1 Dec., 1897.] QUEENSLAND AGRICULTURAL JOURNAL. 465 
Entomology. 
INSECT FRIENDS AND INSECT FOES. 
[Read at the Conference of Australasian Fruitgrowers—Brisbane, June, 1897.] 
By HENRY TRYON, 
Government Entomologist. 
2 
‘ 
Tur importance of studying the relations that subsist between insects and plants 
that are the objects of the fruitgrowers’ care, and between one class and another in 
so far also as they affect his interest, is so obvious that it would but insult the 
intelligence of those present were any attempt made to specially urge the claims of 
such a subject—as may be deemed to be embraced in the title of this paper—on your 
consideration. 2 
Insrcr Fors. 
With regard to those insects that may be defined by the term “ foes,’ it may be 
remarked that it is pr»posed to treat the subject in a general manner without special 
reference to any particular plant-pest, since the able Government Entomologist of 
Victoria (Mr. C. French) has graciously offered to address you on this topic, and it 
would not become the writer, even were he disposed to do so, to endeavour to antici- 
pate any of the important discoveries that doubtless so competent an investigator has 
to announce. 
Prompt Measures—Rate of Ivcrease of Insects.—The apparently sudden appear- 
ance of an insect pest ina place where its presence has never previously been remarked 
and its speedy dissemination through a district, are occurrences not infrequently met 
with. The explanation of the phenomena, however, is seldom forthcoming; and yet 
it resides to a great extent in facts pertaining to the insect itself and its develoment. 
The case of the Aphis is significant in this connection. Charles Bonnet* has 
informed us that, with a particular species under his observation, single females 
produce generally each 90 young ones; at the second generation these 90. produce 
8,100; these give a third generation that amounts to 729,000 insects; these in their 
turn become 65,610,000; the fifth generation, consisting of 590,490,000, will yield a 
progeny of 53,140,106,000; at the seventh we shall thus have 4,782,789,000,000, and. 
the eighth will give 441,461,010,0( 0,000. ‘This immense number increases innumer- 
ably when there are eleven generations in the course of the year. Moreover, as the 
writer has elsewhere observed, “ the rapidity with which generation succeeds genera- 
tion, may be inferred from the fact that on examining a viviparous female not only 
can one see within it the young unborn insects, but even within the latter themselves 
the members of a succeeding generation.” t 
The fecundity of the Aphis is, however, exceptional; but still there is a high rate 
of increase in other insects also. Amongst Scale Insects, perhaps, there is none that 
has ever created such general interest as has the San José or Pernicious Scale 
(Aspidiotus perniciosus), an interest in which many of the fruitgrowers of the Aus. 
tralian colonies have amongst others participated. In New Jersey, U.S.A., where 
its reproduction is necessarily restricted to the summer months, the female insect 
becomes adult in about thirty days; reproduction then ensues, during which from 
480 to 500 young are born. But before it has ceased to reproduce, its progeny has 
commenced also to multiply. ‘hus nearly five full broods arise in the course of the 
season, and so the descendants of a single female may reach the enormous figure of 
1,608,040,200.f 
As a further instance may be taken the Boll Worm (Aletia argillacea, Hubnr.) 
of the cotton plant, of which the female lays 500 eggs. In its case, according to EH. 
A. Schwarz, there may be seven, and are probably more, generations in a season. 
* Traité d’Insectologie, ou Observations sur les Pucerons, pp. 28-38. Paris, 1745. 
+ “Insect and Fungus Pests,” p. 85. Brisbane, 1889. 
t J. B. Smith. Report of Ent. Dep. 1896, Agr. Col. Exp. Stat. New Jersey, pp. 542-3, 1897. 
