Behaviors of the midge, Cricotopus (Diptera: Chironomidae) related to mutualism with Nostoc parmelioides (Cyanobacteria)

Behayiors of Cricotopus nostocicola (Wirth) related to its mutualistic interaction with Nostocparmeliotdes Kutzing were explored. The late instars and pupae probably always remaininside their Nostoc colony until emergence. Laboratory observations of 4th instar larvaeremoved from Nostoc colonies showed that only 65% of the midges were able to re-entertheir colony after 20 hours in still water, although placed less than 5 cm away, and midgelarvae could move at only 8.9 mm h 1 in still water. This suggests larvae would not be able tosurvive if they left their colony. Midge larvae attached their colonies tightly to rocks andmay use this ability to orient their colony with respect to flow. Pupation occurred at the sametime host Nostoc colonies formed hormogonia (the dispersal stage of Nostoc), and at thesame time many new, uninhabited colonies appeared. The replication of both taxa occurredsimultaneously, and may have been beneficial to both.