behaviour. Early-instar larvae require a con-
tinuous food supply, whereas adults feed lit-
tle during the first few days after pupal
emergence. Temperature stress affects C.
carneamortality to B. bassianaonly in combi-
nation with nutrition or starvation stress
(Donegan and Lighthart, 1989).
Fungi may also infect C. carnea larvae
when they are not subjected to stress.
Verticillium lecanii, B. bassiana and Paecilomyces
fumoso-roseus cause larval mortality, and toxic
effects on surviving individuals may be
traced until the fifth generation after inocula-
tion. Effects of these fungi on C. carnea include
decreased adult emergence, development of
teratogenic forms, hampered cocoon forma-
tion and decreased fecundity and predatory
rates (Pavlyushin, 1996).
Lady bird beetles (Coleoptera: Coccinellidae):
predators of aphidsSeveral groups of invertebrate pathogens’
symbionts have been recorded from the
Coccinellidae, including gregarines,
microsporidia, fungi, nematodes and sym-
bionts’ bacteria (Drea and Gordon, 1990;
Majerus and Hurst, 1997). A single pathogen
may be found within several coccinellid
species, bringing the host specificity of these
pathogens into question. Additional infor-
mation is needed to determine if native
pathogens from field-collected beetles are
encountered in mass-rearing systems.
During the past decade, male-killing sym-
bionts (maternally inherited bacteria that kill
male hosts during embryogenesis) have been
intensively studied in aphidophagous coc-
cinellids (for a review, see Majerus and Hurst,
1997). Within the Coccinellidae, there is more
than one agent of male lethality. Male-killing
is caused by a diverse array of inherited bac-
teria from three different groups (Mollicutes,
Proteobacteria, Flavobacteria-Bacterioides).
Maternally inherited male-killing symbionts
are associated with coccinellids of six differ-
ent genera, including Adalia bipunctata(L.),
Adonia variegata(Goeze), Coleomegilla maculata
(De Geer), Harmonia axyridis Pallas,
Hippodamia convergensand Menochilus sexmac-
ulatusFabricius (cited by Majerus and Hurst,
1997).
The habits of ladybirds (production of
eggs in clutches, sibling cannibalism, high
level of neonate larval mortality due to star-
vation and feeding on ephemeral prey) are
thought to have made them particularly
prone to male-killing symbionts. The pres-
ence of male-killing bacteria results in
resource allocation among siblings. By con-
suming their dead male siblings, newly
hatched female larvae increase their chances
of survival following dispersal. Furthermore,
low egg hatch in infected clutches reduces
the risk of cannibalism of female larvae by
their siblings (Majerus and Hurst, 1997).Adalia: predators of aphids
BACTERIA.Some strains of the two-spot lady-
bird beetle, A. bipunctata, and a strain of the
ten-spot ladybird beetle, Adalia decempunctata
L., are known to produce broods with a
strong bias towards females (Hurst et al.,
1992; von der Schulenburg et al., 2001) or
produce no male offspring at all (cited by
Matsuka et al., 1975; von der Schulenburg et
al., 2001). Egg hatches of A. bipunctatabroods
with distorted sex ratios were about half that
of broods with non-biased sex ratios due to
the death of male offspring early in their
development (Hurst et al., 1992). In both
Adalia species, the male-killing trait is herita-
ble only through the female line and is effi-
ciently transmitted from the adult female to
her female progeny. Following treatment
with tetracycline, adult females revert to pro-
ducing clutches with high hatch rates and a
normal 1:1 sex ratio (Hurst et al., 1992; von
der Schulenburg et al., 2001). These findings
indicate that the male-killing element is
probably a vertically transmitted bacterium.
At least four different bacteria cause sex-
ratio distortion in A. bipunctata: a Rickettsia
(Werren et al., 1994), a Spiroplasma(Hurst et
al., 1999b) and two strains of Wolbachia
(Hurst et al., 1999a). In one case, all four bac-
teria were present in a single sample of A.
bipunctata(Majerus et al., 2000). So far, only
one male-killing Rickettsia has been reported
in A. decempunctata(von der Schulenburg et
al., 2001). Phylogenetic analysis of Rickettsia
DNA sequences from different populations
of both Adaliaspecies revealed a single ori-144 S. Bjørnson and C. Schütte