Biology Reference
In-Depth Information
these bacteria are important in the life history of pest tephritids and perhaps other tephritid species.
We now see a continuum with the discoveries that female Þies are particularly attracted to washed
cells of
E. agglomerans
and, to some extent,
K. pneumoniae.
The
bacteria are transmitted vertically
to the eggs via ingestion of the bacteria by female Þies, and the bacteria are present within
oviposition sites of
R. pomonella
and carried throughout all life stages
.
This scenario suggests that these bacteria are important in the life history of the Þies. The work
of Marri et al. (1996) and Marchini et al. (1997) supports this contention. They describe an anti-
bacterial substance, Ceratotoxin A produced by female
C. capitata
, that is also found on the surface
of
C. capitata
eggs. This compound exhibited killing action on
E. coli.
A substance that would
inhibit or kill
E. coli
should theoretically do the same to the closely related enterics,
E. agglomerans
and
Klebsiella
spp.; however, Marri et al. (1996) found that
E. cloacae
was not as sensitive to the
compound as
E. coli.
Therefore, it appears that some selection factors exist for these two bacterial
species within the gut and on the egg surfaces.
Our current studies include further deÝning the architecture and other metabolic activities that
occur within gut and egg bioÝlms, including using molecular techniques to ascertain if the bacteria
that compose the bioÝlm contain viable but nonculturable bacterial species. Information on the
species that comprise a bioÝlm can be just as important as the architecture of a bioÝlm in terms
of structure and function. The microbial species that inhabit bioÝlms within female Þies may be
different from those found in male Þies, and these differences could be due to nutritional or
physiological requirements. Lauzon (1991) found that female apple maggot Þies harbored a variety
of strains of
E. coli
in their alimentary canal organs contrary to the dominance of
E. coli
strains
typical of warm-blooded animal feces origin in male-Þy digestive tracts. This difference could be
due to feeding behavior, need, or a combination of the two.
MICROOGANISMS AS POTENTIAL BIOCONTROL
AGENTS OF TEPHRITIDS
Fruit Þies consume a variety of microorganisms as they feed on fecal material, rotting fruit,
and honeydew. In these natural food sources, pathogens of vertebrates and invertebrates exist. Few
accounts exist, however, describing pathogens that inÞict disease for fruit Þies, and the information
that does exist (e.g., Jacques et al., 1969; Robinson and Hooper, 1989) does not report speciÝc
causative agents and associated pathogenicity.
Serratia
marcescens
has been isolated from
C.
capitata
Weidemann and
Dacus
(
Bactrocera
)
dorsalis
Hendel Þies (Grimont and Grimont, 1978)
and from diseased or dead
R. pomonella
(Lauzon et. al., 2002).
S. marcescens
has been considered
a minor threat to insects in the past (Steinhaus, 1959); however, recent reports suggest that virulent
strains of this bacterium exist (Farrar et al., 2001; Lauzon et al., 2002).
S. marcescens
cells cannot
be considered a biocontrol agent for pest tephritids or other agricultural pests because it is a pathogen
of humans and other animals (Holt and Krieg, 1992). Products such as toxins produced by
S. marcescens
may show some promise for fruit Þy control. The use of toxins, toxic bacterial spores,
or toxin-producing bacteria, such as
Bacillus thuringiensis
, has been tested for some fruit Þy species
(Robacker et al., 1996; Navrozidis et al., 2000). Although not routinely used for fruit Þy control,
a strain of
B.
thuringiensis
isolated in Greece and applied to olives provided signiÝcant protection
against
Bactrocera oleae
infestation (Navrozidis et al., 2000).
Viruses have been found to infect some fruit Þies. Cricket Paralysis Virus was reported to be
a potential biocontrol agent for
B. oleae
, the olive fruit (Manousis and Moore, 1987). A nonoccluded
reovirus was also isolated from the olive Þy and found to be pathogen
per os
and via injection
(Anagnou-Veroniki et al., 1997). Its potential as a biocontrol agent, however, remains unclear. Most
reports of virusÏtephritid interactions describe and partially characterize viruses only. For example,
several different reoviruses have been documented to infect
C. capitata
(Plus et al., 1981a,b), but
Ýeld tests have not been implemented.
