From Asia with devastation

Hawaii was first to be invaded in the shadow of the Cold War, in the 1980s. Just under a couple of decades later, an attack was launched upon mainland USA. The first troops made landfall in 2008, in California. Over the next two years the front line progressed eastwards and now the whole of the USA is enemy territory. Meanwhile a stealthy attack was being launched on Europe, with many Western countries such as Italy, France, Belgium and Spain besieged. Six years ago, in 2012, the UK fell under fire. Drosophila suzukii had arrived from South-east Asia, with consequences.

The genus Drosophila is massive, with around 1,500 species described. One species, Drosophila melanogaster, is famous for its use in genetics and developmental biology experiments; they are “lab flies”. When one uses the phrase “fruit flies”, one is usually referring to this genus. Despite their frugivorous (fruit-eating) habits, they are, on the whole, fairly harmless to the fruit industry. This is because the vast majority of them lay their eggs in rotting fruit, while fruit pickers obviously tend to choose fruits that are ripe or not yet ripe. Therefore, Drosophila species have no impact on fruits prior to harvesting. Except for Drosophila suzukii, that is.

Drosophila suzukii has one minor difference in its lifecycle that has earned it the infamy of being one of North America’s most prolific crop pests. The females possess on their ovipositor (from which the eggs are laid) a serrated knife-like structure which can slice through the skins of fruits like cherries and blueberries. This allows the species to thrive in and damage fruits prior to harvest, while other species have to wait until decomposition has rendered the fruits soft enough to lay eggs in without relying on cutting into them.

Finding this species in my very own garden really drove this worldwide colonisation home (almost literally). It is amazing to think that, having lived in the same house for my entire life, if I’d hung some banana slices from our plum tree – like I did last week – up until I was nine in 2012, I probably wouldn’t have found this prolific invader. Yet, sometime between then and now, Drosophila suzukii has winged its way into our village and begun to breed. Below is an image of the tiny fly, around 2.5 mm in length, which has hitched a series of lifts aboard ships and other vehicles around the world from its native home in South-east Asia to appear at my doorstep. Little does it know about the billions of dollars of crop damage its species has caused along the way.

Drosophila suzukii male crop

The male of Drosophila suzukii is distinguished by the black spots near the apex of the wings

 

 

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