Ecological and biological studies on Aedes cantans (Meig.) (Diptera: Culicidae) in southern England.
Abstract
Laboratory and field studies were carried out for 6 years on the ecology of Aedes cantans (Mg.) in southern England. Females oviposited in the leaf litter of shaded temporary woodland pools in June-September, and the eggs remained until the beginning of January in obligatory diapause that was probably initiated by reduced temperature and day-length. The larvae hatched in January and pupated in late April or early May. Comparison of numbers of viable eggs in leaf-litter samples in December with catches in emergence traps in April-May showed that about 95% mortality of overwintering immature stages occurred. Larval mortality rates decreased progressively with each successive instar. Coelomomyces fungi, an iridescent virus, mermithid nematodes, predacious dytiscid larvae and predacious flies caused some mortality of A. cantans, but the main mortality factor could not be found.In populations sampled by sweep-net, suction traps and human bait, the age-structure, seasonal abundance and incidence of sugar- and blood-feeding by females were studied; from this it was found that nulliparous females fed at first on sugary secretions and did not take a blood-meal until about 3 weeks after emergence and that some remained nulliparous after 8 weeks. Unfed nulliparous females had ovaries in stage II, and some required 2 blood-meals for complete ovarian development. Biting occurred mainly just after sunset, reached a peak in July and extended from June to September.In laboratory populations of A. cantans fed on rabbits, the times required for digestion of a blood-meal at different temperatures were determined. Fecundity declined with decreasing adult size or with the number of ovipositions by each female. Blood was usually digested after 8-9 days, after which about 32 eggs were laid. Some 15 days were required for embryonic development, after which the eggs remained viable for months or years if the relative humidity was at least 85%. The effect of continuous or repeated soaking on the hatching pattern of the eggs, and the effect of temperature on the duration of larval instars, was also investigated.<new para>ADDITIONAL ABSTRACT:<new para>Ecological studies in southern England identified mermithid nematodes as one of several factors responsible for larvel mortality of Aedes cantans.