gene revealed that these bacteria are closely
related to Wolbachia from Leptopilina australis
(Belizin) but not to those in E. formosa(van
Meer et al., 1999). Wolbachiaspp. were also
detected in an Australian parthenogenic
form of Eretmocerus mundus(De Barro and
Hart, 2001). Parasitoids treated with the
antibiotic rifampicin produced males that
were partially functional, as they produced
sperm, copulated with females and insemi-
nated them. However, no sexual line could
be established. For each of the three genera-
tions following antibiotic treatment, infected
females produced more progeny than cured
females, due to a greater egg mortality in the
cured line (De Barro and Hart, 2001). Most
descendants of cured females were free of
detectable Wolbachiainfection.
UNIDENTIFIED DISEASE.Varying numbers of lab-
oratory-reared E. mundus Mercet females
were found to be sterile (Gerling and Fried,
1997). At a lower rate, sterility also occurs in
field populations. Sterility in E. mundus is
significantly correlated with crowding of
female parasitoids during oviposition and is
variable among laboratory populations
(Gerling and Fried, 1997). Sterile females
show pronounced behavioural changes and
appear more restless. Sterility is thought to
be induced by an unknown pathogen
(Gerling and Fried, 1997).
Lysiphlebus(Aphidiidae): parasitoids
of aphidsBACTERIA.Wolbachia-induced thelytoky has
been reported in Lysiphlebus cardui
(Marshall), Lysiphlebus confusus (Tremblay
and Eady) andLysiphlebus fabarumMarshall
(cited by Stary ́, 1999). Thelytokous popula-
tions of these three species consist almost
exclusively of females, although males are
occasionally produced. Arrhenotokous and
thelytokous populations coexist in the same
localized areas (Stary ́, 1999). However, the
distribution of thelytokous populations is
restricted to the West Palaearctic species of
Lysiphlebus. Wolbachiaspp. have not been
detected in Lysiphlebuspopulations of North
America, despite an extensive study of this
group (cited by Stary ́, 1999). Thelytokous vir-
gin females of the three Lysiphlebusspecies
display two peculiar behavioural features.
First, they refuse the mating attempts of
biparental males and, second, they form
aggregations whereby they display aberrant
oviposition behaviour by attempting to
oviposit in each other. The thelytokous trait
is maternally transmitted (Stary ́, 1999).Muscidifurax(Pteromalidae): parasitoids of
flies
BACTERIA.Wolbachia endosymbionts present
in a parthenogenetic strain of Muscidifurax
uniraptorKogan and Legner were not found
in the closely related sexual species M. raptor
(Stouthamer et al., 1993). Sequence analysis
of the 16S rDNA revealed that Wolbachiaspp.
of M. uniraptorare most closely related to
Wolbachia spp. that induce cytoplasmic
incompatibility in different Nasonia species
(Stouthamer et al., 1993). Wolbachiadensities
are reduced when adult females are treated
with the antibiotic rifampicin, resulting in an
increase in the proportion of male offspring.
Both Wolbachia density and the number of
male offspring are dependent on antibiotic
dose (Zchori-Fein et al., 2000). Results indi-
cate that Wolbachiaspp. have no effect on the
fecundity, longevity or reproductive rate of
M. uniraptor(Zchori-Fein et al., 2000). Two
additional studies have failed to detect any
negative effects of Wolbachia on host fitness
(Stouthamer et al., 1994; Horjus and
Stouthamer, 1995). These findings are in
accordance with the hypothesis that a nega-
tive effect of Wolbachiaon host fitness is not
expected in species where the symbiont
infection has gone to fixation, as in M. uni-
raptor(Stouthamer et al., 1994). Gottlieb and
Zchori-Fein (2001) found three reproductive
barriers between antibiotic-induced males
and conspecific females of M. uniraptor:
males do not produce mature sperm, females
are reluctant to mate and a major muscle is
absent from the spermatheca. These findings
support the hypothesis that thelytokous
reproduction is irreversible in M. uniraptor.PROTOZOA.Microsporidia are common
pathogens of pteromalid parasitoids associ-
ated with livestock and poultry houses,Pathogens of Natural Enemies and Pollinators 151