To Charles Riley   21 March 1887

Melbourne,

21 May 1887.¹

C. V. Riley Esqr,

Entomologist to the Department of Agriculture,

Washington

In reply to your letter of the 15th December,² dear Mr Riley, I beg to inform you, that the Icerya Purchasi, (or a closely alied species) altho occurring on Acacia mollissima and some congeners in the colony Victoria, has not attacked here, (so far as I can learn or had occasion to observe) destructively the Orange-Orchards. I will however make further enquiries as well in this colony as in New South Wales, South Australia, New Zealand, and let you know the result.

Possibly the Icerya develops more readily in a moister clime than that of Victoria, and thus becomes more mischievous in California than here.

The introduction of this destructive insect into your states by means of Acacias seems to me very unlikely, because the various species of Acacias are so easily raised from seeds, that no one will think to introduce them by living plants. Moreover it could not have been the Acacia latifolia, which was the host of the Icerya because that species is a native solely of the North-Coast of Australia and as yet nowhere existing in horticulture. Acacia armata certainly is grown for hedges, but always raised from seeds, chiefly obtained from South-Australia. It seems therefore more likely, that when Acacias are grown anywhere, they would afford — particularly in humid climes, — a favorable opportunity for the Icerya to spread. A similar circumstance occurred in Ceylon and an other in some parts of Brazil, where an indigenous insect-plague became aggravated, when Eucalypts, on which that insect preferentially seized, became reared always from seed. Whether the Icerya was originally an inhabitant of Victoria or merely immigrated, I will endeavour to ascertain; but such a subject of inquiry is surrounded with difficulty now after half a century's existence of the colony, particularly as the Icerya drew no attention here by any extensively injurious effects on any cultural plants, though it may have caused on some places minor or transient injury. Allow me, honored Sir, to congratulate you to your recovery from a long and severe illness, and let me express a hope, that your grand talent and unrivalled experience will long advance science yet and rural industries.

Regardfully your

Ferd. von Mueller

Acacia armata

Acacia latifolia

Acacia mollissima

Eucalyptus