no offspring or only sterile males, whereas
the cross of infected females with uninfected
males yields viable offspring (cited in
Breeuwer and Werren, 1990). In Nasonia,
Wolbachiaspp. cause paternal chromosome
loss in incompatible crosses, whereby the
paternal chromosomes fail to condense prop-
erly, become fragmented and are lost in fer-
tilized eggs. This results in the production of
all-male lines (Breeuwer and Werren, 1990).
Nasoniamay be cured of Wolbachiaendosym-
bionts with antibiotics or by prolonging lar-
val diapause (Breeuwer and Werren, 1990;
Perrot-Minnot et al., 1996).
Wolbachia spp. are associated with the
reproductive isolation of N. vitripennisand
N. giraulti (Breeuwer and Werren, 1990).
These two species mate readily but only
male progeny are produced. However, elimi-
nation of Wolbachiaby antibiotic treatment
allows the two species to produce viable
hybrids (Breeuwer and Werren, 1990).
Two independent studies on the phylogeny
of Wolbachiausing the 16S rDNA gene and the
ftsZ gene showed that Nasonia spp. may be
infected by two different species of Wolbachia
(Breeuwer et al., 1992; Werren et al., 1995).
Males from double-infected strains show typi-
cal unidirectional cytoplasmic incompatibility
with single-infected females. Males of single-
infected strains, however, show bidirectional
incompatibility, meaning that all crosses are
incompatible (Perrot-Minnot et al., 1996).
Reports on the effect of Wolbachiaon host
fitness are controversial. Stolk and
Stouthamer (1996) found a positive fitness
effect in one strain of N. vitripennisand no
effect in another strain. Here fitness was mea-
sured as lifetime fecundity. Preliminary tests
done by Bordenstein and Werren (2000) also
suggest a positive effect of Wolbachia,but no
consistent positive effect was found once host
genetic background was controlled for.
UNIDENTIFIED DISEASE.A field-collected strain
of N. vitripennis produced few or no male
offspring. This factor, termed msr, causes
97% female families and is maternally inher-
ited (Skinner, 1982). Experimental results
suggest that the observed sex ratios are not
caused by the mortality of male offspring, as
is the case with Arsenophonus nasoniae.
Opius(formerlyBiosteres) (Braconidae):
parasitoids of fruit fliesBACTERIA.Severe mortality of premature
adult parasitoids may occur in laboratory
cultures of Opius longicaudatus(Ashmead).
Parasitoid mortality may exceed 80%
(Greany et al., 1977). The most common bac-
teria isolated from these parasitoids are
Serratia marcescens, Proteus mirabilis,
Pseudomonas aeruginosaand Enterobacter cloa-
cae. Although these bacteria are also present
in the host (the Caribbean fruit fly,
Anastrepha suspensa (Loew)), the incidence of
bacteria is highest in newly deceased para-
sitoids (Greany et al., 1977). Parasitoid mor-
tality is probably caused by stress-induced
septicaemia of several species of opportunis-
tic bacterial pathogens. Parasitoid mortality
may be controlled by rearing B. longicauda-
tus under optimal conditions without the
use of antibiotics (Greany et al., 1977).Pediobius (Eulophidae): parasitoids of
Mexican bean beetlesPROTOZOA.Pediobius foveolatus(Crawford) is
highly susceptible to Nosema epilachnaeand
Nosema varivestis, two microsporidia that
also infect its host, the Mexican bean beetle
(Epilachna varivestisMulsant). Both N. epilach-
naeand N. varivestis are detrimental to P.
foveolatus(Own and Brooks, 1986; Chapman
and Hooker, 1992).
In beetles that are heavily infected with N.
epilachnae, most progeny (96%) become
infected and many of them are unable to
complete development. Parasitoid mortality
occurs primarily in the pupal stage. Of the
parasitoids that are able to emerge from their
infected hosts, many appear normal.
However, about one-third exhibit obvious
malformations, including malformed wings,
greatly distended abdomens or both.
Microsporidian spores are observed in all
adult tissues. N. epilachnaedoes not affect the
developmental period of emerging adults
but adult longevity is significantly reduced.
Adult parasitoids are susceptible to spores
when administered per osand N. epilachnaeis
transmitted mechanically during oviposition
(Own and Brooks, 1986).Pathogens of Natural Enemies and Pollinators 153