The Sonoran Desert Turtle Ant, Cephalotes rohwer, maintains bacteria in large numbers in the lumen of the midgut and hindgut. The type of bacteria is restricted to 16-20 strains that are transmitted to newly emerged adult workers shortly after they molt. These bacteria are hypothesized to have a symbiotic nutritional role. The worker ants forage on a variety of foods that contain micro-organisms. However, the midgut and hindgut only contain the transmitted bacteria and never bacteria present in food. How are those bacteria excluded from the midgut?
A group of scientists* investigated the proventriculum of worker ants and found that a filter is formed in the proventriculus. Newly emerged adults acquire symbiont bacteria through trophallaxis. After those bacteria pass to the midgut and hindgut, the filter forms in the proventriculus that is capable of passing liquids, but excludes bacteria and particles smaller than 0.2 microns. The filter is formed by a mucous secretion that fits in the channel between the crop and midgut.
The filter not only excludes bacteria but also food particles. How do the ants digest food? The foraging workers regurgitate food from their crop to feed larvae. The larvae larvae lack the filter and food particles readily pass into the larval midguts where it is digested.
*Michele Caroline Lanan, Pedro Augusto Pos Rodrigues, Al Agellon, Patricia Jansma & Diana Esther Wheeler. A bacterial filter protects and structures the gut microbiome of an insect. International Society for Microbial Ecology. 2016/02/12/online.