Bacterial symbiotes from the caeca of certain Heteroptera

Abstract does not appear. First page follows.

Introduction

Since the early years of the nineteenth century it has been known (e.g., see (Dufour, 1833)4 that the posterior end of the midgut in certain groups of Heteroptera is characterized by the presence of saclike appendages opening into it. These evaginations, called “gastric caeca” or simply “caeca,” apparently serve a purpose different from that of the so-called gastric caeca of the Acrididae, and they appear almost always to contain specific bacteria. The bacteria from different Heteroptera may vary in their morphology, but they are relatively constant for a given insect species. The caeca themselves also vary a great deal in their morphology according to species, showing simple to complex arrangements, and apparently reflect basic phylogenetic relationships.

Although there have been a number of studies (e.g., those by (Forbes, 1892); (Glasgow, 1914); (Kuskop, 1924); (Rosenkranz, 1939); (Schneider, 1940) very little has been accomplished toward revealing the nature, kind, or function of the caecal bacteria. Of their function we are most ignorant; certainly it can be said that the role of the bacteria, and their relation to the host insect, are not clearly understood. (Glasgow (1914)) assumed that the caecal bacteria not only inhibited the development of “foreign” or adventitious bacteria but excluded them altogether. Others (e.g., (Kuskop, 1924) have thought they might play a nutritional role.

In size and shape, the bacteria, as they occur in different species of Heteroptera, range from small coccuslike bacilli to large vermiform or spirochete-like forms. Attempts to cultivate the bacteria on ordinary bacteriological media have not met with much success. (Glasgow (1914)) reported the cultivation of the symbiote from the caeca of the squash bug, Anasa tristis (De Geer), and of certain other coreids, in nutrient broth and agar; and Steinhaus