Why were cane toads introduced in Australia?

Answer 1

Cane toads were imported by the Australian Bureau of Sugar Experimental Stations to eat cane beetles. The beetles were a major pest of sugar cane and threatened to ruin the industry. The Greyback and French's Cane Beetles, native insects that naturally ate grass roots, bored into the roots of sugar cane crops and were causing the plants to die and go brown. Control with poisons like arsenic trioxide, carbon disulfide and even 1,4 dichlorobenzene was failing badly, and the success of biological control against he prickly pear led influential politicians and the CSIR to believe the toad would eat the beetles.

Unfortunately, toads cannot access adult beetles which fly away and the larvae live underground, so the experiment was a failure. European common toads (Bufo bufo) were tested for controlling grass grubs, but it was found they could not dig down to reach them - a basic quarantine process never done with cane toads.

Since none of Australia's native animals have resistance to bufotenin (unlike other places where cane toads have been introduced), they have become more of a pest than the beetles ever were. Quolls, medium-sized carnivorous marsupials, have been very badly hit by poisoning from toads and now are largely confined to Tasmania where toads cannot reach (they sink in seawater). Many snakes have also declined badly where toads are present.

Fertility control methods, though as yet unproven despite years of research, offer the only hope for control. However, I do not even know basic questions on this issue like how long poisonous toad eggs remain viable without sperm to fertilise them - I have assumed they would eventually die in the absence of sperm, but I have not found data.