Christmas beetles can defoliate whole eucalyptus trees causing dieback in mature trees.
Christmas beetles arrive on cue
Why do Christmas beetles appear quite suddenly, sometimes in large numbers leading up to the holiday season in Australia?
13 December 2007 | Updated 8 February 2013
Christmas beetles (Anoplognathus species) are members of the family Scarabaeidae.
There are 34 species of Christmas beetle distributed throughout Australia, although most species occur in the higher rainfall areas of the southern and eastern states.
Adults beetles are usually between 20 and 30 millimetres in length, have small clubbed antennae and spiky legs.
Depending on the species, Christmas beetles come in a range of colours including:
pale to dark brown
Christmas beetle larvae have a distinctive 'C' shape and are often called curl grubs.
They inhabit the soil throughout grassland areas, and can be found in:
Why do Christmas beetles appear at Christmas
Christmas beetles have a seasonal life cycle, which may be annual or biennial depending on the climate of a particular region.
From December to January adult Christmas beetles mate and lay eggs into the soil surface.
Christmas beetles are large glossy brown beetles often seen clustered on the leaves of eucalypt trees during the Australian summer.
Larvae develop through three stages (instars), and in warmer areas of the country spend one winter in the soil, emerging as adults the following spring.
In cooler parts of the country larvae spend two winters in the soil.
Under cooler conditions larvae only reach the second instar in the season following laying.
They continue to grow and develop for another season before pupating.
Several waves of emergence can occur from late November through to February depending on:
Christmas beetles emerge late afternoon and can fly distances of several kilometres. Most flights occur at dusk, with beetles often attracted to outdoor lighting.
What influences Christmas beetle numbers
Christmas beetles pupate from late spring to early summer in a chamber near the soil surface.
Emergence is often triggered by rain which moistens the soil enough for fully developed beetles to dig there way to the surface.
During dry conditions, Christmas beetles may remain inactive in the pupal chamber for a few weeks.
In very dry conditions adults can perish in the soil waiting for suitable rains.
Winter rains enhance larval survival and after spring rains or thunderstorms mass emergence can often occur as the ground becomes moist enough for adults to emerge.
Christmas beetle impacts
Christmas beetles are voracious eaters and are capable of attacking a wide range of eucalypts and other tree species.
Adult Christmas beetles make zigzag cuts to leaves as they feed, shredding leaves with much leaf material wasted and falling to the ground.
Trees can be defoliated in a very short time, particularly by beetles feeding in swarms.
Swarms can often occur in waves from late spring to early summer, depending on favourable weather conditions.
Christmas beetles often show a preference for particular species, even individual trees within a species.
Repeated defoliations over several seasons may lead to dieback over vast areas of eucalypt woodlands and can even kill mature trees.
The Christmas beetle larvae feed underground on organic matter such as roots and grasses, causing little damage.
CSIRO Entomology is not currently researching Christmas beetles.
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