Biology of the Midge Cricotopus Inhabiting the Alga Nostoc in California

MASTERS THESIS: Midge larvae living in the blue-green alga, Nostoc parmelioides, were reared and found to consist of two unknown species, which were described for this paper by W.W. Wirth of the U.S. National Museum. The chironomids, Cricotopus nostocicoa and C. fuscatus, play an interesting and important role in the life cycle of this alga Measurements of head capsule widths of the mixed populations revealed that there were four larval instars present, each having a distinctive color pattern. The characteristics of the various instars are described and their relationships to the alga are discussed .The larva lives in a characteristically shaped passageway which it creates during the process of feeding (on the algal pad) . Although such a niche is of protective value to the chironomid larva, it by no means offers complete safety, since a parasitic nematode plays an important role in larval mortality. For the chironomid the main advantages are shelter, food and protection from most enemies. Nostoc gains from the fact that the larva is able to cement the alga to a firm substratum whenever it is dislodged. The chironomid s presence may also enhance the reproductive methods of the alga. A direct mutual affect may be involved in the exchange of metabolic wastes.