Direct and indirect effect of cannibalism and intraguild predation in the two sibling 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   and specialist-rare   (Coleoptera: Coccinellidae). Direct predation effect of cannibalism and IGP was asymmetric in the two sibling ladybird beetles; the fourth instar larvae of . were better intraguild predators than cannibals, while the reverse was true in the larvae of  . Neither cannibalism nor IGP significantly affected female body weight in either species. Larval . surviving exposure to cannibalism or IGP had a reduced number of ovarioles as adults, whereas adult   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 . . In  , 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 . avoided the first instar conspecific larvae, while those of   were attracted to the odors from . and conspecifics. Thus, . has an avoidance mechanism only for cannibalism but not for IGP whereas   does not have any avoidance mechanism. These different behaviors in the direct and indirect effects of cannibalism and IGP observed in the laboratory may play important roles in the coexistence of generalist-common . and specialist-rare   in natural conditions, compensating for the large handicap of   at reproductive interference from . .