Simulium damnosum, Theobald, 1903

Hendy, Adam, Krit, Meryam, Pfarr, Kenneth, Laemmer, Christine, Witte, Jacobus De, Nwane, Philippe, Kamgno, Joseph, Nana-Djeunga, Hugues C., Boussinesq, Michel, Dujardin, Jean-Claude, Post, Rory, Colebunders, Robert, O’Neill, Sarah, Enyong, Peter & Njamnshi, Alfred K., 2021, ONCHOCERCA VOLVULUS transmission in the Mbam valley of Cameroon following 16 years of annual community-directed treatment with ivermectin, and the description of a new cytotype of SIMULIUM SQUAMOSUM, Parasites & Vectors (563) 14 (1), pp. 1-14 : 6

Identification of S. damnosum complex

Morphological and cytotaxonomic identification of S. damnosum complex larvae revealed the presence of S. squamosum s.l. and S. mengense ( Figs. 3 , 4 ), both of which have previously been reported from the area [ 11]. However, S. squamosum did not conform to descriptions of the cytotypes A, B, C, or D, known from Cameroon [ 4, 5, 7]. All specimens analysed from Nyamongo I (n = 39) and Bayomen (n = 10) contained homozygous inversions 1S-1 and 1L-3, which are generally fixed in the S. squamosum subcomplex ( Fig. 4a ) [ 32]. They also possessed a new 1L inversion from sections p34 to p39 which was homozygous and fixed within the population, and which we designate 1L-57. In addition, 16/ 17 male specimens from Nyamongo I and 3/ 3 male specimens from Bayomen possessed a sex-linked band dimorphism (3C-Sp) and a heterozygous inversion (3L/82) near the centromere of chromosome 3 ( Fig. 4b ). This was absent in all 29 females collected from both sites. The involvement of 3C in sex determination among S. squamosum is diagnostic for S. squamosum E (= type III) [ 32, 33]. Since only a small number of specimens were examined from a narrow geographic range, we propose the name S. squamosum E2 for this variant possessing inversion 1L-57.

An additional five larval specimens collected at Bayomen were identified as S. mengense based on the 1CER expanded centromere of chromosome 1 ( Fig. 4c ) and tufts of hair-like scales on the anterior dorsum of the larval thorax ( Fig. 3b ) [ 10, 15, 44]. Adult S. mengense have hairs on the subcostal wing vein [ 10, 44], but no adult flies examined from collections made between July 2016 and January 2017 (Bayomen n = 254, Nyamongo I n = 74, and Ondouano n = 77) possessed this characteristic.

Figures

Fig. 3 Head and thorax of late-instar larvae showing a S. squamosum E2, and b S.mengense with arrow pointing to tuft of hair-like scales on the anterior dorsum of the thorax

Fig. 4 Polytene chromosomes of S.squamosum E2 and S.mengense showing a chromosome 1 of S.squamosum E2 with fixed inversions 1S-1 and 1L-3, and inversion 1L-57 which was fixed in the specimens examined, b part of chromosome 3 of S.squamosum E2 male showing sex-linked band dimorphism 3C-Sp and sex-linked heterozygous inversion 3L/82 present in 19/20 male specimens examined,‘b’=blister, and c chromosome 1 of S. mengense showing expanded centromere 1CER