Diplopods are ecologically important soil organisms that may also act as economically
damaging species in urban and rural areas when their populations undergo outbreaks. They
are, therefore, sometimes targetedfor agrochemicals action. Thus, some insecticides (e.g.,
deltamethrin) have been applied in order to control diplopods home invasions and crop
attacks. Deltamethrin is characterized by its action on the nervous system; however, its effects
on diplopods have yet to be analyzed. Additionally, there are few studies on the morphology
and structure of the nervous system of diplopods. The present study aimed to elucidate the
anatomy and morphology of the nervous system of the species Gymnostreptus olivaceus
through direct observation during dissection under a stereomicroscope and by histological,
histochemical, and cytochemical analyses. It was observed that the nervous system of the
species consists of a brain and ventral nerve cord that are both wrapped by a perineurium, a
neural lamella, and, more externally, by an external cell sheath that was first described in
Diplopoda. Histological details were described for each of this species’ nervous system
structures. Furthermore, a commercial formulation of deltamethrin was applied to evaluate the
effectiveness of the popular use of this insecticide to combat diplopods infestations. In order
to observe neurotoxic effects caused by the insecticide, a synapsin labeling was used and
assessed by confocal microscopy. Four concentrations of deltamethrin were applied topically
to G. olivaceus individuals; the lowest concentration was based on the manufacturer's
recommendations for controlling other arthropods, while the other concentrations correspond
to one fifth of the LD50 previously established for the species, the LD50 itself, and twice the
LD50. Death numbers were evaluated and synapsin levels were assessed in the brain at 12, 24
and 48 hours after insecticide treatment. The insecticide was lethal only at the two higher
concentrations employed, in which no change was observed in neurotransmission. On the
other hand, the field concentration caused no mortality, but did produce significant changes in
synapsin levels. These findings cast doubt on the viability of this chemical control approach
against diplopods and suggest that millipedes may be employed for contaminants
neurotoxicity assessment, however synapsin should not be used alone in the evaluation of
such effects.
