Neurophysiological and Behavioural Effects of Deltamethrin Exposure in Digitonthophagus Gazella (coleoptera: Scarabaeinae)

The growing use of pyrethroid insecticides raises concerns regarding their sub-lethal effects on beneficial non-target insects. This study evaluates the long-term neurophysiological and behavioural consequences of deltamethrin exposure through contaminated dung in the dung beetle Digitonthophagus gazella. Adult beetles were exposed to three sublethal concentrations of the LC50 (0.275 ppm): 1/20th (LD-0.014 ppm), 1/10th (MD-0.028 ppm) and 1/5th (HD-0.05 ppm), in comparison to control, for 10, 20 and 30 days. Results revealed a dose- and time-dependent decline in tunnelling activity and brood ball production. In comparison to controls, brood ball development decreased by up to 75% after 30 days at the highest dose (HD). Neurochemical investigations further demonstrated significantly (p < 0.01) reduced levels of dopamine (DA) (12%-26%), serotonin (5-HT) (8%-27%), acetylcholinesterase (AChE) activity (8%-40%) and nitric oxide (NO) levels (66%-85%), over the course of exposure. Neurotransmitter biosynthesis genes (ddc, 5-htpdc, chat, nos) and neuropeptide signalling genes (npf, npfr, it, itr, mip) were downregulated (2.5-9-fold) in conjunction with these neurochemical changes. The findings show that chronic sublethal exposure to deltamethrin is associated with altered neurochemical and transcriptional profiles and impaired nesting behaviour in D. gazella. These findings demonstrate the sensitivity of neuroendocrine pathways to pyrethroid exposure and emphasize the significance of assessing the effects of insecticides on ecologically beneficial insects.