Austroplatypus incompertus

Austroplatypus incompertus is a species of ambrosia beetle belonging to the weevil family, native to Australia, with a verified distribution in New South Wales and Victoria. It forms colonies in the heartwood of Eucalyptus trees and is the first beetle to be recognized as a eusocial insect. Austroplatypus incompertus is considered eusocial because groups contain a single fertilized female that is protected and taken care of by a small number of unfertilized females that also do much of the work.

The egg of A. incompertus is about 0.7 mm in length and 0.45 mm wide. It develops through five instars and its head grows from around 0.3 mm wide in the first instar to 0.9 mm wide in the fifth instar. It then pupates and emerges as an adult - 6 mm long and 2 mm wide. The adult has an elongated, cylindrical body typical of other platypodines, and displays sexual dimorphism, with males being the significantly smaller sex, an atypical arrangement among platypodine beetles. Females have elytral declivity adapted for cleaning of galleries and defense. Also, only females exhibit mycangia.

Like other ambrosia beetles, A. incompertus lives in nutritional symbiosis with ambrosia fungi. They excavate tunnels in living trees in which they cultivate fungal gardens as their sole source of nutrition. New colonies are founded by fertilized females that use special structures called mycangia to transport fungi to a new host tree. The mycangia of A. incompertus and the specific manner in which the species acquires fungal spores for transport have been studied and compared with the mechanisms used by other ambrosia beetles. Fertilized females begin tunneling into trees in the autumn and take about seven months to penetrate 50 to 80 mm deep to lay their eggs.

An assessment done by the United States Department of Agriculture (USDA) on unprocessed logs and chips of 18 woody-plant species from Australia discovered A. incompertus in most of them, including: Eucalyptus baxteri, E. botryoides, E. consideniana, E. delegatensis, E. eugenioides, E. fastigata, E. globoidea, E. macrorhyncha, E. muelleriana, E. obliqua, E. pilularis, E. radiata, E. scabra, E. sieberi, and Corymbia gummifera. Unlike most ambrosia beetles, it infests healthy, undamaged trees.

A. incompertus is local to Australia, and has been confirmed to be found in various places around New South Wales. Their range is somewhat limited, extending north to Dorrigo and west to the Styx River State Forest.

A fertilized female attempts to start a new colony by burrowing deep into the heart of a living tree, eventually branching off and depositing her fungal spores and larvae. When these larvae grow to adulthood, the males leave some time before the females, with an average of five females remaining behind, and quickly lose the last four tarsal segments on their hind legs. The sole entrance to the colony shortly thereafter will be closed by the tree, enclosing the colony. This deformity and physical barrier causes females to remain unfertilized and they participate in maintenance, excavation, and defense of the galleries, propagating the maintenance of the social hierarchy.

This page was last edited on 23 March 2018, at 03:29.
Reference: under CC BY-SA license.

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