Yesterday I wrote about biocontrol agents to manage aphid infestations. One species that was introduced from Asia to North and South America, Europe and Africa, for use in biological control programs is the harlequin ladybird Harmonia axyridis. Since its introduction in 1988 it has established populations in at least 38 countries and spreads at a rate of approximately 200 km/yr.
The harlequin ladybird is a large, voracious and resilient coccinellid beetle and has a long history of use as a classical biological control agent of aphids and scale insects since 1916. It is a highly polymorphic species (see image), with variation in colour morphs evident across its range, and has thus long been a study species for geneticists. Unfortunately, this species has itself become a pest. For example in the autumn, these beetles can aggregate in large numbers in vineyards and, if they are harvested along with the grapes, they release a chemical compound called methoxypyrazine that can spoil the aroma and taste of the wine. This species is also known to invade homes in October in preparation for winter, a phenomenon which earned it the common name of “Halloween lady beetle”. They try to overwinter indoors and there also have been reports that they occasionally bite humans.
However, the worst impact stems from a phenomenon called intraguild predation (IGP), i.e. the killing and eating of a species that uses similar, often limiting, resources. Here the targets are native species populations that are attached by Harmonia axyridis.
A new study published by a group of researchers from the UK, Belgium and the Netherlands is the first to use DNA Barcoding to identify prey species in the guts of harlequin ladybirds showing their damaging effect on native species. Their results strengthen the evidence that Harmonia axyridis is a very generalist predator. The researchers used barcodes to screen for four possible intraguild prey species (the two ladybirds Adalia bipunctata and Adalia decempunctata, as well as the hover fly Episyrphus balteatus and the lacewing Chrysoperla carnea) is occurring in the wild. Three of the four target prey species were detected in the guts of guts of 177 larvae field-collected in England, France, Germany, Slovakia and the Czech Republic: Adalia decempunctata, Adalia bipunctata and Episyrphus balteatus. The lacewing Chrysoperla carnea was not detected. Nevertheless, the results suggest that Harmonia axyridis feeding on alternative prey in the wild is commonplace and that can have negative effects on native species across a wide geographic area.
I am not sure if Harmonia the ancient Greek goddess of harmony likes her ever hungry namesake.