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United States Department of Agriculture

Agricultural Research Service

Title: Solid-to-Liquid Feeding: Story of Extra-Oral Digestion in Predaceous Arthropoda

Author
item Cohen, Allen

Submitted to: American Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 29, 1997
Publication Date: N/A

Interpretive Summary: Although predatory insects and their kin (arthropods) are regarded as major control agents of pest species and of great ecological and economic significance, their feeding mechanisms have been poorly understood. A major consequence of this misunderstanding of predator feeding has been an incorrect estimation of the potential impact that these arthropods have in agricultural systems. This study explains that the majority of predatory arthropods use a peculiar system of feeding (known as extra-oral digestion) that is based on the use of specially adapted mouthparts and special digestive enzymes all of which work to turn the insides of prey into liquid before they are ingested. Understanding this feeding mechanism will lead to the development of new models of predator impact on prey, changes in expectation about size relationships between predators and prey, numerical relationships; and it has already led to a whole, new way of presenting artificial diets to permit the technological basis for mass rearing of these beneficial organisms. The shift in paradigms about feeding should change the scientific community's perspectives about how to use predators, and it should impact the growers' and producers' understanding of utilization of predators for economic and environmentally sound crop protection.

Technical Abstract: The main feeding process in predaceous Arthropoda is extra-oral digestion, where the predator liquefies the internal contents of the prey prior to consumption. Predators use chemical and mechanical means of digesting prey before ingesting it. Scorpions, many spiders and some beetles crush the prey's exoskeleton while digesting it, leaving an amorphous wad of cuticle. Alternatively, some predators leave an intact cuticle. The process of extra-oral digestion is adaptive for predators in several ways. 1) It allows relatively small predators to utilize large prey. 2) It allows the predators to extract only the nutritious components leaving behind intractable parts such as the exoskeleton that would take up space in the gut and could cause injury to the predator's gut. 3) It allows predators to complete digestion more rapidly than would be possible with piecemeal or gulping feeding. However, there are some caveats to be aware of regarding extra-oral digestion. 1) Predators that use extra-oral digestion prefer large prey and will tend not to waste time with prey that are less than 1/10 of their own body weight. 2) These predators cannot afford to abandon their prey before they have extracted all that they can from it (i.e., prey "skimming" is not a likely feeding strategy). 3) Predators that use extra-oral digestion must recover their digestive enzymes to complete the digestive process within their gut. 4) These predators, when fed artificial diets, are much better served with solid diets that are highly concentrated with nutrients such as proteins (10-15%) and lipids (8-15%) than with liquids that are inherently very dilute (1-3% proteins and 1-3% lipids).

Last Modified: 11/27/2014
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