Data from: Direct and indirect effect of cannibalism and intraguild predation in the two sibling Harmonia ladybird beetles

In this study, we focused on the direct (i.e. predation) and indirect
(i.e. potential threat from coexisting with a larger individual) effects
of cannibalism and intraguild predation (IGP) during larval stages of two
sibling ladybird beetles. These effects play an important role in the
coexistence of the generalist–common Harmonia axyridis and specialist–rare
H. yedoensis (Coleoptera: Coccinellidae). Direct predation effect of
cannibalism and IGP were asymmetric in the two sibling ladybird beetles;
the fourth instar larvae of H. axyridis were better intraguild predators
than cannibals, while the reverse was true in the larvae of H. yedoensis.
Neither cannibalism nor IGP significantly affected female body weight in
either species. Larval H. axyridis surviving exposure to cannibalism or
IGP had a reduced number of ovarioles as adults, whereas adult H.
yedoensis ovarioles were not affected. For the indirect effects, longer
developmental times in males and females and a lower total number of
ovarioles in females were detected in H. axyridis. In H. yedoensis,
shorter developmental time of males, lighter adult weight and fewer total
ovarioles in females were observed. Olfactometer choice experiments
clarified that the fourth instar larvae of H. axyridis avoided the first
instar conspecific larvae, while those of H. yedoensis were attracted to
the odours from H. axyridis and conspecifics. Thus, H. axyridis has an
avoidance mechanism only for cannibalism but not for IGP, whereas H.
yedoensis does not have any avoidance mechanism. These different
behaviours in the direct and indirect effects of cannibalism and IGP
observed in the laboratory may play important roles in the coexistence of
generalist–common H. axyridis and specialist–rare H. yedoensis in natural
conditions, compensating for the large handicap of H. yedoensis at
reproductive interference from H. axyridis.