BY DR. JOSE PALU-AY DACUDAO
QUICK. What is the commonality among praying mantises, cockroaches, and termites?
They all have the same egg casing, called the ootheca. This casing protects their eggs, and is only found among these three insects. In the case of termites, it has been determined that they form their ootheca internally, so you don’t actually see termite egg casings exposed in the environment, unlike those of cockroaches and mantids. (I sometimes find dark brown cockroaches’ egg casings in the drawer under my kitchen sink and mantid casings on plants.)
Aside from that, they also share a characteristic ‘skull’ with a unique (to them) internal opening.
Because of the above, they have been traditionally classified under the clade dictyoptera.
Praying mantises aren’t pests. The other two frequently are. And what makes cockroaches and termites pests? They both can eat paper. In the case of termites, even wood is included in their diet.
In the 1940s, it was found that termites and the clade of wood-eating cockroaches called cryptocercus share certain flagellates, protozoans with hair-like protrusions for mobility. (If you open up a rotting log, you can sometimes see wood-eating cockroaches scampering out.) These protozoans can degrade cellulose, the main component of paper and wood. These microbes are what makes termites to be such pests in wooden houses.
Moreover, cockroaches often congregate together.
Thus, for about 70 years, termites and cockroaches were regarded as close relatives. It has been generally assumed that they form separate sister orders, the isoptera (termites) and the blattodea (cockroaches) under the dictyoptera. Biology students until the early 2000s are taught this. But the situation was still quite unclear because of small sample sizes.
Then in 2007, the most extensive phylogenetic study, by Inward et al, on the Dictyoptera, came out. It included 15 mantid families, all six cockroach families, 22 of the 29 cockroach subfamilies, and all termite families and subfamilies. Two mitochondrial and three nuclear genes were utilized.
To make matters brief, the clade of termites was determined to be deeply nested among cockroaches.
Ha! That means that termites ARE cockroaches.
The authors of the study hypothesize that a group among ancient wood-eating cockroaches began to transmit their gut microbes to their offspring by coprophagy, meaning their offspring ate their parents’ feces. In order to more effectively transmit a stable set of these cellulose-digesting protozoans, these cockroaches evolved as follows. One, they began to get more and more gregarious, forming colonies. Two, they began to care for their young for extended periods of time within the colonies, in order to be certain that their gut microbes got properly transmitted. Ootheca eventually were lost because the protection afforded by these egg casings is not needed inside a wooden nest. The colony members took to doing different tasks in order to produce more offspring and support them. Thus, eventually a caste system evolved.
It is not only the Hymenopterans (wasps, bees, ants) among insects that have evolved eusociality, but cockroaches as well. Termites are eusocial cockroaches that live in colonies with caste systems in order to better produce and care for offspring./PN
