First, it should be noted that this discussion does not deal with circadian rhythms. This is because, in the correct sense, such rhythms can be observed only when organisms are exposed to constant conditions of light or dark.

In the medium duration LD regimes, the activity patterns of the fifteen species fall principally into two categories - light-active and dark-active - with most activity ceasing in, and perhaps being suppressed by, the opposite condition. Also applicable to most of the species, and indeed to almost all mosquito species for which laboratory-recorded activity has been reported, is that in median LD regimes distinct sharp peaks of activity are the norm. Similarly, activity is to some extent bimodal with an E/E' and M/M' pattern. Less common is a pattern with an N peak or a midday peak.

A notable variation seen with two of the wild-caught species, Ae. cinereus and Ae. punctor, is that, although there was bimodal activity with peaks following the changes in illumination, the activity actually began and ended either side of both light-off and light-on. Both also had some low level activity in light and dark. The most likely explanation is that these are true crepuscular species and the 70 lux experimental light was of the same order as the light intensity at which natural field activity takes place. Most of the Ae. cinereus adults were reared from larvae, so the activity patterns cannot be attributed to variations in age, etc., between field caught adults. The validity of the activity patterns under laboratory conditions is confirmed by the similarity with field reports. The laboratory recordings also show great consistency between individuals and from day to day, and reliable results were obtained when even only a few individuals were available for study.

The effect on activity patterns of the more extreme LD regimes is complex and not easily visualised from the basic plots of activity over several 24h-cycles shown in these Appendices. The issue, therefore, is dealt with in the main Section 1. It suffices here to note that, apart from Ae. aegypti LSHTM (Taylor & Jones, 1969) and the author's outline reports for An. farauti (Taylor, 1969b) and Cx. p. quinquefasciatus (Taylor, 1977), the use of LD regimes other than LD 12:12 has been reported for only one of the species, Cx. p. quinquefasciatus (Jones, 1982). Leaving aside the question of the E peak (see the individual species' description), the report by Jones showed that in LD 6:18 there was evidence of the M peak occurring early in long D and suggested that it came 13-15h after the light-off or the E peak.

Finally, a variable factor that might have influenced the results is that in some species the pattern of female activity changes after insemination. With the most likely exception being An. farauti, which does not mate readily in captivity, the results for the laboratory-reared specimens were almost certainly the post-insemination patterns. This is because the rearing was in a 2-foot-cube cage, there was no separation of sexes, and the adults mostly were not transferred to the recording chambers until 5-6 days after emergence. The Ae. aegypti females were examined and found to be mated (Taylor, 1969a). The wild-caught females were trapped using the author as bait and again can be presumed to be inseminated. In terms of the species covered in this paper, the effect of insemination has been examined only for Ae. aegypti (Jones, 1981), An. stephensi (Rowland, 1989) and Cx. p. quinquefasciatus (Jones & Gubbins, 1979). The post-insemination pattern of activity in all three species in LD 12:12 (the sole regime examined) was similar to the respective pattern in this paper. In the case of Cx. p. quinquefasciatus the similarity is in the N peak, which is manifest after insemination, and the presence of an E peak in the GAMBIA strain (Jones & Gubbins, 1979) but not in the LAGOS strain is an unresolved question.

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

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