40 THE VICTORIAN NATURALIST. 



am inducei to hope that you will not turn a deaf ear to my request, but 

 that you will on this, as on former occasions, give us the benefit of your 

 I'iews. — Believe me to remain, yours faithfully, 



" F. Stanley Dobson. 

 " Professor M'Coy." 



" University, April 2S, 1884. 



" My Dear Dr. Dobson, — In answer to your invitation to suggest some 

 subjects of investigation for the next year's work of the Field Naturalists' 

 Club, of which you are president, I think the most interesting and useful 

 line of investigation not yet touched by the club, and yet particularly 

 suited to its functions, is the subject of the vegetable parasites belonging to 

 the class of insects, both native and introduced, which are injurious to cul- 

 tivated and native plants. The philoxera of the vine is so like the species 

 of other plants, that it is very important that members of the club travelling 

 much and observing in the field should endeavour to ascertain whether 

 other specie ; are in the country, and particularly to find out whether the P. 

 vastatrix attacks any other plant here, for if so, the destruction by the 

 state of vine3rards would have to be supplemented by other precautions. I 

 suggest this subject of research because I have collected a great deal of 

 evidence to prove that other imported parasites spread to plants of very 

 different species and genera to those to which such parasites are confined in 

 their own country. In one of the early decades of the Prodromus of tha 

 zoology of Victoria, I pointed out that the caterpillar of the Agarista 

 glycinfe, Avhich is a native insect, had left its native proper food, the 

 gnaphalium introalbum, to attack the foliage of the vine, doing immense 

 damage to the vineyards, although the plants are so dissimil;.r in all respects. 

 I would now suggest that the members should next j^ear determine as many 

 other similar cases as possible. Mr. Carson sent me some weevils last year, 

 collected from his apple trees, which he thought might be the American 

 apple weevil, which does such mischief in the United States as to be thought 

 worthy of a quarto illustrated memoir to itself ; but on examination I found 

 they were a native species, chiefly confined to the gum trees in the bush, 

 and it would be highly interesting if the members of the club would, hj 

 multiplied observations in the field, ascertain whether it has really acquired 

 the habits destructive to the apple of its American representative. Professor 

 Nanson sent me down a branch of an apple tree from Mount Maceion which 

 was showing signs of death, the cause of which I found was the multitude 

 of the mytilaspis covering the bark, specifically identical with that which 

 destroys the apple orchards in Europe and America ; and I now find it has 

 departed from its old-world habits, and commenced the destruction of 

 several difiierent species and genera of plants which it had not been known 

 to attack before. The commonest of our native species of Icerya I have 

 studied at the few opportunities I have for field work, ^vith one certain 

 result of very serious importance probably in the future — nanely, that it 

 brings forth young at every season of the year — for I find that it i.s now 

 leaving its native plants and attacking imported plants of the most dis- 

 similar character to its native jjroper food — fruit trees and large pine trees 

 being killed by it in my grounds at Brighton. To determine tlie list of 

 valuable imported plants which it now feeds on Avould be very useful and 

 interesting. Another point, concerning which the help of numerous 

 observers in the field is necessary to ascertain the precise fact, is the 

 determination of which precise species of ichneumon bores and destroys 

 each of the Coccidaj, or scale insects, which fortunately, we see, are perse- 

 cuted by native Hymenoptera, sometimes more than one species of ichneumon 

 boring one scale insect. I have been able to find only a few to establish 

 the fact with certainty, but the members of the club can work this field 

 advan tageously . 



Another nearly allied line of investigation, in which little has been 

 done in this country, specially requiring such an association as the club to 



