A method for assessing chemically-induced paralysis in headless mosquito larvae

There is a growing interest in studies of mosquito physiology and toxicology due to the heightened need for controlling this group of human disease vectors. In the process of testing a group of polar compounds on mosquito muscles, a novel headless larva bioassay was developed. The heads were removed from fourth instar Aedes aegypti larvae, which permitted access of pharmacological agents to the hemocoel while maintaining larval viability. The method allowed effective quantification of the paralytic actions of water soluble compounds that could not ordinarily penetrate the mosquito larva integument and was more easily performed than injection when studying small, soft-bodied aquatic organisms.The summary of the method is:
• Heads of A. aegypti larvae were detached with two pairs of forceps, and the larvae remained responsive for at least 5 h.
• The responsiveness of the larvae was assessed by using a microscope to observe movement after the larvae were probed with an insect pin.
• Drug effects were quantified using either a binary paralysis determination (paralyzed vs. not paralyzed), or by counting movement units after probing.

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