Associate Certified Entomologist (ACE) Practice Exam

How do macrocyclic lactones typically affect insect physiology?

1. By enhancing energy production

2. By blocking GABA channels

3. By disrupting endocrine signals

4. By increasing muscle contraction

The correct answer is: By blocking GABA channels

Macrocyclic lactones are a class of compounds that primarily target the nervous system of insects. They work by binding to glutamate-gated chloride channels and GABA (gamma-aminobutyric acid) receptors in the neurons of the insect, leading to an influx of chloride ions into the cell. This process results in hyperpolarization of the neurons, effectively inhibiting neuronal excitability. The result of this action is paralysis of the insect, as the normal transmission of nerve impulses is disrupted, preventing movements and critical physiological functions. This mechanism of action is particularly effective against a variety of parasitic and pest insects, making macrocyclic lactones valuable in agricultural and veterinary entomology. The disruption of GABA channel activity stands out as the key physiological effect of these compounds. By targeting the neurophysiological pathways, macrocyclic lactones provide a powerful means to control insect populations. The other choices do not accurately reflect the primary mode of action of macrocyclic lactones in insect physiology. Enhancing energy production, disrupting endocrine signals, or increasing muscle contraction do not align with their established biochemical interactions and effects on the insect nervous system.