Biology Reference
In-Depth Information
at the site of the bacterial droplet. The bacteria would then be transported into the fruit and become
localized around the eggs. These bacteria were found to facilitate softening of the host tissue and
provide a nutritious environment for developing eggs and larvae. Lloyd et al. (1986) also found
that the bacteria would consistently migrate some distance ahead of a burrowing larva, presumably
digesting fruit tissue and thus making available an easier course of movement in the fruit for the
larva with a complementary availability of nutrients.
Similarly, Lauzon (1991) found that an
Enterobacter
sp. was deposited with eggs into apple
Þesh by
; however, the bacteria were deposited not via regurgitation but directly during
oviposition. While Ratner and Stoffolano (1984) suggested that fecal material may be the source
of enteric bacteria within the oviposition site, Potter (2001) visualized bacteria attached to the
internal aspect of ovipositors from
R. pomonella
spp. from this region.
Perhaps the direct deposition of bacteria through the ovipositor is typical for
R. completa
and also isolated
Enterobacter
Rhagoletis
spp. and
atypical for all tephritid pests such as
, Hendrichs
et al. (1990) found that a mix of phylloplane bacteria Ð those bacteria that typically reside on leaf
surfaces Ð did not support substantial egg production in
B. tryoni
. Also contrary to the biology of
B. tryoni
R. pomonella
.
BACTERIA IN THE LIFE HISTORY OF TEPHRITIDS:
A LINK TO NITROGEN PROVISIONING AND OTHER
METABOLIC ACTIVITIES
It makes sense that bacteria deposited into an oviposition site would provide or facilitate a
favorable environment for developing eggs and larvae in many different host fruits and nuts. Most
host fruits, for example, have dense, compact tissue that is difÝcult to penetrate and also lacks
nitrogen, a necessary component for egg and larval development. Howard et al. (1985) hypothesized
that bacteria gaining entrance into fruit tissue were likely pectinolytic. Thus, one can easily envision
that larval migration is made easier and is less energy expensive if the tissue is degraded and
softened by bacteria. The
strain isolated by Lauzon in apple tissue was conÝrmed
to possess pectinolytic capabilities (Lauzon et al., 1988).
Lack of bioavailable nitrogen in nature is a recurring theme for many living organisms on our
planet. The deposition of bacteria during oviposition could feasibly provide adequate nitrogen to
developing eggs and larvae on the basis of bacterial biomass alone. Most host fruits contain little
nitrogen, and after water, protein is the most abundant constituent of bacteria.
Drew (1988) also reported that essential amino acid content of host tissue increased in the
presence of fruit-Þy larvae. Miyazaki et al. (1968) found speciÝcally that the amino acid methionine
not present in sterile apple tissue was synthesized by a bacterium associated with
E. agglomerans
in
apple tissue and was bioavailable to larvae. Therefore, it is likely that bacteria within host fruit
serve as direct and indirect sources of nitrogen (Fitt and OÔBrien, 1985).
To create a more certain and consistent intake of nitrogen, some insects, e.g., termites, have
overcome the nitrogen dilemma by forming symbiotic relationships with dinitrogen-Ýxing micro-
organisms (Potrikus and Breznak, 1977). Few studies have been conducted to determine if nitrogen
Ýxation occurs within fruit Þy guts. Howard et al. (1985) found no evidence to suggest that this
activity occurred within the gut of
R. pomonella
R. pomonella
; however, Murphy et al. (1988) found nitrogenase
activity within
. If some tephritids possessed such a relationship, it would certainly help
those insects overcome the substantial demand for nitrogen for developing larvae and would be of
beneÝt to females who must provision enough nitrogen for developing eggs. Honeydew, a main
source of food for most adult tephritid Þies in nature, is low in nitrogen (Hagen, 1958; Neilson
and Wood, 1966; Nishida, 1980) and does not support maximum egg production.
B. tryoni
E. agglomerans
and
Klebsiella
spp. do include strains that are known to Ýx atmospheric nitrogen, and
E. agglom-
erans
have been shown to Ýx atmospheric nitrogen (C.R.
Lauzon, unpublished data). Detailed experimentation is lacking, however, for determining the
activity and extent of nitrogen Ýxation within tephritids.
strains associated with
R. pomonella
