have higher fecundity than uninfected
strains. Moreover, antibiotic treatments can
reduce fecundity in the high-fecundity line
(30 eggs per female per 5 days in the treated
line versus 60 eggs in the untreated line),
suggesting that Wolbachiaspp. are associated
with an increase in parasitoid fecundity
(Vavre et al., 1999).
PROTOZOA.The microsporidium Nosema
pyrausta causes chronic disease in the
European cornborer, Ostrinia nubilalis
(Hübner). Trichogramma evanescens
Westwood is also susceptible to the
microsporidium and N. pyrausta may persist
in field populations where T. evanescensis
released for cornborer control. Stained
preparations of infected T. evanescensshow
heavy infection of several tissues, including
the alimentary tract, fat body, Malpighian
tubules and muscle and nervous tissue. In
some cases, the abdomen is filled with
microsporidian spores. Microsporidia-
infected T. evanescens females produce about
half the progeny that are produced by unin-
fected females. Transovarial transmission of
N. pyrausta does not occur in T. evanescens.
However, the incidence of infection in devel-
oping parasitoid larvae is dependent on the
number of O. nubilaliseggs that are infected
with the microsporidium (Huger, 1984).
T. nubilalethat develop in N. pyrausta-
infected O. nubilaliseggs are directly affected
by the microsporidium. Microsporidian
spores are confined to the gut lumen of T.
nubilale larvae but are found in the gut
epithelium, and in muscle and nervous tis-
sues of adult and pupal stages. The
microsporidium impairs larval–pupal devel-
opment and reduces adult emergence and
fecundity (Sajap and Lewis, 1988). T. nubilale
does not discriminate between healthy hosts
and those infected with N. pyrausta. Fewer
and smaller adult parasitoids emerge from
infected host eggs than from uninfected eggs
(Saleh et al., 1995).
A microsporidium of the genus
Vairimorphainfects the cabbage moth Plutella
xylostella (L.). This microsporidium is transo-
varially transmitted between generations of
the host but has little impact on its fitness.
However, Vairimorphasp. has a detrimental
impact on T. chilonis, a parasitoid of P.
xylostella. The microsporidium develops in
various tissues, including the flight muscles
and nervous tissues. Microsporidian-infected
parasitoids show abnormal development
and their longevity and fecundity are
reduced. Successful biological control strate-
gies are dependent on rearing these para-
sitoids on disease-free host eggs and making
several releases in areas where endemic
hosts are known to be infected (Schuldet al.,
1999).Pollinators (Hymenoptera)Bombus(Hymenoptera, Apidae): pollinators
A large number of pathogens have been
described from bumblebees (for recent
reviews, see MacFarlane et al., 1995; Schmid-
Hempel, 1998). However, the effects and epi-
demiology of many of these pathogens are
unknown.VIRUSES.Two types of viruses are recorded
from bumblebees. An acute bee paralysis
virus is pathogenic to both the honeybee
(Apis melliferaL.) and several Bombusspecies.
The effects of an entomopoxvirus isolated
from Bombus fervidusFabricius, Bombus impa-
tiens Cresson and Bombus pennsylvanicus
DeGeer from the USA are not known (cited
by MacFarlane et al., 1995).BACTERIA.Spiroplasma melliferumcauses May
disease or pollen intoxication in honeybees.
Although this spiroplasma is isolated from
the haemolymph of B. impatiensand B. penn-
sylvanicusfrom North America, the effects of
S. melliferumon bumblebees have not been
determined. Aerobacter cloacae causes B-
melanosis, a disease affecting the ovaries of
honeybee queens. Although A. cloacaehas
been isolated from bumblebee queens, the
effects of this bacterium on bumblebees are
not clear (Schmid-Hempel, 1998). Gram-pos-
itive, spore-forming bacteria associated with
diseased Bombus melanopygusNylander lar-
vae from the USA cause infected larvae to
harden and be susceptible to fungal infection
(cited by MacFarlane et al., 1995).Pathogens of Natural Enemies and Pollinators 155