Permethrin-induced ultrastructural changes in oocytes of Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae) semi-engorged females

Currently, the most effective method for tick control is by the use of chemical acaricides such as permethrin (active ingredient of the Advantage® Max3 acaricide, Bayer), a pyrethroid with neurotoxic action. However, data about its effect on other tick systems, such as glandular and reproductive, are still scarce. This study provides ultrastructural details of the toxic effects induced in oocytes of semi-engorged Rhipicephalus sanguineus females exposed to 206, 1031, and 2062 ppm of permethrin. The results showed that permethrin is an effective acaricide by inhibiting and/or neutralizing the tick reproductive process since oocytes of treated ticks presented major structural changes such as cytoplasm vacuolation, disruption of both membranes and cell organelles, leading to cell death. Data also showed that even in low concentrations permethrin induced changes in germ cells, making them non-viable. The defense mechanisms used by oocytes against the action of permethrin in the attempt of recovering the cellular integrity and of ensuring the viability of these cells were also described in this study.