Although flight is an essential precursor to almost all the normal functions of adult mosquitoes, relatively few species feature in published results from laboratory studies of the daily patterns of flight activity. When the recordings described in this paper were made there were only three examples.

Interestingly, the first was among the earliest scientific observations of a circadian rhythm. Roubaud (1918) studied the physiological rhythms and spontaneous flight in Anopheles maculipennis sensu lato. Using an undescribed method, he found that, in a normal 24h cycle of light (L) and dark (D), activity was confined to the first 2h of the night, with the remaining 22h being spent in a state of complete rest. In constant dark (DD) the mosquitoes initially advanced their hour of flight by up to 1.5h per day but this rhythm later stabilised to give an onset of activity some 2-4h ahead of the normal onset in a light-dark regime (LD). In constant light (LL) the cycle was inhibited. Roubaud concluded that a fundamental rhythm was responsible for preparing the mosquito to commence activity when the light intensity dropped sufficiently.

The second example was the work of Bates (1941) on Anopheles superpictus. He made half-hourly visual observations of flight activity in continuous dim light, following a regime in which each L consisted of 0.5h dim light, 12h bright light and 2h dim light. In an LD regime coincident with the normal solar day and in a reversed DL regime, the activity in dim light proved to be cyclic with the onset of active periods at about 24h intervals. From a parallel experiment in DL, however, he noted that the activity of Aedes aegypti seemed to be entirely random.

The third example was the start of studies of Anopheles gambiae (Jones et al., 1966, 1967). This followed the development of automatic recording techniques (Jones, 1964) which facilitated intensive studies - particularly at Brunel University, including those described in this paper (which were part of the author's post-graduate research programme, Taylor, 1969a), and later at the University of Sussex. The method also has been used at The London School of Hygiene and Tropical Medicine. Almost all the studies have relied on event recorders using a paper trace, but the relative insensitivity and the need for tedious manual transcription have limited the analysis and interpretation of the activity cycles. The only other extensive series of papers has come from Japan, where a photoelectric detector system was used.

The principal publications of the modern era are on the following species:- the primarily African malaria vector Anopheles gambiae (Jones et al., 1966, 1967, 1972a, b, 1974; Jones & Gubbins, 1977, 1978; Mnzava & Curtis, 1989; Rowland, 1991); the Yellow Fever vector Aedes aegypti (Taylor & Jones, 1969; Jones, 1981; Rowland & Lindsay, 1986); the filariasis vector Culex pipiens quinquefasciatus (Jones, 1976; Jones & Gubbins, 1979; Peterson & Jones, 1979; Peterson, 1980a, b, c; Jones, 1982) and other members of the Culex pipiens complex, pallens and molestus (Chiba, 1964; Chiba et al., 1981, 1982, 1990, 1992; Kasai & Chiba, 1987; Chiba & Tomioka, 1992; Shinkawa et al., 1994); the south Asian malaria vector Anopheles stephensi (Jones, 1974; Rowland & Boersma, 1988; Rowland, 1989, 1991); Aedes flavopictus (Chiba, 1971); Culiseta incidens (Clopton, 1984, 1985); Aedes taeniorhynchus (Nayar & Sauermann, 1971); and, Armigeres subalbatus (Song & Ke, 1989). Although the list may seem quite extensive, most studies have focused on basic activity patterns under LD 12:12 regimes, together with activity in LL and DD. The commonest expansion has been into the effects of insemination, blood feeding, and parasite loads.

This paper describes the patterns of activity for fifteen species which were recorded in a range of LD regimes. The results were presented in summary form in the author's doctoral dissertation (Taylor, 1969a) and some were similarly shown or referred to in short published reports (Taylor 1969b and Taylor 1977). The initial research was on a long-established laboratory strain (LSHTM) of Aedes (Stegomyia) aegypti (Linnaeus) subspecies aegypti (originally from West Africa in 1926) and followed conventional lines of examination of the underlying circadian rhythms (in LL and DD), together with phase-reversal and resetting experiments. These largely confirmed the findings of earlier studies of circadian oviposition rhythms (summarised by Gillett, 1962) which had indicated that light-off was the sole phase-setting influence, or zeitgeber, in the light-dark cycle. Use of extreme LD regimes (especially LD 20:4), however, led to an unexpected conclusion that both light-on and light-off had phase-setting effects. It was suggested that these appeared to reinforce each other in a range of photoperiods coinciding with that of the natural geographical range of the species (Taylor & Jones, 1969).

It was with the primary objective of testing the latter concept that the experiments described in this paper were carried out. Here the activity is plotted as a score per half-hour, rather than the scores per hour used previously (Taylor, 1969a, b, 1977; Taylor & Jones, 1969). The records of LSHTM in LD 4:20, LD 12:12 and LD 20:4 are re-presented, together with results from LD 8:16, LD 14:10, LD 16:8 and LD 18:6. The activity patterns in five LD regimes are shown for three other strains of Aedes aegypti; one, Ilobi, of the type form ssp. aegypti, originally from Southwest Nigeria and in culture for ten years; and two strains of the "wild-form" ssp. formosus from Uganda - Bwamba, only six-months in culture, and West Nile, in culture for two years.

Of the fourteen other species, activity in a range of five or more LD regimes was recorded for:- Aedes (Ochlerotatus) punctor (Kirby) (British); Anopheles (Anopheles) atroparvus van Thiel (Dutch); Anopheles (Cellia) farauti Laveran (Australasian); Anopheles (Anopheles) plumbeus Stephens (British); Anopheles (Cellia) stephensi Liston (South Asian); Culex (Culex) pipiens pipiens Linnaeus, for both summer and winter generations (British); and, Culex (Culex) pipiens quinquefasciatus Say (African).

The other species, which were observed in fewer LD regimes are :- Aedes (Aedes) cinereus (Meigen) (British), Aedes (Ochlerotatus) detritus (Haliday) (British); Aedes (Finlaya) geniculatus (Olivier) (British); Aedes (Ochlerotatus) impiger (Walker) (Canadian); Aedes (Ochlerotatus) nigripes (Zetterstedt) (Canadian); Coquillettidia richiardii (Ficalbi) (British); and, Culex (Culex) torrentium Martini (British).

Separate Appendix pages give the activity graphs, experimental details and biogeographical information for each of the species. The main text is divided into Section 1, where a double plotting method, the photoperiodogram, is used to present comparative displays of the distribution of percentage activity in each half-hour of every 24 h light-dark (LD) cycle in a range of LD regimes; and Section 2, where the development of a multi-clock concept capable of underpinning the actvity patterns found in LD regimes other than LD 12:12 is given. All the Section pages and the Appendices, together with the References are listed in the .

Throughout the paper conventional srl links enable rapid sourcing of information, figures, etc. Although the individual species information and results can be accessed directly from the "Contents", following the sequence linked by the button is suggested, especially in Section 2, where the multi-clock concept is developed sequentially.

Section 1

©1998, 2010 - Brian Taylor CBiol FSB FRES 11, Grazingfield, Wilford, Nottingham, NG11 7FN, U.K. Comments to dr.b.taylor@ntlworld.com

href="\crhtml\intro.htm"