Egg Predation by the Introduced Lady Beetle, Coccinella septempunctata (Coleoptera: Coccinellidae), Lowers Mortality but Raises Relative Risk for the Native Lady Beetle, Coccinella novemnotata

Abstract

Populations of the native ninespotted lady beetle, Coccinella novemnotata Herbst, have undergone precipitous declines in North America following the establishment of the exotic sevenspotted lady beetle, Coccinella septempunctata L. Recent volunteer efforts have made it possible to establish colonies of the now-rare C. novemnotata and test mechanisms contributing to its decline. We evaluated the relative frequencies of intraguild predation and cannibalism of eggs between these two species. A single C. novemnotata or C. septempunctata adult was exposed to conspecific and heterospecific eggs in either the presence or absence of pea aphids. The study revealed two expected results: 1) eggs of C. novemnotata were consumed more frequently than eggs of C. septempunctata by both species, and 2) egg consumption was higher when aphids were absent, independent of predator and egg species. There were also two unexpected results from the study: 1) the asymmetry between egg predation rates was higher when aphids were present, and 2) higher predation rates on C. novemnotata eggs in the absence of alternate prey was due to a relatively higher rate of intraspecific cannibalism. This implies that C. novemnotata would have suffered higher egg mortality rates before the invasion of C. septempunctata, but even though the aggregate rate of egg predation on C. novemnotata eggs is lower post-invasion, it is still significantly higher than the aggregate rate of predation of C. septempunctata eggs. This differential pattern of asymmetric predation could contribute to habitat compression and the overall decline of C. novemnotata.

Fates of Rare Species under Siege from Invasion: Persistence of Coccinella novemnotata Herbst in Western North America alongside an Invasive Congener

“…The importance of alternative causes received support from subsequent documentation that C. novemnotata's steep decline in Missouri occurred well before C. septempunctata arrived (Fothergill and Tindall, 2010;Diepenbrock et al, 2016). Nonetheless, the arrival of C. septempunctata and its potential competitive and predatory impact on C. novemnotata, as explored in the laboratory (Hoki et al, 2014;Kajita et al, 2014;Turnipseed et al, 2014Turnipseed et al, , 2015Ugine and Losey, 2014;Tumminello et al, 2015), raises the possibility that C. septempunctata may now diminish prospects for recovery, and indeed may drive to critically lower levels, populations of C. novemnotata previously reduced to low numbers even before its arrival.…”

Investigations on the cannibalistic behavior of ladybird beetle Coccinella septempunctata L. (Coleoptera: Coccinellidae) under laboratory conditions

“…Poor diet quality also exerts pressure on predators to feed on conspecifics. However, higher aphid densities may result in a lower encounter rate of ladybirds with eggs than aphids and may lead to reduced egg consumption (Snyder et al, 2000;Turnipseed et al, 2015). Agarwala (1991) stated that egg cannibalism in ladybirds occurred at all aphid densities but was more pronounced at lower densities.…”

Circumventing regulatory safeguards:Laricobiusspp. and biocontrol of the hemlock woolly adelgid

“…While the parasitoid Aphytis lingnanensis was not sufficient for California scale control in citrus, Aphytis melinus was (Murdoch et al, 1996). Competition and egg predation by an introduced lady beetle Coccinella septempunctata on its native North American congener C. novemnotata are implicated in the decline of the latter (Turnipseed et al, 2015;Ugine et al, 2018). This is further exemplified by the failure of native L. rubidus to control HWA in eastern North America and the belief nevertheless that congeneric L. nigrinus and L. osakensis will do so.…”

“…The red imported fire ant, Solenopsis invicta, is a devastating invader in the southeastern United States (Tschinkel, 2006), while its congener, Solenopsis geminata, likely also introduced (Wilson & Brown, 1958), is relatively innocuous, restricted to a narrower range of habitats (McInnes, 1994) and with relatively minor behavioural traits perhaps accounting for differing impacts (Simberloff, 1985). Competition and egg predation by an introduced lady beetle Coccinella septempunctata on its native North American congener C. novemnotata are implicated in the decline of the latter (Turnipseed et al, 2015;Ugine et al, 2018). While the parasitoid Aphytis lingnanensis was not sufficient for California scale control in citrus, Aphytis melinus was (Murdoch et al, 1996).…”