The astonishing success of the alien invasive harlequin ladybird in Britain has given a team of scientists a unique opportunity to investigate a key ecological theory the Enemy Release Hypothesis.
The Enemy Release Hypothesis predicts that when a new alien species arrives into a country or region it is unlikely that the resident natural enemies will attack it.
Writing in the latest issue of the scientific journal Insect Conservation and Diversity the scientists conclude that, in the first ten years of the harlequin ladybird invasion the Harlequin arrived in the UK in 2004 it was much less likely to succumb to natural enemies (such as predators, parasites and pathogens) than the UK's native ladybird species such as the iconic 7-spot. Such natural enemies have evolved alongside native species and the research showed that they are less able to attack the new arrival.
The result may partly explain why the harlequin ladybird is such a successful invasive alien species supporting the notion that the harlequin is the "most invasive alien ladybird on Earth".
Ladybirds are generally not attacked by predators but there are a number of parasites - species that live in or on another species, so called hosts, deriving nutrients and usually resulting in death of the host - that exploit them. Ladybird parasites include wasps and flies (such as scuttles flies).
One of the most numerous ladybird parasites is a tiny wasp called Dinocampus coccinellae. It lays an egg inside a ladybird and subsequently hatches into a grub-like larva that devours the inside of the ladybird before emerging to pupate under the adult ladybird. It uses the adult ladybird as a bodyguard which twitches defensively above the small parasitic cocoon. The parasitic wasp emerges and the ladybird host dies.
The researchers monitored Harlequin ladybirds (Harmonia axyridis) and the native 7-spot ladybird (Coccinella septempunctata
|Contact: Barnaby Smith|
Centre for Ecology & Hydrology