Infected portions of the organs are hypertro-
phied, due to the large number of spores that
occupy the cells (Lipa, 1968). In M. octodec-
imguttata, infection is observed in the gut
epithelium, which is frequently destroyed by
the pathogen (Lipa, 1968). Spores of N. coc-
cinellae are ellipsoidal and measure
4.4–6.7μm long by 2.3–3.4μm wide in fresh
smears (Lipa, 1968). N. coccinellaespores are
about 1 μm larger than those of N. hippo-
damiae, a microsporidium that infects the fat
body of H. convergensGuérin (Lipa, 1968).
Depending on the host species, up to 25% of
the beetle population may be infected with
N. coccinellae. There are no data, however,
that describe the effects of this microsporid-
ium on the efficacy of its hosts. The life cycle
of the microsporidium Nosema tracheophila
has been investigated in adult C. septempunc-
tata of the USA (Cali and Briggs, 1967).
Spores of this species are ovoid and measure
4.0–5.3μm long by 2.2–3.1μm wide. Infected
hosts do not show external signs of the dis-
ease. Spores are present in the haemocytes,
tracheal epithelium and connective tissue.
Even when heavily infected, spores are not
present in midgut cells or the fat body of C.
septempunctata, as is the case for N. hippo-
damiae.
FUNGI.The fungal pathogen B. bassianais an
important mortility factor in several over-
wintering coccinellid species in Poland,
including A. bipunctata, C. quinquepunctata, C.
septempunctataand H. quadripunctata (Lipa et
al., 1975; Hemptinne, 1988).
NEMATODES.Female C. septempunctata from
India may be parasitized by the solitary
mermithid nematode, Coccinellimermis. This
nematode may constitute 27% of the total
body weight (Rhamhalinghan, 1987). After
infection, juvenile worms curl up and
occupy the host haemocoel, where they may
inflict injuries on the heart (Rhamhalinghan,
1992). Obvious symptoms of nematode infec-
tion include a lower feeding rate, resulting in
malnutrition, a lower level of activity before
parasite emergence and paralysation after
parasite emergence. Secondary effects
include a lower haemocoel volume and
heart-beat frequency (Rhamhalinghan, 1992).
Coleomegilla: predators of aphidsBACTERIA.A male-killing trait in C. maculata is
heritable only through the female line and is
tetracycline-sensitive (Hurst et al., 1996). The
trait, however, is frequently absent early in
the reproductive cycle of the host. Some
females first produce both male and female
offspring but only female offspring are pro-
duced later on. Early clutches from such
females show good hatchability and females
emerging from these clutches do not show
the male-killing trait. The progressive nature
of the male-killing trait in C. maculatamay be
caused by a host–parasite conflict over trans-
mission (for a discussion, see Hurst et al.,
1996). The male-killing bacterium of C. macu-
latadiffers from the male-killer present in A.
bipunctata. The causal agent is most closely
related to Blattabacterium (Flavobacteria–
Bacterioides group), a host-beneficial sym-
biont found in cockroaches and some ter-
mites (Hurst et al., 1997). This first record of a
male-killing agent in the Flavobacteria–
Bacterioides group indicates that this trait
has evolved independently in different sym-
bionts and in many host species.FUNGI.Infection experiments have shown
that the entomopathogenic fungus B.
bassianamay be pathogenic toC. maculata. In
one study, beetles were susceptible to B.
bassianawhen they were directly contami-
nated by sprayed fungal conidia, whereas no
infection occurred when prey insects were
consumed from leaves that had been
sprayed (Lord et al., 1988).Harmonia: predators of aphidsBACTERIA.Several populations of H. axyridis
have been shown to occasionally produce
highly female-biased sex ratios (Matsuka et
al., 1975; Gotoh, 1982; Majerus et al., 1998).
This trait may be maintained within a popu-
lation over several generations and is mater-
nally inherited (Matsuka et al., 1975).
Moreover, several types of abnormal sex
ratio (SR) are present: the ‘complete SR’
(hatching rate half as high as for the normal
egg batches; only female adults develop), the
‘incomplete SR’ (hatching rate somewhat146 S. Bjørnson and C. Schütte