RELATION OF INSECTS TO DISSEMINATION OF DISEASES. 
Smith, using the Colorado Potato Beetle. We have not yet found the 
Apple and Pear Blight in Australia, but the Potato Wilt (B. solana- — 
cearum) and the cabbage Black Rot (due to Bm. campestre) occur here. 
The latter has been proved to be transmitted by various plant bugs, 
beetles, aphids, and insect larvee, that feed on cruciferous plants. 
Among diseases of animals, some of the parasitic Trypanosomes 
are mechanically carried by blood-sucking insects, and transferred 
directly to vertebrate hosts without having undergone any change. 
Fungous Diseases—The Brown Rot of stone fruits (Sclerotinia) is 
spread by wasps, soldier bugs, and other insects puncturing fruit. Suck- 
ing insects of the squash bug family (Coreidw) are known to puncture 
fruit, and so pick up and distribute the spores of the fungus. The 
Black Spot of cabbage (Phoma oleracea) is commonly disseminated 
through injuries caused by wire worms. <A disease which Massee states 
has been spread greatly in England by the Woolly Aphis (Schizoneura 
lanigera) is the Nectria ditissimau canker on apple trees.. He goes so 
far as to say that had there been no woolly aphis there might not have 
been any canker. Our experience is somewhat different. We have any 
quantity of woolly aphis in Australia, but as yet there is no record of the. 
Nectria disease, though several other cankers are known. Nectria occurs 
in New Zealand. 
In the case of anthracnose of sweet peas, circumstantial evidence 
points to aphids and red spiders as common distributors of this disease. 
In some parts of New South Wales, Colletotrichum on*garden peas has 
been disastrous to the crops, but these epidemics have not been materially 
widened by insect transmission. 
» I. Mecwanicatry Carrtiep. 
(b) Accidental Infection without Direct I noculation. 
The insect is a mechanical carrier only, and the infective organism - 
is not directly inoculated, but is accidentally sown from the insect’s 
body. 
Bacterial_—In human diseases, house flies are common agents of dis- 
Semination in this manner. Their legs and body are hairy and well 
adapted for mechanical carriage of bacteria which they pick up when 
they come in contact with infected material. Outbreaks of typhoid and 
cholera have frequently been traced to flies as the active agents. ' 
Similarly in plant diseases, various flies often carry the sap of 
diseased pomaceous trees after pruning, and spread B. amylovorus to 
healthy trees. Ants act in a similar way. Hail-marks form entrance 
points for infection. 
Walnut Blight occurs in several localities in Australia, and is ap- 
parently spreading. In California, R. E. Smith isolated the causal 
organism Pseudomonas juglandis from the bodies of flies, which had 
been attracted by the exuding organic matter. 
Fungous Diseases—Many rust spores are carried by insects which 
are attracted by the bright colour, odour, and exuding sweet fluids at 
Various stages of development. Johnson, in United States of America, 
working on floret sterlity of wheat, found thrips were often numerous 
655 
