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Two new species of chigger mites (Acari: Trombiculidae) close to Neotrombicula minuta, application of nonlinear multivariate statistics

A.A. Stekolnikov

Acarina. Russian Journal of Acarology, 16 (1): 21-29 (2008).


Two new species of chigger mites, Neotrombicula urartensis sp. n. from rodents and birds and N. kubanensis sp. n. from rodents, are described from Caucasus.

Neotrombicula urartensis sp. n. differs from N. scrupulosa Kudryashova, 1993 in having much more numerous ventral and caudal idiosomal setae (larger VC, VS, and NDV), lesser number of dorsal idiosomal setae in rows 1—4 (D1-4), lesser m-t, and longer AM. There are usually 6 setae in 1st row (13 of 17 specimens measured), while N. scrupulosa has more frequently 7—11 setae in 1st row (only 28 specimens of 244, i.e. 11.5%, have 6 setae in 1st row). This material was previously identified as N. corvi Kolebinova, 1971 (Stekolnikov, 1995), but according to new data N. corvi is rather similar to N. scrupulosa.

N. kubanensis sp. n. clearly differs from all other species of the minuta group in having much longer AM reaching posterior scutal margin (AM = 45—49 versus 25—44). The new species resembles N. agriotricha Stekolnikov, 1994 in having long barbs on scutal and idiosomal setae and similar arrangement of dorsal idiosomal setae, but differs from it (except for the longer AM) in having a nude lateral palpal tibial seta versus branched, smaller scutum (AW = 64—68, PW = 81—86, PSB = 22—26, SD = 46—55, AP = 22—26, versus 68—71, 86—92, 27—32, 54—60, and 27—31, respectively), the much shorter legs (Ip = 702—776 and TaIII = 58—66 versus 844—900 and 76—83), and the lesser number of idiosomal setae (VS = 21—29 and NDV = 47—62 versus 28—33 and 59—67).

Morphological discontinuity of Neotrombicula urartensis and N. scrupulosa was demonstrated using logistic regression analysis. Logistic regression analysis yielded the following diagnostic equation:

P(N. urartensis) = Exp(–56.237 + 1.268*VC)/(1 + Exp(–56.237 + 1.268*VC)).

If P > 0.5, the new specimen should be identified as N. urartensis, otherwise it is predicted to be N. scrupulosa. Solution of this equation give boundary value of VC between 44 and 45. Thus, according to the obtained diagnostic rule, N. urartensis should have VC = 45 (P = 0.69) or more, while in N. scrupulosa VC = 44 (P = 0.39) or less.

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