The tube-like heart (green) extends along the body, interlinked with the diamond-shaped alary muscles (also green) and surrounded by pericardial cells (red). Blue depicts cell nuclei.
The individual species of the complex are morphologically difficult to distinguish from each other, although it is possible for larvae and adult females. The species exhibit different behavioural traits. For example, Anopheles quadriannulatus is both a saltwater and mineralwater species. A. melas and A. merus are saltwater species, while the remainder are freshwater species.[7]Anopheles quadriannulatus generally takes its blood meal from animals (zoophilic), whereas Anopheles gambiae sensu stricto generally feeds on humans, i.e. is considered anthropophilic.[citation needed]
Identification to the individual species level using the molecular methods of Scott et al. (1993)[8] can have important implications in subsequent control measures.
Anopheles gambiae in the strict sense
An. gambiae sensu stricto (s.s.) has been discovered to be currently in a state of diverging into two different species—the Mopti (M) and Savannah (S) strains—though as of 2007, the two strains are still considered to be a single species.[9][10]
A mechanism of species recognition using the sound emitted by the wings and identified by Johnston's organ was proposed in 2010,[11] however this mechanism has never been confirmed since, and the overall mechanism theory through "harmonic convergence" has been challenged.[12][13]
The genetics and genomics of sex chromosomes have been discovered and studied by Windbichler et al., 2007 and Galizi et al., 2014 (a Physarum polycephalumhoming endonuclease which destroys X chromosomes), Windbichler et al., 2008 and Hammond et al., 2016 (methods to reduce the female population), Windbichler et al., 2011 (trans from yeast), Bernardini et al., 2014 (a method to increase the male population), Kyrou et al., 2018 (a female necessary exon and a homing endonuclease to drive it), Taxiarchi et al., 2019 (sex chromosome dynamics in general) and Simoni et al., 2020 (an X chromosome destroying site specific nuclease).[15] See § Gene drive below for their applications.
An. gambiae has a high degree of polymorphism. This is especially true in the cytochrome P450s, Wilding et al., 2009 finding 1 single nucleotide polymorphism (SNP)/26 base pairs. This species has the highest amount of polymorphism in the CYPs of any insect known, much tending to be found in "scaffolds" that are found only in particular subpopulations. These are termed "dual haplotype regions" by Holt et al., 2002 who sequenced the PEST strain.[16]: 241
Parasites/bioinsecticides and chemical insecticides synergistically reduce fitness. Saddler et al., 2015 finds even An. gambiae with knockdown resistance (kdr) are more susceptible to DDT if they are first infected with Plasmodium berghei[20][21] and Farenhorst et al., 2009 the same for Metarhizium robertsii or Beauveria bassiana.[20] This is probably due to an effect found by Félix et al., 2010 and Stevenson et al., 2011: An. gambiae alters various activities – especially CYP6M2 – in response to P. berghei invasion. CYP6M2 is known to somehow produce pyrethroid resistance, and pyrethroids and DDT share a mechanism of action.[21]
Gene drive
Research relevant to the development of gene drive controls of An. gambiae have been performed by Windbichler et al., 2007, Windbichler et al., 2008, Windbichler et al., 2011, Bernardini et al., 2014, Galizi et al., 2014, Hammond et al., 2016, Kyrou et al., 2018, Taxiarchi et al., 2019 and Simoni et al., 2020.[15] For specific genes involved see § Genome above. These can all be used in pest control because they induce infertility.[15]
Fecundity
Fecundity of An. gambiae depends on the detoxification of reactive oxygen species (ROS) by catalase.[23] Reduction in catalase activity significantly reduces reproductive output of female mosquitoes, indicating that catalase plays a central role in protecting oocytes and early embryos from ROS damage.[23]
Historical note
An. gambiae invaded northeastern Brazil in 1930, which led to a malaria epidemic in 1938/1939.[24] The Brazilian government assisted by the Rockefeller Foundation in a programme spearheaded by Fred Soper eradicated these mosquitoes from this area. This effort was modeled on the earlier success in eradication of Aedes aegypti as part of the yellow fever control program. The exact species involved in this epidemic has been identified as An. arabiensis.[25]
^Giles, G. M. (1902). A handbook of the gnats or mosquitoes giving the anatomy and life history of the Culicidae together with descriptions of all species noticed up to the present date. London, United Kingdom: John Bale, Sons & Danielsson.
