impact of environmental and entomological factors on inter-village filarial focality in the Nile Delta

The epidemiological study covered 127 and 79 houses scattered in El Qolzom [QOL] and Kafr Shorafa [KSH], respectively, and described 25 items relating to housing characters, socio-economic state and human activities. It revealed that, QOL is more rural than KSH, therefore it would be more favorable to the vector mosquito population and hence, filarial parasite transmission in QOL. Weekly records [N =81 and 62 for QOL and KSH, respectively] of ambient temperature, relative humidity and wind speed taken at sunset, over three months during summer, revealed no significant variation between villages. Those measured at sunrise revealed significant, although inconsistent, differences at a particular month, but no difference over the whole period. Whether climatological conditions could have influenced mosquito bionomics in the study villages was questionable. The ultimate outcome of observed entomological factors might explain its preponderance in QOL

Filariasis transmission potential of mosquitoes to humans of different age groups

Age-specific levels of Wuchereria bancrofti infection determined by microfilaremia in filarious 10 to 60 years old males from an endemic village revealed that microfilaria intensity was higher in younger age, presumably because of increased vector biting rate of younger individuals. Out of 1334 Cx. pipiens captured while attempting to bite 51 child-adult bait pairs, 54% selected a host in the 10 - 15 age group. Biting preference towards children was more elevated [79.2%] later than earlier in the night. Frequency distribution of age- specific biting collections indicated that 62.7% recorded exceeding numbers of bites on children, 21.6% adult biting, and 15.7% equal biting of one of the baits in the pair. Furthermore, 21.6% of the children were exposed to nightly bites ranging from 21 to 64 and only 7.8% of the adults experienced from 21 to 85 bites. Mosquito biting intensity averaged 14.2 and 11.6 bites/night for children and adults, respectively. Children experienced 22.4% more bites per night than adults. Thus, children are more exposed to filaria infection and seem to represent an important source of infection. It is concluded that attempts at widespread control of filariasis in the densely populated Nile Delta, where youngsters may account for an immense proportion of the local population should concentrate on immatures

Facultative blood-feeding by nulliparous autogenous Egyptian aedes caspius pallas [diptera: culicidae]

Facultative blood-feeding, in which nulliparous autogenous Aedes caspius females imbibed blood from a human host before laying their first egg batch, was compared in various geographic populations under laboratory conditions. It accounted for about 39% in the populations tested [range: 27 - 54%]. Temporal blood-feeding activity studies demonstrated that nulliparous autogenous females were liable to ingest blood from 1 to 6 days postemergence, although most females elected to feed when 2 or 3 days old. Ovarian development, determined at the time of blood-feeding, varied from Christopher's stage II B to stage V indicating that vitellogenesis did not inhibit blood-feeding and that the degree of maturation of the ovaries was not a limiting factor to blood-feeding of autogenous females. However significant population differences regarding ovarian stage at the time of blood ingestion were observed. Most autogenous females were half blood-fed regardless the degree of maturation of their follicles. It seems likely that many nulliparous autogenous Ae. caspius will not delay their initial blood meal until they have laid their autogenous egg batch, this would result in early repeated host seeking attempts by these mosquitoes, thereby increasing their vectorial capacity

Heterozygote deficiency in natural populations of aedes caspius pallas from Egypt

Aedes caspius Pallas populations from the Mediterranean regions are genetically highly polymorphic, and may diverge into 2 genetically isolated forms. We examined the genetic structure of 3 mosquito populations from Faiyum oasis, using starch gel electrophoresis at 8 gene loci, from which only one was monomorphic. Genetic variability was high [A = 1.97; H = 0.12; P = 54.2, 66.7]. Eleven out of 16 population enzyme combinations with variability exhibited heterozygote deficiency from Hardy - Weinberg expectations. These results suggest that tested populations represent a mosquito complex, although no genetic divergence was detected [D = 0.012] since presumed sympatric gamodemes were sampled as a single population. It is of prime importance to detect cryptic gamodemes and to elucidate the present status of Ae. caspius, as this may greatly influence control strategies

Bi-autogenous ovarian cycles in Egyptian aedes caspius pallas [Diptera: culicidae]

Autogenous Aedes [Ochlerotatus] caspins Pallas from Aswan deposits 1 to 2 egg batches without a blood meal. Repeated ovarian developmental cycles were responsible for the bi-ovipositional pattern as indicated by the presence of 2 dilatations in the ovariolar pedicel of bi-autogenous females and by the early stages of development of the ovaries [II and II B] observed 1-3 days following initial oviposition, later stages of maturation occurred progressively. Three levels of autogeny were distinguished within the population: mono-autogenous females that deposited 1 egg batch and were unable to initiate further oogenesis [54.4%], mono-autogenous females in which various degrees of vitellogenesis developed posterior to initial sole oviposition [40%] and bi-autogenous females [5.6%] that deposited 2 autogenous egg batches but were unable to develop any further oogenesis. The fecundity of mono-autogenous females [about 56 eggs] whether they could develop a 2nd autogenous cycle or not, was comparable to that of bi-autogenous mosquitoes in their initial egg batch [53 eggs], suggesting that ability to develop a subsequent autogenous follicular cycle is determined by factors independant of nutrient reserves accumulated during the larval stage. The 2nd egg batch of bi-autogenous females was smaller [21 eggs] than the initial batch. The total reproductive effort of bi-autogenous individuals [about 74 eggs] was superior to that of mono-autogenous females. However, bi-autogenous females laid the totality of their eggs within about 16 days, whereas the average initial gonotrophic cycle of mono-autogenous females was 6 days. It is concluded that bi-autogeny in Ae. caspius would be of little value in the population increase although it may contribute maintaining the species when the host is not available