Intraspecific variance of chaetotactic characters in the chigger mite genus Hirsutiella (Acari: Trombiculidae)

A.A. Stekolnikov

Parazitologiya, 35(1): 19-26 (2001) (In Russian, English summary).

S U M M A R Y

Numbers of scutal, coxal and sternal setae were counted in 1393 specimens of 5 Hirsutiella species. All observed chaetotactic anomalies were classified into 3 groups: 1) "rare" anomalies, such as absence of one AL, AM, coxal or sternal setae, presence of additional AL, AM, coxal or anterior sternal setae; 2) presence of 1—2 post-posterolateral scutal setae (PPL); 3) presence of additional 1—3 posterior sternal setae.

"Rare" anomalies were found in 2.8% of the specimens examined. They were observed usually in northern or alpine populations. Obviously, it is an effect of more frequent ontogenetic failures in rigorous climate conditions being out of optimum for trombiculids.

The quota of the individuals with PPL in a set of H. steineri samples varied from 16 to 74%, while in the other samples of this species the presence of the single (and not more) PPL were found very seldom, as well as in the other species examined. In the similar way, the additional posterior sternal setae were found with the frequency up to 100% in the some samples of H. steineri, H. hexasternalis and H. alpina, but in other ones they were present only in few specimens. Since in a series of cases the ratio of the number of specimens with PPL to the number of specimens without PPL, as well as the ratio of the number of specimens with fSt=2.4 to the number of specimens with fSt=2.2 is almost equal to 2, one can suppose that the variance of this characters has a genetic basis.

All samples having a high frequency of the PPL appearance or the appearance of additional posterior sternal setae were collected in the alpine zone. It is an evident example of the ecogeographical rules, which were reported previously by the author for the quantitative characters in species of the genera Neotrombicula (Stekolnikov, 1996, 1998, 1999) and Hirsutiella (Stekolnikov, 2000). It is possible that the PPL appearance is caused by the higher humidity of the climate, and the appearance of additional posterior sternal setae — by the low temperature. It is supported by the fact that the samples with high frequency of individuals having PPL are specific to damp areas of Western Caucasus, while the populations with high frequency of additional posterior sternal setae appear to be characteristic for regions with more dry climate (Daghestan, Turkey, Chelyabinsk Oblast of Russia).

The fact, that in some populations of H. steineri, the individuals having PPL are prevalent, can serve as a serious argument for the abolishment of the genera Hoffmannina Brennan et Jones, 1959 and Aboriginesia Kudryashova, 1993 distinguished from related groups only by the presence of these setae.