that are heavily infected with N. polyvora
produce few progeny. The ovaries of infected
females contain eggs with many
microsporidian spores. These eggs are inca-
pable of developing within P. brassicae; how-
ever, they are able to infect the host with
microsporidia (Issi and Maslennikova, 1966).
The microsporidium N. mesnilialso infects C.
glomerataand its host, P. brassicae. Infected
parasitoid larvae may die prematurely if the
host is heavily infected (Tanada, 1955;
Hostounsky ́, 1970).
The microsporidium Nosema bordati is
highly pathogenic to Cotesia flavipesCameron
and its host, the cereal stem borer Chilo
partellus(Swinhoe). High parasitoid mortal-
ity is observed in all stages of infected C.
flavipes, and dead larvae and pupae contain
high numbers of spores. N. bordatiis trans-
mitted transovarially (Kfir and Walters,
1996). It multiplies in all stages of C. flavipes
and may be horizontally transmitted by
infected parasitoids (Bordat et al., 1994).
Encarsia(Aphelinidae): parasitoids of mainly
whitefliesBACTERIA.All known populations of Encarsia
formosa Gahan are parthenogenetic (Zchori-
Fein et al., 1992). However, male production
can be induced by exposing infected females
to high temperatures (31°C) for two or more
generations (Kajita, 1993) or by treating them
with certain antibiotics (Zchori-Fein et al.,
1994). Resulting male progeny produce
sperm and may mate but insemination of
females does not occur (Zchori-Fein et al.,
1992). It is possible that E. formosa has been
parthenogenetic for such a long time that
behavioural, physical and/or mechanical
prezygotic barriers exist in either males or
females that prevent fertilization (Zchori-
Fein et al., 1992). Thelytoky (parthenogenetic
reproduction in which only females are pro-
duced) in E. formosais mediated by Wolbachia
symbionts (van Meer et al., 1995). Sequence
analysis of 16S rDNA reveals that the sym-
biont of E. formosa is closely related to
Wolbachia pipiens, which is associated with
cytoplasmic incompatibility in Culex pipiens
Pallens (van Meer et al., 1995). The effect of
Wolbachia on parasitoid fitness is unclear. In
one study, female parasitoids treated with
antibiotics produced more offspring than
untreated females (Zchori-Fein et al., 1994),
whereas the opposite results were found in
another study (Stouthamer et al., 1994).
However, Wolbachiaspp. have clear effects
on oviposition behaviour and sex-specific
developmental requirements (Hunter, 1999).
Most sexual Encarsiaare obligate autopara-
sites: females lay fertilized female-producing
eggs in hosts, while unfertilized male-pro-
ducing eggs are laid in immature para-
sitoids. Cured E. formosafemales show a very
different behaviour. They deposit most of
their unfertilized eggs in their hosts and
males emerge exclusively from them
(Hunter, 1999). Antibiotic treatment induced
male production in two thelytokous popula-
tions of Encarsia meritoria Gahan (synonym
Encarsia hispida DeSantis). After treatment
with tetracycline, females of an Italian popu-
lation produced 81% male progeny
(Giorgini, 2001), whereas females of a
Spanish population produced almost
entirely male offspring (Hunter, 1999).PROTOZOA.An undescribed microsporidium
(Nosemasp.) found in the ovaries of Encarsia
nr.pergandiellafrom Brazil is associated with
a noted decline in fecundity in production
systems (Sheetz et al., 1997). The effects of
this microsporidium on the efficacy of
Encarsianr. pergandiellaare yet to be deter-
mined. The authors report that adult Encarsia
nr. pergandiella were effectively cured of
microsporidia when they were given a single
treatment of rifampicin administered in solu-
tion. However, it is not clear if the infection
status of the treated and untreated individu-
als were verified before the rifampicin was
administered. Nevertheless, this is the first
report of microsporidia in Encarsia, suggest-
ing that mass-produced Encarsiamay be sus-
ceptible to microsporidia.Eretmocerus(Aphelinidae): parasitoids of
whiteflies
BACTERIA.The thelytokous parasitoid
Eretmocerus staufferiRose and Zolnerowich is
host to parthenogenesis-inducing Wolbachia
(van Meer et al., 1999). Sequencing of the wsp150 S. Bjørnson and C. Schütte