| Austroplatypus incompertus | |
|---|---|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Coleoptera |
| Family: | Curculionidae |
| Genus: | Austroplatypus |
| Species: | A. incompertus |
| Binomial name | |
| Austroplatypus incompertus Schedl, 1968 |
|
Austroplatypus incompertus is a species of weevil native to Australia with a verified distribution in New South Wales and Victoria.[1] It forms colonies in the heartwood of Eucalyptus trees and is the first beetle to be recognized as a eusocial insect.[2][3]
Contents |
The eggs of A. incompertus are approximately 0.7 mm in length and 0.45 mm wide. They develop through five instars and their head grows from approximately 0.3 mm wide in the first instar to 0.9 mm wide in the fifth instar. They then pupate and hatch as adults that are approximately 6 mm long and 2 mm in diameter. Adults display sexual dimorphism with males being the significantly smaller sex, an atypical arrangement among platypodine beetles.[4]
The common name ambrosia beetle is applied to this and about 300 other weevils in the subfamilies Scolytinae and Platypodinae (Coleoptera, Curculionidae) that fill a similar ecological niche by living colonially (although not necessarily eusocially) inside trees and cultivating the same type of fungi.[2]
Like other ambrosia beetles, A. incompertus lives in nutritional symbiosis with ambrosia fungi. They excavate tunnels in dead trees in which they cultivate fungal gardens as their sole source of nutrition. New colonies are founded by fertilized females who use special hair-like 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.[3] Fertilized females begin tunneling into trees in the autumn and take about seven months to penetrate 50 mm to 80 mm deep to lay their eggs.[3][2]
An assessment done by the United States Department of Agriculture on unprocessed logs and chips of eighteen woody plants 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.[5]
A. incompertus has been called "the Australian beetle that behaves like a bee"[2] because it displays those "three phenomena which characterize eusociality"[6] and are most associated with various species of Hymenoptera. Firstly, colonies contain individuals of overlapping generations. Secondly, they engage in cooperative broodcare. Thirdly, their population is divided into reproductive and unfertilized, non-reproductive castes. Their colonies are small; each contains a single fertilized female and approximately five non-breeding females who defend the breeding female against predators and do the work of digging more galleries in which to raise fungus.[3][6]
Haplodiploidy, leading to the sharing of a high proportion (0.75) of genes between sisters, has been regarded by some as critical in explaining the evolution of eusociality in hymenopterans. Study has shown, however, that A. incompertus males and females are diploid, thus providing evidence against the notion that the haplodiploidy hypothesis might be similarly applied to the phylogenetically diverse non-hymenopteran taxa among which eusociality and other altruistic behaviors have evolved.[3]