Afrotrombicula Kolebinova and Vercammen-Grandjean, 1978

Stekolnikov, Alexandr A., 2023, A revision of the chigger genus Afrotrombicula (Acariformes: Trombiculidae), Zootaxa 5323 (1), pp. 27-55 : 28-29

Genus Afrotrombicula Kolebinova and Vercammen-Grandjean, 1978

Afrotrombicula Kolebinova and Vercammen-Grandjean, 1978: 103 ; Vercammen-Grandjean & Kolebinova 1985: 75; Stekolnikov

2018: 121. Type species. Trombicula nigeriensis Ewing, 1928 (by original designation).

Diagnosis. SIF = 7BS-B-3-3111.1(0)000; fsp = 7.7.7; fCx = 1.1.1; fSt = 2.2; fPp = B/B/NN(b)B; Ip = 750–1066; NDV = 43–110. Eyes 2 + 2, two humeral setae, numbers of setae in anterior posthumeral rows 6-6 or 6-8. Cheliceral blade with tricuspid cap and 1 weakly developed dorsal tooth; galeal setae thick, branched; palpal claw 3-pronged; palpal tarsus with 7 branched setae, nude subterminala (ζ) and basal tarsala (ω); setae of palpal femur and genu branched, dorsal and lateral palpal tibial setae nude (lateral seta with one or few small branches in two species), ventral palpal tibial seta branched. Scutum with dense small puncta (sparse puncta in A. nyongae ), subpentagonal or subhexagonal (trapezoidal in A. quadriscutala ) with rounded or straight posterior margin, sometimes concave in center, with 1 AM (absent in A. quadriscutala ), 2 AL and 2 PL setae; sensillary bases far anterior to PL; sensilla flagelliform, branched. Legs 7-segmented, 3 genualae I, mastitarsala III present or absent.

Remarks. The differences of Afrotrombicula from the close genus Neotrombicula (in the strict sense) are as follows:

1. Galeal (deutorostral) seta is heavily branched. In Neotrombicula , this seta is nude or bearing at most three rather short branches.

2. Sensillary (trichobothrial) bases are situated far anterior to the level of PL, sometimes almost equidistant from AL and PL. In Neotrombicula , they are close to the level of PL, in many species situated posterior.

3. Some variants of the shape of posterior scutal margin observed in Afrotrombicula (i.e. straight in the center and obliquely cut at edges, bilobate or with a concavity in the center) are almost unknown in Neotrombicula (a few exceptions should be specially studied).

4. Proportions of scutum being characteristic for most Afrotrombicula , with its length similar to the width, do not occur in Neotrombicula , in which the scutum is always distinctly wider than long.

5.A weakly developed dorsal tooth is probably present on the cheliceral blade of all Afrotrombicula species (see Discussion). This tooth is unknown in Neotrombicula .

Afrotrombicula differs from Hirsutiella Schluger and Vysotzkaya, 1970 and Kepkatrombicula Kudryashova and Stekolnikov, 2010 by the presence of three genualae I (vs. two), simple rows of dorsal idiosomal setae (vs. double or triple), and by the sensillary bases situated far anterior to the level of PL (vs. slightly anterior, at the level or posterior).

The numbers of non-specialized setae on leg segments in Afrotrombicula are as follows (from coxa to tarsus): leg I—1/1/1/5/4/8/22; leg II—1/1/2/4/3/6/16; leg III—1/1/2/3/6/15 (or 14 + mastitarsala). These numbers are typical for Trombiculinae ( Vercammen-Grandjean 1973). Three deviations from this rule observed in the examined specimens [ Afrotrombicula nicolei ( Taufflieb, 1958) , comb. nov. —5 setae on tibia III, instead of 6; A. rickenbachi (Taufflieb, 1965) , comb. nov. —1 seta on basifemur III, instead of 2; A. machadoi ( Taufflieb, 1962) —15 setae on tarsus II instead of 16] can be explained by a missing of some setae during examination or by an individual variation. In addition, two species, A. kenyaensis ( Goff, 1995) , comb. nov. and A. centrafricana ( Goff, 1995) , comb. nov., according to their descriptions, have 21 setae on tarsus I, instead of usual 22. A confirmation of this difference by a re-examination of the types would be desirable.

The genus was originally established with two subgenera. Afrotrombicula (Tauffliebicula) Kolebinova and Vercammen-Grandjean, 1978 , with the type species Trombicula nyongae Taufflieb and Mouchet, 1959 , differs from the nominative subgenus by the absence of mastitarsala and by the smaller and more square-like scutum. Afrotrombicula (Machadella) Taufflieb, 1965 includes one aberrant species A. quadriscutala , with missed AM, subtrapezoidal scutum, and a low number of idiosomal setae (NDV = 43–48 vs. minimum 66 in other species).