Body-weight gains in Blaberus craniifer cockroaches and the intensity of their infection with gregarines and nematodes

Intestinal parasites are considered to be able to hinder growth of the host animals, reducing the extent of food metabolism, damaging the intestines' integrity by filling it with products of their metabolism. However, a long co-evolution can mitigate the negative impact of a parasite on the host organism. To study how parasites - nematodes Cranifera cranifera (Chitwood, 1932) Kloss, 1960 (Oxyurida, Thelastomatidae) and gregarines Protomagalhaensia granulosae Peregrine, 1970 and Blabericola cubensis (Peregrine, 1970) Clopton, 2009 (Eugregarinorida, Blabericolidae) - afffect the growth rates of cockroaches, we performed an experiment on 200 larvae of Blaberus craniifer Burmeister, 1838 (Blattodea, Blaberidae), varying in weight and age. We monitored changes in their body weight, intensity of food consumption, and after the experiment we counted gregarines in the midgut and nematodes in the hindgut. As a result, we found that 100% of the cockroaches were infected with two species of gregarines and one species of nematodes. The intestines of small cockroach larvae (weighing 300-400 mg) contained 16-18 specimens of gregarines on average. Large larvae had a weak tendency towards increase in the intensity of gregarine infestation. Similarly, there occurred changes in the intensity of nematode invasion: young larvae were infected on average by 8-10 specimens of nematodes and large larvae had an average of 12-14 nematodes. At the level of tendency, nematodes were observed to enhance the cockroaches' growth rates following increase in intensity of the parasitic infection. We found that the two groups of parasites had no effect on one another: the number of gregarines had no effect on the number of specimens of nematodes and vice-versa, the number of nematodes had no effect on the number of gregarine specimens. Perhaps, this is related to different localizations of the parasites: gregarines for most of their life feed in the small intestine, while nematodes feed in the large intestine. Therefore, growth rates of the cockroaches in our experiment have not changed due to the parasites. This indicates minimization of negative effects of gregarines in the midgut and nematodes in the hindgut on the host's life cycle, developed over long co-evolution.