SCIENCE AND INDUSTRY. 
—<—<——$—— 
be transmitted by insects. One of the best known is Curly Leaf of 
the Sugar Beet, of which the chief insect that transmits the contagium 
is the Leaf Hopper—Mutettia tenella. California is endeavouring to 
control this insect by the use of parasites, and for that-purpose thon~ 
sands of Australian leaf hoppers of close relationship, which were 
found to be kept in natural control by native parasites here, were sent 
to California two to three years ago in order to breed out those para. 
sites for transfer to Hutettia tenella. 
Various species of aphids have been proved to act as disseminators- 
of such diseases as the mosaics of tobacco, tomato, sweet pea, sugar 
cane, cucumber, and bean. ; 
We have many examples of chloroses and mosaics in Australia, but 
to what extent any of them are infectious we do not know. They occur 
among such plants as the vine, apple, tomato, potato, bean, sweet pea, 
banana, and sugar cane. The usual practice is to treat the soil for 
some physical or chemical defect. Probably some of these chlorotic 
conditions will be found to be caused by a filterable virus, and the 
“Bunchy Top” disease of the banana in northern New South Wales 
and Queensland, as well as in Fiji and Ceylon, is one that might be 
investigated from this point of view. 
III. Inpirrecr Assocrarron. 
Insects are often indirectly associated with certain diseases by 
_ causing wounds, which act as entrance points for the infective prin- 
ciple brought there by some other agency. How often do we come 
across tle term “wound parasite” in the text-books on plant pathology? 
The Melanconium fungus, or Rind disease of sugar cane, 18 stated to 
be a wound parasite, Cobb claiming that stem-boring beetles and leaf 
hoppers are the cause of the wounds. 
Among bacterial diseases the angular leaf spot of the cotton (Bm. 
malvacearum) in the United States of America is caused by the entrance 
of germs into leaf injuries by Jassids. The disease is not recorded for 
Australia. i : 
It will be seen that the work of insect transmission of 
disease demands the co-operation of the pathologist and the entomolo- 
gist. It will be necessary to work out the habits and the anatomy of 
the insects, and even to breed disease-free insects to act as controls in 
experimental work. The whole course of the organism on or through 
the insect, the question of the transmission of infection to the offspring, 
the length of time that virulence is maintained in the insect or after 
passing through the insect, and the number of generations that may | 
be infected, will all require careful determination. How soon after 
taking up an infective principle is transmission of the disease possible, 
"what is the exact method of transmission (by bite, feces, &e.), and from 
What parts of the insects (e.g., salivary glands, crop, &c.) can the con- 
tagium be derived, are some of the problems that require solution, and 
will ‘demand careful experimental work by well-trained investigators, 
working in co-operation. When will Australia profit by the lessons 
so plainly given by the United States? ; , 
e 
658 
