ECOLOGY

Herbivores & insects

Some acacias produce toxic, cyanogenic chemicals which may act as a defence against herbivores, but most Acacia foliage appears to be eaten by some animal and any defences produced by the plant are ultimately overcome. Native vertebrate herbivores of Acacia are few. However, wallabies (Wallabia bicolor) have been observed to eat wattle seedlings, and probably other macropods and wombats will also eat the seedlings. Sheep, goats and rabbits will also damage seedlings, and the latter are known to strip the bark from Mulga trees (Acacia aneura) in times of drought, ringbarking and killing the trees. There are, however, numerous insects which attack acacias. Most phyllodinous species are subject to 'leaf' mining by the larva of moths and butterflies (Lepidoptera). Some of these are associated exclusively with Acacia species, and a few attack only closely related species. The larva of the nocturnal feeding Bag-shelter Moth (Ochrogaster contraria: Thaumetopoeinae) which remains in a web covered nest at the base of the plant during the day can completely defoliate a shrub. Other herbivores include phyllode eating moth larva and sap sucking insects such as leaf hoppers, white flies, scale insects and mealy bugs and lerps.

Many wood boring beetles and larva attack the stems, branches or roots. The Longicorn Beetles (genera Ancita, Platymomopsis, Rhytiphora and Penthea: Cerambycidae (Lawrence & Britton 1994) and Wood Moths (Cryptophasa sp.: Xyloryctidae) (Hadlington & Johnson 1996) are common wood borers which can severely damage the stems of plants. The entry hole is often covered by grass held together with web. The larva of several species of butterfly (family Lycaenidae), frequently attack the roots, and the Witchety Grub (the larvae of the Cossid moth - Xylentes leucomochla: Cossidae) has as its host the roots of Acacia ligulata. The attractive adult green or blue and black Diamond Beetle or Botany Bay Weevil (Chrysolopus spectabilis: Curculionidae) feeds on Acacia foliage, and the larvae which live in the stems and roots can destroy shrubs and young trees (Lawrence & Britton 1994). The adult weevil is also suspected of ringbarking the branches which causes their death. The Wattle Pig weevil (Leptopius sp.: Curculionidae) lives in the soil and feeds on the roots.

Beetles, weevils (particularly Melanterius sp.: Curculionidae) (Lawrence & Britton 1994) and some wasps oviposit into young seeds. The developing larva consume the seed and finally drop to the ground to pupate when the pods mature. Pods and seeds are also damaged by being pierced and sucked by some bugs, such as Riptortus sp.: Alydidae (Zborowski & Storey 1995). Seeds are also eaten by Galahs (Cacatua roseicapilla) and Cockatoos (Cacatua galerita) (Keast, Recher, Ford & Saunders 1985), and the Eastern Rosella (Platycercus eximius) has been observed eating the immature green seed pods of Acacia crassa. A number of parrots and cockatoos are cited (Forshaw & Cooper 1973) as feeding on acacias, presumably the legumes and seeds, with the Black Cockatoo (Calyptorhynchus funereus) also taking the wood boring lavae of cossid moths and cerambycid beetles.

Insectiverous birds, such as Brown and Yellow Thornbills (Acanthiza pusila, A. nana), Rose Robbins (Petroica rosea) and Fantails (Rhipidura spp.), and others, such as Noisy Miners (Manorina melanocephala) regularly feed on the invertebrates associated with acacias (Keast, Recher, Ford & Saunders 1985). These authors also report the feeding on wasp larvae in the galls of Acacia species by the Little Corellas (Cacatua sanguinea).

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