Sunday, September 8, 2019

Tiny Ninjas, Big Bites (A Guest Post)

By Alexis Brauner

Venom isn’t just a weapon for snakes and spiders.

A smaller, more dangerous insect is in existence and falls into the realm of venomous creatures: the assassin bug. This little critter is part of a scientific family called Reduviidae, a group where all the members share the same characteristic of being an ambush predatory bug. They prey on invertebrates (animals that don’t have a spine), such as crickets and mealworms, by injecting venom into them.

An assasin bug. Source: Fir0002/Flagstaffotos at Wikimedia Commons.

Assassin bugs are believed to have two versions of venom – one for feeding and one for defense. Both types of venom are made up of more than 100 proteins, but what is unique about it is its ability to paralyze and liquify the inside of the prey. That’s right… liquify. The tissues of the prey turn into a jello-like substance that the assassin bug can then suck through a long tube on its mouth called the proboscis.

How is the venom able to do that?

First, let’s peek at the mechanisms that work to carry the venom through the body of the assassin bug and into its meal.

The venom apparatus of an assassin bug is made up of three main parts: secretory glands, a muscle-driven pump, and a venom channel. The three secretory glands (the anterior main gland, posterior main gland, and accessory gland) are in the thorax and abdomen of the assassin bug. These separate glands release a specific form of assassin bug venom depending on what situation the bug is facing. For example, the anterior main gland releases a form of venom that does not paralyze prey but is thought to be used as a defense mechanism, while the posterior main gland releases the deadly form of venom.

The venom apparatus of an assassin bug. Source: Walker, et. al, 2018, modified by Alexis Brauner

Once released, the venom then makes its way to a muscle-driven pump within the head of the bug. The pump fills with the available venom when the muscle contracts and is released once the muscle relaxes. Think of the venom pump as a clothes pin: when you push on the prongs, the pin opens, and you can put things in it to hold; once you let go of the prongs, the mouth of the pin closes, but now the prong end is open. In this example, your fingers are the muscle and the clothes pin is the pump with one end open at a time. The muscle relaxation releases the venom into the venom channel in the interlocking maxillary stylets (also known as the fangs) of the assassin bug. And then…

BOOM!

Venom is in the food or the foe.

And if it’s in the food, then the tissues of the prey turn into liquid. This liquification phenomenon is caused by enzymes in assassin bug venom called proteases. All enzymes catalyze, or speed up, chemical reactions; however, proteases are specialized enzymes that catalyze the destruction of proteins. This means that the assassin bug venom goes into the prey and the proteases are like Pac-Men with razor sharp teeth that grind up the primarily protein tissue at such a lightning fast speed that, within seconds, the prey is juice!

Scientists continue to research assassin bug venom to learn more about its components, but one thing is for sure: The extraordinary liquid weapon housed in such a small insect is why assassin bugs are tiny ninjas with big bites.


To learn more:

Walker, A., Madio, B., Jin, J., Undheim, E., Fry, B., King, G. (2017). Melt With This Kiss: Paralyzing and Liquefying Venom of The Assassin Bug Pristhesancus plagipennis (Hemiptera: Reduviidae). Mol Cell Proteomics, 16 (4), 552-566. DOI: 10.1074/mcp.M116.063321.

Walker, A., Mayhew, M., Jin, J., Herzig, V., Undheim, E., Sombke, A., Fry, B., Meritt, D., King, F. (2018). The assassin bug Pristhesancus plagipennis produces two distinct venoms in separate gland lumens. Nat Commun, 9, 755. DOI: 10.1038/s41467-018-03091-5

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