382 



THE AGRICULTURAL NEWS. 



December 1, 1917. 



STORY OF AN EFFORT TO INTRODUCE 

 USEFUL PARASITES. 



Under the heading Biological Studies applied to Agricul- 

 ture in the last issue cr this Journal, reference was made to 

 the White Fly of Florida {Aleuro<:ks citri), its ravages among 

 the citrus plantations of that State, and the marked degree of 

 success in controlling its attacks which resulted from 

 cultivating and disseminating certain fungi parasitic on 

 this scale insect. The means of control of the technical kind 

 have also been found useful, notably the fumigation of trees 

 effected with hydrocyanic fumes, and also the spraying of them 

 with chemical insecticides, but both of these need to be 

 frequently repeated, and are expensive. 



In the account of M Marcbal's scientific visit to the 

 United States, from which the article referred to was for the 

 most part translated, there is given a very vivid and interesting 

 story of an attempt made by the orange planters and Govern- 

 ment of Florida, with the co-operation of the Bureau of 

 Plant Industry, to obtain and acclimatize other parasite.s, 

 especially insects, which might prove an even more efficient 

 control than the means hitherto adopted. This story is 



■worth teliii]g as an example not only of the perseverance 

 which the scientific men of the United States devote to 

 a question of research, but also of the almost unlimited 

 means placed at their disposal by an enlightened Government 

 and an intelligent community in order to attain the end 

 •aimed at. 



Ahurodes citri or White Fly is a heraipterous insect, 

 closely allied to the Coccids or true scale insects. Of Asiatic 

 origin, it began to be noticed in Florida about the year 1879, 

 and was almost immediately recognized as one of the worst 

 eneraie.-i of orange and lemon trees. A great reason for its 

 rapid spread in the Southern States is that it can live on 

 many other plants besides those of the citrus family, among 

 which are several indigenous to that region. It accordingly 

 spread through all the States bordering the gulf of 

 Mexico, and before very long made its appearance in 

 Californian citrus orchards also. Ballou, in 'Insect Pests of 

 the Lesser Antilles', says that Akurodes citri, though ocur- 

 ring in these islands is not a serious pest. He questions 

 -whether the species may not rather be A. nuldfera. 



The damage it eausfs to the trees in reduction of yield has 

 been estimated at not less than §.500,000 in one year in the 

 State of Florida alone. The damage is not only the result 

 of the punctures made in the tissues of the leaves by the 

 insect in order to extract the sap, but is also inten.'^ified by the 

 fact that the insect causes the development of a .sooty mould 

 on the leaves and fruit of trees attacked, which interferes 

 ■with the respiratory functions of those organs. The difficulty 

 experienced in effectually controlling this pest arises, not 

 from any special power of resistance which it posesfes against 

 chemical insecticides, for this is relatively feeble, but from its 

 immense fecundity. It is computed that there are three 

 generations in the year, and that each matured female lays 

 from 100 to 250 eggs. Thus, in spite of efficacious spray- 

 ing or fumigating, some few individuals must escape, 

 and however few, they are ouite enough to produce at the 

 end of two or three generatons a s: fficiently numerous 

 j,rogeny to become again a menace to the citrus crop. 



Seeing that the natural enemits of the Aleurodes in 

 Florida were not sufficient to check the devastations of 

 tl.e pest, and considering that undoubtedly it had been 

 introduced from the East, there arose a strong public 

 < pinion among the citrus planters of Florida that the best 

 course to pursue would be to .search in its original habitat 

 for parasites on this pest, and to take steps to acclimatize 



them in Florida. After some correspondence between the- 

 orange growers, the Biireau of Insect Pests at Washington, 

 and the Experimental Station of Florida, the matter was 

 placed before Congress, who pissed a vote, allocating 

 a special sum for research as to the original habitat of 

 Aleurodes citri, for collecting any natural enemies of this 

 insect, and for the acclimatization of them in Florida. 



Mr. R. S. Woglum, one of the Entomologists on the 

 Staff of the Bureau of Insect Pests was appointed to 

 undertake this task. He left New York on July 31, 

 1910, and visited the citrus cultivations of Spain, Italy, 

 and Sicily without fi.nding any trace of Aleurodes citri 

 or its parasites. He then proceeded to Ceylon, where 

 again he could find no presence of this destructive insect. 

 From Ceylon he went to Calcutta, and there in the Museum 

 of Natural History he found specimens of orange leaves 

 covered with Aleurodes citri, the Ubel attached to them 

 showing that they had been collected in the Himalayan region 

 to the north-west. 



Mr. Woglum immediately set out for this region, and at 

 Saharanpur he found numerous orante trees with Aleurodes 

 on them. The.se were, however, very scattered, and this 

 presumed the presence of natural enemies. Soon after 

 Mr. Woglum discovered some lady-bird beetles which fed oa 

 the Aleurodes both in the larval and adult stage. He sent 

 two consignments of these lady-birds to Florida, packed in 

 the best way he knew, but not one oi them survived to reach 

 Florida. 



While in the neighbourhood of Lahore, Mr. Wooflum 

 obtained observations on, and specimens of, a small wasp 

 (Prospaltclla lahoren%is) which preyed upon Aleurodes citri. 

 Mr. Woglum had thus accomplished the first part of his 

 mission. How to collect, convey to Florida, and acclim- 

 atize these helpful parasites, was the next question. 



It was necessary to transport orange plants in full leaf, 

 inl'ested with Aleurodes, in order thus to provide food for the 

 beneficent paia^ites on the voyage, which would take ffom 

 India to Florida from five to s-ix weeks. Mr. Woglum in 

 the spring planted in pots orange plants from one to 4 feet 

 hifh; then in September he placed them under orange trees 

 infested with Aleurodes. Naturally the orange plants in the 

 pots were soon badly infested. Not long after, the parasitic 

 lady-bird and wasp made their appearance among the potted 

 plants, and attacked their prey the Aleurodes. About the 

 middle of October Mr. Woglum thought that it would be 

 good to ship his young orange trees, covered with Aleurodes 

 infested in turn with the larvae of the parasitic lady- bird 

 and wasp, to Florida. Packed in Wardian cases the plants 

 made a successful journey of six weeks durati"n from Lahore 

 to Florida. So scientific and successful were tlu^ arrange- 

 ments that a number of the predatory lady-birds and wasps 

 were received alive at the entomological station of Orlando, 

 Florida. 



Unfortunately the climatic conditions in India at the 

 season of shipment and those in Florida at the time of 

 arrival did not coincide. These allies in the Florida war 

 against Aleurodes arrived in Florida just when the foe was 

 resting for the winter in the pupal form, in which it was not 

 attacked by either of these allies, which attack only, either 

 the larval form, or the egg. In consequence, before the next 

 spring, all the predatory insects imported from India had 

 perished from want of their prey. 



This may seem as if nmch of the work in the direction of 

 importation and acclimatization of benelicial insects was 

 doomed to failure. These facts, however, only show that 

 there is need for immense labour and care, 



