Biology Reference
In-Depth Information
GENERAL TERMS FOR DESCRIBING
MICROBE-TEPHRITID INTERACTIONS
Early studies on bacteriaÏtephritid interactions often described any bacteria isolated from life
stages as symbionts. This description of the association between bacteria and fruit Þies could be
Þawed because the bacteria may have been contaminants or not necessarily Ñliving togetherÒ with
the insects. Drew and Lloyd (1991) were both correct and responsible when they stated that the use
of the terms symbionts and symbiosis in early studies implied that bacteria and fruit Þies were engaged
in Ñmutually obligatory relationships which often were not demonstrated.Ò This assumption has been
one of the biggest obstacles to understanding completely relationships between bacteria and tephritids.
Therefore, before providing a clear description of bacteriaÏtephritid interactions we must avoid the
tendency to make assumptions and acknowledge, at a minimum, four caveats. First, symbiosis can
be deÝned broadly and simply as Ñliving togetherÒ or be tightly and narrowly deÝned as Ñan obligatory
relationship,Ò with several variations of these two descriptions in between, such as commensalism.
Therefore, the term symbiosis should be strictly deÝned in all cases. Second, bacterial relationships
can be associated as (1) external extracellular, (2) internal extracellular, or (3) internal intracellular
(Jones, 1984). Thus, bacteria can be and are associated with tephritids in a variety of ways and may
have a variety of effects on the insect Ð negative, positive, or neutral. The third caveat is that members
of the family Tephritidae display behaviors and use host plants in ways that are not consistent for all
tephritid species. Therefore, an association for one species may not be true for all members of the
Tephritidae or even true for species within a single genus. The fourth caveat is that the life history of
tephritids includes aspects of plant, soil, vertebrate, and invertebrate microbiology. More than 10 years
have passed since the last compilation of work was presented on tephritidÏmicrobe interactions (the
reader is referred to Barbosa et al., 1991). This chapter serves to expand on that work and thus present
more demonstrative and deÝnitive accounts of bacteriaÏtephritid associations. A few accounts of other
microbeÏtephritid interactions are brieÞy mentioned.
BACKGROUND: EXPOSURE, ACQUISITION,
AND TRANSMISSION
The Ýrst published accounts of bacterial associations for tephritids began in the early 1900s
when Petri (1909) described
Pseudomonas savastanoi
, a bacterial symbiont of the olive Þy,
Dacus
oleae
(Gmelin). Petri found that the extracellular bacterium inhabited the esophageal diverticulum
and an invagination near the distal end of the female ovipositor. Petri speculated that during
oviposition the eggs would be coated with bacteria that would eventually enter the micropyle of
the eggs and remain there until the bacteria eventually became established within the larval midgut.
Though Petri noted that the bacterium was transmitted from one generation to the next, no clear
mechanism of this transmission was described, and no role of the bacterium was elucidated.
While a mechanism of transmission remains undeÝned to date, a possible role for a bacterial
species emerged when, in laboratory studies using
D.
oleae
, Hagen (1966) found that
P. savastanoi
hydrolyzed protein in olive Þesh and inferred that the bacteria synthesized or provided amino acids
necessary for larval development. ArtiÝcial larval diet containing antibiotics inhibited larval devel-
opment (Tzanakakis et al., 1983), presumably because important bacteria were inhibited or elimi-
nated; however, it was not determined that the effects were truly due to any lack of important
bacteria. It is possible that the antibiotic was toxic to the larvae and exerted some negative effects
on insect development, or perhaps the antibiotic interfered with the nutritive quality of larval diet.
These questions can and should be addressed for bacteria associated with the olive Þy, despite the
Ýndings of Luthy et al. (1983), who suggested that the reported symbiont of
D. oleae
was a case
of bacterial misidentiÝcation. Regardless,
is a serious economic pest and affects olive
production worldwide; in addition, enough evidence exists to suggest that bacteria are important
in the life history of these Þies.
D. oleae
