8336 QUEENSLAND AGRICULTURAL JOURNAL. [1 May, 1902. 
tissue. In this young condition scores of insects may be met with in one of the 
situations mentioned, moving over the surfacelike so many large plantlice, even 
when the presence of the adults may be overlooked in consequence of their 
active habits. It is this insect that is the cause of the ‘‘ Maize Blight,” and of 
the great loss inseparable from its presence. This conclusion is the outcome 
of observations made during the course of the present visit to Ayr. Writing 
on some of the injurious insects of the maize plant in 1889, in which year the 
leaf hopper was first described’ (H. Tryon, “Insect and Fungus Pests,” pp 
193-6), this opinion did not, however, find favour. But then an opportunity 
for conducting investigations into the origin and nature of “ Maize Blight,” was 
not forthcoming. It was, however, stated then as follows:—“ It might be 
concluded that these insects give rise to all the symptoms of disease recorded, 
and especially so since they are both competent to, and do, injure the maize 
plant. We are not, however, prepared to admit as much concerning them, but 
only that they may act as the exciting cause of the ‘‘ Maize Disease. ”’ 
In giving rise to “Maize Blight,” the “delphax” insect does so primarily by 
oceasioning two descriptions of injury, one of which arises in the exercise of 
its feeding habit, and the other is attendant on the peculiar method observed 
by it in the deposition of its eggs. The latter mode of injury is, however, that 
which is by far the most potent in determining its presence. In the first place 
the insect feeds on the plant juices, or sap, and obtains this by inserting a long 
hair-like tube, formed by three conjoined portions, into its cell substance. 
This organ is found beneath the three-jointed proboscis proper, which, when 
the insect is not feeding, is bent backward, and is of a length sufficient to 
reach from the head to the hind body. When undisturbed and occurring upon 
its food-plant, it is almost continuously engaged in partaking of its liquid 
nutriment. In dealing with this leaf-hopper as the originator of “ blight,” its 
egg-laying habit is of especial significance. The eggs themselves are trans- 
parent, and when fully developed measure 56mm. (about ¢-line) in length, 
and are about three times as long as they are broad. They are placed by the 
arent insect within the tissue of the plant amongst the cells that intervene 
Soetemn the fibres (fibro-vascular bundles). Although there is usually no 
external indication of their presence, still they may occur in this situation in 
enormous numbers. They may be laid in almost any of the vegetative organs 
of the maize, except in the seed and essential parts of the flower. Commonly 
they are to be met with in the leaf-sheath, immediately beneath the inner skin 
or epidermis; also in the leaf blade itself, and again in the stem, and in the 
main stalk, as well as in the branches of the tassel or male inflorescence. 
When present in the last-mentioned situation their position may be revealed, 
on removing the gummy matter present, by the occurrence of minute elevations 
roughening the stem-surface. A small fragment of the plant may, indeed, 
contain a score or more eggs. 
In placing the eggs in the position referred to the insect utilises a peculiar 
instrument with which it is endowed. This is in the form of an elongated, 
slightly curved saw, the appearance of which is suggestive of the bread-knife 
that has recently found its way intomany households. This saw, together with 
its accesories, is contained in a conspicuous groove occupying nearly the entire 
length of the under surface of the abdomen. With it a tiny slit is produced, 
and into this, between two elongated directors, each egg on extrusion is forced. 
The saw itself is operated by four special muscles. Four or five eggs may be 
placed in each slit, but commonly only two or three, or even one. In almost 
all cases these minute slits remain open, and as, moreover, a determination of 
sap is occasioned by the irritating presence of the eggs within them, the latter 
finds its way to the surface, and hence the presence of sticky gum-like matter, 
formed on its evaporation, results. At the same time, but more especially on 
the issue of the insect-larvee, specks, spots, and blotches of yellowish-brown 
appear as evidence of the mechanical injury that has been inflicted. In 
addition to this, internal pathological changes arise within the tissue. These 
manifest themselves in the occurrence of small masses of froth-like matter 
