A simple method for monitoring the respiratory rhythm in intact insects and assessing the neurotoxicity of insecticides

A simple, non-invasive method, for the monitoring of the respiratory rhythm of insects was developed. The insect was restrained and a force displacement transducer attached to one abdominal segment of the dorsal region was used to monitor the respiratory rhythm. Although the method was applied to four species of insects, the main study focused on the yellow mealworm beetle, Tenebrio molitor, due to the simplicity of the recorded respiratory rhythm. In this case, the recorded rhythmic activity represents the synchronised contraction of the dorsal abdominal muscles, driven by the respiratory central pattern generator (CPG). This non-invasive method allows prolonged and stable recording of the respiratory rhythm. The records showed a decrease in the amplitude and the duration in the rhythmic contractions to about 25 and 31% of the initial values, respectively, in the first 7 h of continuous recording. The respiratory rhythm was strongly influenced by the presence of the CO2, creating the CO2-reflex. In the beginning of the application of CO2, there was total inhibition of the respiratory rhythm and then there was a gradual increase in the tension developed by the dorsal abdominal muscles. Using this recording method, it was possible to quantify the function of the respiratory CPG, measuring the amplitude of the respiratory contractions, under normal conditions and in the presence of insecticides. The insecticides imidacloprid and deltamethrin of certain quantities were diluted in the appropriate solvent to make 50, 100 and 500 ng per insect, and were applied to the cuticle, topical application, of the immobilized insect, while recordings of the respiratory rhythm were made continuously.