Immunosuppressive effects of the limonoid azadirachtin, insights on a nongenotoxic stress botanical, in flesh flies.

The tetranortriterpenoid azadirachtin (Aza) is a well-known insect growth disruptor of plant origin. Although its actions on insects have been extensively studied; fragmentary reports are available from the immunological point of view. Therefore, in the present study, total (THC) and differential hemocyte counts (DHC), nodulation, phenoloxidase (PO) activity, immune-reactive lysozymes and inducible nitric oxide (NO) were assessed, as measures of immune responses, in Sarcophaga argyrostoma 3 instars challenged individually with M. luteus or Aza, or in combination with both compared to the control larvae. THC was significantly declined after 12 h and 24 h of treatment with Aza. DHC varied considerably; in particular, plasmatocytes were significantly decreased after 36 h and 48 h of treatment with Aza; whereas granulocytes were significantly increased. Nodulation was significantly increased with the increase of time after all treatments. Challenging with M. luteus significantly increased the activity of PO in hemocytes and plasma; whereas such activity was significantly decreased after treatment with Aza or combined Aza and M. luteus. Treatment with Aza or M. luteus alone or in couple significantly increased lysozyme activity of fat body, hemocytes and plasma. However, challenging with M. luteus significantly increased NO concentration in the same tissues. A hypothetical model of Aza as a potential mutagen is presented. However, no genotoxic effect was observed through tracking apoptosis-associated changes in Aza-treated hemocytes via flow cytometry-based apoptosis detection. Our study suggests that the integration of Aza, as an eco-friendly pesticide, with bacterial biopesticides may be a successful approach for controlling insect pests.