Avermectins, MK-933 and MK-936, for mosquito control.

Two avermectins were shown to be effective as mosquito larvicides or when fed to adult female mosquitoes in sucrose solution or in blood. Larval LC50 values of compounds MK-933 and MK-936, expressed as parts per billion, were found to be 3.94 and 2.42 for Culex pipiens, 5.85 and 2.90 for Anopheles stephensi and 23.4 and 10.4 for Aedes aegypti. When fed to adult females of An. stephensi, Ae. aegypti or Cx quinquefasciatus, MK-933 at 2.8mg active ingredient per litre in sucrose solution caused complete mortality within 60 hours. When female mosquitos engorged blood from mice injected subcutaneously 12 hours previously with MK-933 at 82 mg a.i./kg, mortality rates after 36 hours were 100% for An. stephensi, over 60% for Ae. aegypti and over 50% for Cx quinquefasciatus. Thus the systemic insecticidal effect was greater against anopheline than against culicine female mosquitoes.

[Chromosomal study of Anopheles gambiae and Anopheles arabiensis in Ouagadougou (Burkina Faso) and various neighboring villages]. / Etude chromosomisque d'Anopheles gambiae et Anopheles arabiensis à Quagadougou (Burkina Faso) et dans quelques villages voisins.

Adult females of Anopheles gambiae s.1. were collected by pyrethrum spray catch in Ouagadougou (Burkina Faso, formerly Upper Volta) and in four neighbouring villages. The collections have been carried out mostly during the 1984 rainy season. Monthly collections in some sampling sites allowed a preliminary longitudinal study. By analysis of nurse cell polytene chromosomes in adult females, An. gambiae s.str. and An. arabiensis were identified in the study area. Both species showed polymorphisms for various paracentric inversions. In all samples of An. arabiensis the frequencies of the alternative karyotypes were in Hardy-Weinberg equilibrium, suggesting panmictic conditions. Conversely, An. gambiae s.str. showed a different situation, since most of its samples had strong deficiency of certain expected heterokaryotypes. This same phenomenon was already observed in Mali, leading to the splitting of gambiae s.str. into different chromosomal forms, partially or totally reproductively isolated from each other. Each chromosomal form is characterized by different chromosomal polymorphisms. Two of these forms, Mopti and Savanna, were detected in the study area. Mopti chromosomal form is apparently associated with the presence of permanent waters (i.e. the "barrages" north of the town), while Savanna is usually found in situations where breeding places are mainly dependent from rain (e.g. in villages far from "barrages" or at the town's center).

[Cytogenetic and biometric observations on members of the Anopheles gambiae complex in Mozambique]. / Osservazioni citogenetiche e biometriche sui membri del complesso Anopheles gambiae in Mozambico.

Four species of the Anopheles gambiae complex were identified in Mozambique (East Africa) by chromosomal analysis. They were An. merus, An. gambiae s.s., An. arabiensis and An. quadriannulatus. An. merus was observed in coastal zones as well as in inner areas where the rivers are tidal and brackish and/or the soil is salty. An. gambiae s.s. is present in the central-northern regions (north of Save river) from the coast to the western mountains. On the coast it is often sympatric with An. merus. It is apparently absent south of Save river. An. arabiensis was observed in samples from the north-western hilly and mountainous areas, sympatrically with An. gambiae s.s., as well as south of Save river where often it is sympatric with An. merus. Only one specimen of An. quadriannulatus was observed. It was from a small sample collected feeding on bovid in a southern locality (Bela Vista-Maputo area). No inversion polymorphism was observed in the 446 An. merus identified. A quite low degree of inversion polymorphism was shown by both An. gambiae s.s. and An. arabiensis, involving 2Rb, 2La and 2Rb inversion systems respectively. By morphological analysis of cytogenetically identified samples of three species of the complex, number of sensilla coeloconica and palpal ratio were confirmed to be useful to distinguish An. merus from An. gambiae s.s./An. arabiensis. The overlapping areas between brackish and freshwater species become smaller when both characters are considered together, 1.5% and 3.5% being the probabilities of confusing An. merus with An. gambiae s.s. and An. arabiensis respectively.

[The Anopheles gambiae complex in Guinea Bissau]. / Il complesso Anopheles gambiae in Guinea Bissau.

Three species of the Anopheles gambiae complex were identified in Guinea Bissau (West Africa) by chromosomal analysis. They were An. melas, An. arabiensis and An. gambiae s.s. An melas was observed in coastal and insular zones of the study area as well as in areas where the rivers are tidal and brackish and bordered by mangroves. For this reason, the species occurs also in inland riverine localities such as Farim and Bissorà. An. arabiensis apparently occurs only in low numbers in a very limited inland area during the dry season. An gambiae s.s. was observed nearly everywhere in the study area. In the samples of An. melas three inversion polymorphisms occurred: one on the chromosomal arm 2R (2Rn) and two on the arm 3R (3Rc and 3Re). It was observed that the frequencies of the inverted arrangements 2Rn and 3Re were significantly higher in the islands as compared to the continental sampling localities. The An. arabiensis sample was characterized by the presence of three inversion polymorphisms: 2Ra, 2Rb and 3Ra. A very high degree of polymorphism was shown by the An. gambiae s.s. samples. Four inversion polymorphisms were observed (three on chromosomal arm 2R and one on arm 2L) with very different frequencies of the alternative arrangements in different zones of the study area. From these data it seemed possible to split the species into three populations, each of them apparently linked with a peculiar ecological situation. The first population, characterized by high frequencies of 2Rd arrangement, is present on the coastal zones and in the islands; the second one is present in the northern inland areas particularly during the dry season and it is characterized by high frequencies of 2Rb and 2La arrangements. The third population is present only in the inland zones and it is characterized by high frequencies of 2Rjb, 2Rjd and 2Rjbd arrangements.