Plant Sanitation. 



140 



[August, 1909. 



That interpretation of the experiment 

 would involve the confusion of two 

 distinct theories, viz., (1) that all the 

 rubber formed is stored in the laticifer- 

 ous tissue and so " matures" there, and 

 (2) that the rubber formed at the age of 

 six is as " strong " as the rubber formed 

 at the age of eight. The experiment 

 proves that the first of these is, at least 

 in part, incorrect ; it gives no informal 

 tion whatever with regard to the second 



NOTES ON PARASITES OR INSECTS 

 THAT HAVE BEEN INTRODUCED 

 FROM FOREIGN COUNTRIES TO 

 CHECK OR EXTERMINATE 

 INJURIOUS INSECTS. 



Extracted from the Official Report on 

 Fruit, Fly and other Pests, 1907-8. 



W. W. Froggatt.) 



Parasites, and their Value and Limi- 

 tations in Controlling Injurious 

 Insects op the Garden and 

 Orchard. 

 One of the most interesting problems 

 in the study of economic entomology is 

 that of how far we can avail ourselves 

 of the services of predaceous or useful 

 insects that devour the injurious species, 

 by introducing them from other coun- 

 tries to check or exterminte in an arti- 

 ficial manner native pests, or foreign 

 accidentally-introduced ones that have 

 become pests in their adopted home. 



The subject is such a fascinating one, 

 that most people are apt to rush to con- 

 clusions before the matter has been in- 

 vestigated from all points of view. 



After many years' study in Australia, 

 both in the field and laboratories, 

 after information received personally 

 from entomologists, horticultural com- 

 missioners, orchardists, and inspectors 

 during my extended travels, and after 

 careful reading of the many reports, 

 bulletins, and newspaper cuttings issued, 

 1 propose to state my views on this pro- 

 blem, and shall quote in conclusion 

 the opinions of some of the leading 

 authorities on the question. 



It is a fact that, if it were not for the 

 countless millions of parasites (the majo- 

 rity of them so minute that their work 

 is never observed) which swarm in our 

 gardens and fields, there would be such 

 an overwhelming multitude of caterpil- 

 lars, grubs, aphides, and scale insects 

 at work, that there would not be a green 

 thing on the surface of the earth, 

 Nature in this abundance of natural 

 checks has provided for this balance of 

 power, and it is so maintained under the 



ordinary natural conditions of the native 

 forest and plains. Thus probably not 

 more than 5 per cent, of the millions of 

 eggs laid ever reach maturity and deve- 

 lop into the adult insect. 



From their size, colour, and activity 

 the fact that ladybird beetles were use- 

 ful insects was well known by entomo- 

 logists at a very early date, and in Kirby 

 and Spence's Entomology, published in 

 1816, the authors called attention to 

 the value of the common English lady- 

 bird beetle to the hopgrowers in devour- 

 ing their great pest, the hop aphis, in 

 the south of England. " If we could but 

 discover a mode of increasing these in- 

 sects at will, we might not only clear 

 our hot-houses of aphides by their means, 

 but render our crops of hops much more 

 certain than they now are." 



This is one of the earliest suggestions 

 made regarding the artificial production 

 of parasites. It is rather a significant 

 fact that though this ladybird (Cocci- 

 nella septempunctala) is often so abund- 

 ant in Kent that they are either blown 

 out to sea in such quantities that the 

 returning tide sweeps them up in long 

 ridges along the sea shore, or else they 

 cause quite a scare by SAvarming into 

 the houses in the summer time, yet the 

 hop aphis regularly occurs every few 

 years as a very serious pest. I, with 

 many of the leading entomologists of 

 the world, contend that, while we quite 

 recognise the importance of parasitic 

 insects in the work of keeping down 

 insect pests under natural conditions of 

 climate and cultivation in their own 

 land, yet we certainly dispute the state- 

 ments continually being made that every 

 pest (and they even proposed to cure 

 the bacterial disease "pear blight" in 

 California with a parasite) can be dealt 

 with by finding and introducing para- 

 sites from the country whence the pest 

 is supposed to have originated. 



If wishing for popularity, nothing 

 could be simpler than to advocate the 

 adoption of parasitic methods, for there 

 is a certain amount of plausibility in 

 the theory of introduced parasites to 

 eradicate all pests that appeals to in the 

 general public, who have not gone into 

 the why and the wherefore of the matter, 

 and particularly to the orchardist, who 

 naturally wishes to give up spraying 

 and fumigating, if he can simply turn 

 out a colony of parasites, sit back, and 

 they will do the work. As the results of 

 the parasite introductions become better 

 known, and the misstatements and 

 exaggerations with which they have been 

 surrounded are swept away, there will 

 be a revulsion of feeling, results credited 

 to parasites will be explained in other 

 ways, the introduced parasites will take 



