Biology Reference
In-Depth Information
Studies of the pea aphid,
Acyrthosiphon pisum
, show that one or more spe-
cies of facultative symbionts are present in different populations. These may
protect the wasps from entomopathogenic fungi and parasitoid wasps, modify
their tolerance to heat, modify their behavioral responses to parasitoids, and
affect host plant suitability. One facultative symbiont,
Hamiltonella defensa
,
is maternally transmitted and protects against parasitoids. Because the symbi-
ont provides protection, aphids infected with
H. defensa
“exhibited reduced
aggressiveness and escape reactions compared with uninfected aphids” (
Dion
et al. 2011
). Defensive behaviors may be costly to the aphid by reducing feeding
opportunities or reducing survival, so a reduction in such behavior could confer
a fitness advantage (
Dion et al. 2011
).
Tsuchida et al. (2010)
report that a facultative symbiont (
Rickettsiella
) found
in some populations changes the aphid's body color from red to green by
increasing the amounts of blue-green polycyclic quinones, which could reduce
predation by lady beetles.
Serratia symbiotica
is another secondary symbiont of
pea aphids, providing defense against environmental heat stress and is related
to free-living bacteria that can be pathogens to animals (
Burke and Moran
2011
). Although
S. symbiotica
is considered to be a relatively recently evolved
symbiont, its genome has characteristics of older symbionts, including elevated
rates of evolution and reduction in genome size. It seems to be dependent
upon its host for some essential nutrients (
Burke and Moran 2011
).
Simon et al.
(2011)
found that a
Spiroplasma
infection of some populations of the pea aphid
affected the time at which females first reproduced, their total fecundity, lon-
gevity, and the proportions of asexual females and males. Male killing caused
by
Spiroplasma
occurred in some pea aphid populations, caused by mortality at
early nymphal stages of the sexual phase. Another endosymbiont,
Regiella insec-
ticola
, is found in the pea aphid (and other aphids) (
Oliver et al. 2010
).
Tsuchida
et al. (2011)
showed that
R. insecticola
allows the pea aphid to attack clover and
reproduce at a higher rate on clover, broadening the host-plant range of the
pea aphid in Japan. Experimental transfer of
Regiella
from the pea aphid to the
vetch aphid (
Megoura criassicauda
) allowed the vetch aphid to grow and repro-
duce on clover, a host that was not used previously.
4.12.8 Tsetse Fly Symbionts
Tsetse flies (Glossinidae) are vectors of African sleeping sickness disease in
humans and animals. Microorganisms associated with these flies, which are
blood feeders, are responsible for nutrients not found in their restricted diet.
Different microorganisms have been found in the midgut, hemolymph, fat body,
and ovaries. Until molecular techniques were used, their taxonomic status was
