20:4, specially in the second 24h cycle, may suggest that M is more than just a startle response to light-on.

Figure A9

From field studies in Punjab Province, Pakistan (approx. 32°N), Reisen & Aslamkhan (1978) found that the peak of biting was markedly crepuscular during periods of low ambient temperature (i.e. a peak at 1800-1900h in November to February) but this shifted with increasing ambient temperatures, being around 2200-2300h in May to July.

Jones (1974) recorded An. stephensi flight activity in the laboratory. His results in LD 12:12 also showed the bimodal pattern, with a strong E and a lesser M, seen in Figure A9 and previously outlined by Taylor (1969a, b). He found additionally that, in DD following LD 12:12, there was a clear circadian rhythm, although only E persisted, with a circadian period t < 24h. Using LD 12:12 to 24h L to DD, the activity was reset by light-off and the new rhythm persisted.

More recently, Rowland (1989) has used the acoustic technique to examine several aspects of the An. stephensi flight activity. His work differed in using a regime with light of 40 lux and "dusk" simulated by a transition period dimming the light to 0 lux over a period of one hour. The transition from L to D was measured at an undefined mid-point, presumably 20 lux. Changes in the flight activity pattern associated with insemination, blood-feeding, oviposition and nocturnal light intensity (artificial moonlight) were detected by recording the patterns before and after mating, and throughout the gonotrophic cycle. Males and virgin females showed only E activity in LD 12:12. After insemination females exhibited an E peak followed by short bursts in the night (similar to those shown in Figure A9). After blood-feeding the females were inactive for two nights, but once gravid there was strong E activity and lesser activity later in the night. After oviposition the females resumed the post-mating pattern. The effect of simulated moonlight was an apparent movement of E and enhanced, prolonged N activity. Rowland also found a circadian rhythm in DD, with t @ 24h.

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