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Figure 4.3 This scanning electron micrograph shows a biofilm of Enterobacter agglomerans and
Klebsiella species in the midgut of the apple maggot Rhagoletis pomonella . (Photo provided by C. R. Lauson.)
are most abundant in the esophageal bulb, crop, and midgut. These bacteria
are found on host plants and other substrates in the environment. It seems that
the bacteria provide usable nitrogen for R. pomonella and other tephritids by
degrading purines and purine derivatives, making them facultative symbionts.
The relationship between the Enterobacter and Klebsiella species is probably
complex. Figure 4.3 illustrates the “biofilm” of E. agglomerans and Klebsiella in
an adult R. pomonella midgut. A biofilm is a complex, structured community of
microbes attached to surfaces. Microbial biofilms function as a cooperative con-
sortium in a complex and coordinated manner ( Davey and O'Toole 2000 ). The
role of this biofilm in R. pomonella is under study ( Lauzon et al. 1998 ).
4.12.5 Symbiosis in Fungus-Growing Attine Ants
New World attine leaf-cutter ants live in the tropics, where they carry small
leaf fragments back to their nests. The leaves are used as fertilizer to cultivate
a fungus, which is their food. The fungi produce specialized structures that are
consumed by the ants. The worker ants carry out complex behaviors to maintain
the fungus gardens, as well as caring for the brood. Ant queens initiate new
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