higher; few male adults develop) and the
‘progressive SR’ (normal hatching rate; male
and female offspring develop from egg
batches laid during the initial oviposition
period, whereas egg batches deposited later
on yield only females with a low hatching
rate). In two cases, ‘cured’ females devel-
oped spontaneously from female-biased
lines. In another study, three populations of
H. axyridisshowed a high variance in the
presence of the male-killing trait (Majerus et
al., 1998). This trait was absent in a Russian
population, whereas approximately 2% and
49% of the females carried the trait in a
Japanese and a Mongolian population,
respectively. The trait has high vertical-trans-
mission efficiency and is antibiotic-sensitive.
Antibiotic treatments (tetracycline and chlo-
ramphenicol) fail to produce an increase in
egg hatch rates in H. axyridis exhibiting
abnormal sex ratios. However, antibiotic
treatment results in a significant increase in
the proportion of eggs showing embryonic
development. Treatment of H. axyridiswith
abnormal sex ratios does not usually effect a
complete cure (Majerus et al., 1998).
As is the case for A. bipunctata, several
distinct bacteria may cause heterogeneous
male-killing in H. axyridis. However, only
one causal agent has been detected.
Molecular analysis of a Russian line bearing
a maternally inherited male-killing trait
revealed the presence of a bacterium belong-
ing to the genus Spiroplasma(Zakharov et al.,
1999). The Spiroplasmafrom H. axyridisis not
identical to the one detected in A. bipunctata.
A more detailed study of geographically dis-
tant Japanese populations revealed the pres-
ence of an identical Spiroplasma in two
populations of H. axyridis (Majerus et al.,
1999). A spiroplasm-specific PCR verified
the presence of Spiroplasmain all-female and
predominantly female H. axyridis popula-
tions, whereas it was absent in individuals
from normal populations. Bacteria are pre-
sent in lymph and haemocytes only in popu-
lations showing the male-killing trait.
Phylogenetic analysis revealed that the bac-
terium is most closely related to Spiroplasma
ixodetis, a Spiroplasma from ticks, and the
male-killing Spiroplasma from A. bipunctata
(Majerus et al., 1999).
PROTOZOA.The gregarine G. coccinellae was
recorded in H. quadripunctataduring a field
study on hibernating coccinellids in Poland
(Lipa et al., 1975). The immature stages of
this gregarine develop in the epithelial cells
of the midgut, whereas the mature sporonts
live in the gut lumen (see section on
Coccinella, above).FUNGI.The entomopathogenic fungus B.
bassiana was detected on hibernating H.
quadripunctata (Lipa et al., 1975) and is
thought to be an important mortality factor
in hibernating coccinellids (Lipa et al., 1975).Hippodamia: predators of aphidsBACTERIA.Abnormal sex ratios have been
reported in Hippodamia quinquesignata
(Kirby) collected in Utah. The trait is mater-
nally inherited (Shull, 1948). It is not known
if the sex-ratio distortion is due to the pres-
ence of bacteria, as is the case for A. bipunc-
tata, C. maculata andH. axyridis.
James and Lighthart (1992) tested the sus-
ceptibility of H. convergensto the weak bacte-
rial pathogen Pseudomonas fluorescens. This
facultative pathogen may invade the haemo-
coel of the host and cause septicaemia, even-
tually leading to the death of the host.
Fourth-instar larvae are more resistant to P.
fluorescens than earlier-instar larvae. A poor
diet offered at 25°C decreases the susceptibil-
ity of first-instar larvae to P. fluorescens,
whereas starvation at a high temperature
(30°C) increases susceptibility to the bac-
terium (James and Lighthart, 1992).
Two species of ice-nucleating active (INA)
bacteria, Enterobacter agglomerans and
Enterobacter taylorae, were isolated from the
gut of field-collected H. convergens(Lee et al.,
1991). INA bacteria are unique in their capac-
ity to catalyse ice nucleation at temperatures
as high as 1–2° below 0°C. Ingestion of INA
bacteria cause freezing of H. convergensat
temperatures as high as 1.5°C, whereas
unfed beetles and those fed sterile water or
the non-INA bacterium Escherichia colifreeze
at 16°C to 17°C. The effects of INA bacte-
ria on hibernating H. convergensunder field
conditions are not yet known.Pathogens of Natural Enemies and Pollinators 147