Biological rhythms and vector insects.

The adjustment of all species, animals and plants, to the Earth's cyclic environments is ensured by their temporal organisation. The relationships between parasites, vectors and hosts rely greatly upon the synchronisation of their biological rhythms, especially circadian rhythms. In this short note, parasitic infections by Protozoa and by microfilariae have been chosen as examples of the dependence of successful transmission mechanisms on temporal components.

Biological rhythms and vector insects

The adjustment of all species, animals and plants, to the Earth’s cyclic environments is ensured by their temporal organisation. The relationships between parasites, vectors and hosts rely greatly upon the synchronisation of their biological rhythms, especially circadian rhythms. In this short note, parasitic infections by Protozoa and by microfilariae have been chosen as examples of the dependence of successful transmission mechanisms on temporal components.

Reproductive and post-embryonic daily rhythm patterns of the malaria vector Anopheles (Kerteszia) cruzii: aspects of the life cycle.

Females of Anopheles (Kerteszia) cruzii, a sporadic malaria vector in some areas of the Atlantic Forest in south and southeastern Brazil, were captured and studied under controlled conditions. In the laboratory, daily observations were conducted in natural light-dark cycles at 25.1+/-0.6 degrees C and relative humidity 57-81%. Post-embryonic development, which comprises four larval instars and the pupa, was continuously observed, and its cycles, as well as temporal components of reproduction, were registered. A preliminary study on female longevity was also performed. Oviposition, ecdysis from the third and fourth instars larvae, and pupation were visually monitored over three consecutive days and the emergence of adults over four consecutive days. Results were analyzed by circular statistics, and the null hypothesis of the absence of rhythm was assessed by Rayleigh's test at the 5% significance level. From a total of 141 females captured, 113 (80.14%) survived and 79 (69.91%) were successfully fed on blood, offered at one of two time intervals, 09:00-10:30 h (morning) or 18:30-20:00 h (evening). A total of 36 females laid 1063 eggs in 65 oviposition episodes, and 18 females presented fragmented oviposition. The average duration from egg-laying until adult emergence was 30.71+/-3.57 days, the larval stage being the longest in the post-embryonic development. Egg-laying showed a daily rhythm, with a peak at 23:24+/-3:47 h, 2 to 5 h after sunset. The time of the blood meal did not shift the phase of the egg-laying rhythm. The last larval ecdysis, pupation, and adult emergence did not follow a 24 h rhythmic pattern. A description of temporal patterns of post-embryonic development, particularly in the case of vectors, can be an important tool in research to determine methods of control.