Report

Invasive Harlequin Ladybird Carries Biological Weapons Against Native Competitors

Science  17 May 2013:
Vol. 340, Issue 6134, pp. 862-863
DOI: 10.1126/science.1234032

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Surprise Attack

Humans conduct the largest ecological experiment ever by continually moving species between continents. For example, the harlequin ladybird beetle, native to Asia, has become highly invasive in many regions after being introduced for biological control, but we do not understand why this species should so readily outcompete native ladybirds. Vilcinskas et al. (p. 862; see the Perspective by Reynolds) show that harlequin beetles have parasitic microsporidia within their hemolymph, which are fatal to other ladybird beetles that prey on harlequin beetle eggs and larvae. Harlequin beetles thus have an innate advantage over species that are otherwise equivalent in their abilities, but this sort of competitive advantage can be hard to spot.

Abstract

Invasive species that proliferate after colonizing new habitats have a negative environmental and economic impact. The reason why some species become successful invaders, whereas others, even closely related species, remain noninvasive is often unclear. The harlequin ladybird Harmonia axyridis, introduced for biological pest control, has become an invader that is outcompeting indigenous ladybird species in many countries. Here, we show that Harmonia carries abundant spores of obligate parasitic microsporidia closely related to Nosema thompsoni. These microsporidia, while not harming the carrier Harmonia, are lethal pathogens for the native ladybird Coccinella septempunctata. We propose that intraguild predation, representing a major selective force among competing ladybird species, causes the infection and ultimate death of native ladybirds when they feed on microsporidia-contaminated Harmonia eggs or larvae.

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