Ask The Entomologist

Amorous Beetles

With fire so near to us, and this oppressive ground-clinging smoke left after last night’s badly-needed rain, I’m reminded of beetles. Specifically, amorous beetles.

Wood-boring beetles, such as jewel beetles and long-horned beetles, are attracted by the smell of distressed trees. Burnt forests draw them in, as does the smell of wood on the air after I’ve been running the stump grinder.

But, much like humans, male jewel beetles are visual creatures. What really gets them in the mood for love is the sight of a female. Or something that looks a lot like a female.

The Emerald Ash Beetle is an invasive jewel beetle, currently approaching us from the East. It’s just a matter of time until it gets here, and entomologists are working hard at devising good traps for it. Traps are most effective when they match the beetles’ taste in mates’ colors – light green (preferred by the males) and purple (preferred by the females)…

Many insect traps also use sex pheromones to complete the illusion of “single bugs near you looking for love”. But either way, the fragrance of a distressed tree is a near-must if you want to attract its wood-boring insects.

In most cases, that is. Distressed plant scents aren’t always involved.

Julodimorpha bakewelli male having a good time with the most attractive female he’s ever met.
(photo credit: Darryl Gwynne – one of the two young entomologists who discovered this phenomenon)

Australia very nearly lost a large and very attractive species of giant jewel beetle, Julodimorpha bakewelli, thanks to male sexual confusion.

You see, just as in the Emerald Ash Borer, color and sheen are very important to the Australian Jewel Beetle. Females of this species are a lovely golden brown, with wingcases covered with little dimples that catch the light. To males of this species, the ideal female is one much larger than them – well-fed, healthy, and able to lay many eggs.

Unfortunately, textured beer bottles discarded along Australian highways proved irresistible to the male beetles. “Her size! Her color! The way she glimmers in the light!I’ve never known anyone this stunning”

It was simply impossible for females to compete for their males’ affections. All across Australia, female jewel beetles were spending nights alone by themselves in the Eucalyptus trees.

Meanwhile generations of males spent themselves on discarded beer bottles who never reciprocated their affections. The most beautiful female jewel beetle or a beer bottle? Males had a clear preference.

As the years went by, it became clear that the giant jewel beetle birth rate was severely affected. Surprisingly, the beer industry stepped in and designed a new bottle, less attractive to beetles. Thus saving the Australian Jewel Beetle from extinction. Here’s a brief video on the beer-bottle-loving beetles.

We can only dream of stumbling on something as attractive to control our lumber pests.

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