Eucalyptus Tortoise Beetle Larva

Description:

Larvae about 5mm long with broad shiny head and pro-thoracic segment. Tubercles seen on every segment of the body. When disturbed, the larvae reared-up the hind end in an "s" shape and a pair of transparent horn-like structures shot out of the dorsal side of rear-end (pic #1), the structures were retracted as soon as the threat disappeared - partial retraction seen in pic #2. These are defense glands. The larva also seemed to produce a yellow liquid through its mouth. Most of the larvae were in pairs as in pic #5

Habitat:

Eucalyptus tree

Notes:

I assumed these were leaf beetle larvae but have never seen the "horn-like" structures before. On the same tree were old paropsid beetle egg clusters and clumps of small larvae - probably 1st instar. Thanks to martinl for confirming this. These are the 4th instar of the eucalyptus leaf beetle. "Like several other paropsine species (see Simmul & de Little 1999), larvae of P. atomaria are highly gregarious, particularly in earlier instars (Carne 1966). Larvae defend themselves by elevating their posterior end and everting defensive glands that secrete hydrogen cyanide, benzaldehyde and glucose (Moore 1967). Towards the end of the fourth instar the larvae drop to the ground and form pupal cells several centimetres below the surface (Cumpston 1939). Pupation occurs five days after cell formation and adults emerge approximately ten days later. Females are ready to oviposit three weeks after emergence (Carne 1966)." Source: Australian Journal of Entomology, 47.