Asymmetry in the number of solenidia on tarsi II of Brevipalpus (Acari: Tenuipalpidae) populations from Argentina

To verify the prevailing Brevipalpus species in citrus orchards affected by leprosis in Argentina, specimens of this genus were collected mainly from ‘Valencia’ and ‘Hamlin’ varieties of sweet orange plants from experimental and commercial plantations at Bella Vista, Corrientes Province, Concordia, Entre Rios Province and Saens Peña, Chaco Province. Examinations under light microscopy and scanning electron microscopy were carried out to identify the species based on external morphological characteristics. A mixture of typical Brevipalpus obovatus Donnadieu and Brevipalpus phoenicis (Geijskes) was found, with prevalence of the former (43.7 versus 27.2%) in the 327 adult females examined. However, 29% of the total number of females examined were atypical, having one solenidion (ω”) on one of tarsi II and two (ω’ and ω”) on the other, either left or right. To investigate whether this variation was also common elsewhere, several Brevipalpus populations of the obovatus species-group from Chile (Brevipalpus chilensis Baker), Brazil (B. obovatus and B. phoenicis), Costa Rica and Paraguay (B. phoenicis in both countries) were examined. Asymmetric numbers of tarsus II solenidia were found in 11 of the 1,993 examined adult female specimens of these populations. The results suggested a relation between the high proportion of asymmetric mites in Argentina and the occurrence of a mixed population of both B. obovatus and B. phoenicis; however, present knowledge about the apparently parthenogenetic system of reproduction of these species does not support the hypothesis that asymmetric mites could be the hybrids of those species. Thus, the factor leading to high proportions of asymmetric Brevipalpus in Argentina remains unknown.