Scenta.co.uk, UK
03-26-07
The dark side of ladybugs
US scientists have gotten to the bottom of why ladybugs are such a nuisance to
crops, including vineyards.
The polka-dotted insects are producing a foul-smelling odour that not only
irritates farmers, but can inadvertently be processed along with grapes, tainting
the aroma and flavour of wine.
Iowa State University chemists now say that they have identified the
compounds responsible for the ladybug’s noxious scent, which could lead to new
strategies to detect and eliminate its effect.
A growing number of winemakers say that their wines have an abnormal aroma
and flavour, known as ‘ladybug taint’, which resembles the bug’s characteristic
odour.
Winemakers report that there are more ladybugs in vineyards and on the grapes
during harvest; experts believe that the bugs accidentally become mixed into the
juice during processing and fermentation, resulting in inferior wine.
Led by Jacek Koziel, an agricultural engineer at the university, the
researchers used a highly-sensitive multidimensional gas chromatograph and a
panel of human ‘sniffers’ to characterise and identify the odours emitted by a
group of live ladybugs – as many as 300 in all.
All of the ladybugs were from a single species of multicoloured Asian ladybird
beetle (Harmonia axyridis).
After sealing the bugs in test tubes in batches of five each, the odours they
emitted were carefully analysed by the researchers, who detected 28 different
scents.
Koziel and his team were then able to identify four chemicals that were most
likely to be responsible for the characteristic odour.
All of the chemicals belong to a class of compounds called methoxypyrazines,
which are potent odour-producing compounds also found in other animals and
plants.
A good bug turned bad
The compounds are not considered harmful to humans, but according to Koziel,
"even tiny amounts can be detected by the human nose".
Ladybugs are loaded with these foul-smelling compounds, he added.
The odour is used as a defensive mechanism against predators and has been
said to resemble the aroma of roasted peanuts or green bell peppers.
Because of the potency of the compounds, even a slight amount can potentially
affect a wine’s character, Koziel said.
However, ladybugs are generally considered beneficial insects.
Most notably, they are a significant source of biological control for aphids, tiny
plant-sucking insects that can damage several major crops.
Now, these beneficial insects are becoming a pest themselves by invading
homes, crops and vineyards.
"They are basically a good bug gone bad," said study co-author Matt O’Neal, an
entomologist at the university.
The study was presented at the 233rd national meeting of the American
Chemical Society.