126 



THE AGRICULTURAL NEWS. 



April 10, 1915. 



FUNGUS NOTES. 



THE EFFICIENCY OF FUNGOID PARA- 

 SITES OF SCALE INSECTS. 

 II 



II. i ae oi we ithei condil 



on the ' "i scale-destroying Fungi, there 



remains to bi the o lestion as to how Far theii 



efficiency i ti be increased bj artificial distribution. As 

 a consequence of the success since shown to be due to verj 

 special circuin inci of the introduction oi Australian ladj 

 bird beetles into California to prej on the cottony cushion 



I : hi has been given ti i the 

 question of natural enemies "f injurious insects. The 

 results have been usually disappointing, Imt the rules of the 

 game are aovi pretty clear, The rapid increase of a pest 

 which may take place when it is newly introduced into 

 a country where natural enemies adapted to destroy il are 

 few or absent, may be checked in some cases by bringing in 

 such ciit]iii>- from countries where they exist. To use 

 :i relevant illustration should some kind of white tl\ become 

 troublesome in the West [ndies, it would be worth whili 

 introduce the fungi which are parasitic on certain species in 

 Florida, in the hope of their exercising a check on the insect 

 in these islands. Were the experiment successful, the control 

 might be more efficient or less si i than it is in Florida, accord 

 ing to the extent to which the conditions favoured the fungi. 

 It would not be expected to be complete. The point is, that 

 once given a start, the fungus parasites might establish them- 

 selves and constitute permanent factors modifying the activity 



of the insect. 



When such a factor is already well established in 

 a country, and it is desired to increase its effect, the element 

 of artificiality becomes much greater. The fungus (and the 

 same applies to other parasites) already has its place, its 

 settled lines of action, so to speak, Bj cultivating it, by 

 distributing it, it may be increased for the time, but when 

 such means are no longer used it will settle back to much its 

 old position, which is determined by natural conditions and 

 changes only in response to their fluctuations. This has 

 been and is the situation with regard to most work on the 

 fungus control of insects. 



The method has an insidious appeal, in that it seems to 

 promise to the planter a self acting remedy, but experience 

 shows that, as might have been expected, result.- are not 

 to be obtained without an adequate amount of trouble. 



The use of the fungi does afford an alternative to the 



employment ol pojb us sprays, but save that in the one case 



a living organism is used, one method is as artificial as the 

 other, and it depends entirely on the particular circumstances 

 of the case as to which is more efficienl oi less troublesome. 

 That is a question foi the entomologist and foi the planter. In 

 Florida, in connexion with white fly control, each method has 

 its advocates. In Trinidad, where periodic dusting with Fung 

 spore- is in use against froghopper on sugar-cane, it would 

 hat spraying with insecticides is out of the question. 



In one !,■ pect the v ' ol fungi has a disadvantage as com 



pared with the useof poisons. The latter \ be applied with 



advantage at the beginning oi an attack, the former do not 



bei ii vi n i istg are plentiful. Like all 



Fatal parasites, the} tend to cut theii own throats. The re 



thoroughly they kill off 1 the les material thej have 



to live uj When the chances of infect ieen thus 



redu ' or colonists from another ai 



star wave of insect infestation, which in time is 



overtaken by the rising numbers of the parasite. 

 This succession i- perhaps most easily seen in the West 

 [ndies in the action of the shield-scale fungus working on 

 more or less isolated tree-. In lime plantations it takes 

 place in sections ol the cultivati.ni rather than on individual 



trees. 



Several observers agree thai in the case of white fly 

 ml in Florida, the parasites undei >le conditions, 



ami without artificial aid become effective aboi every third 



year. 



It was point' d out in the first part of this article that in 

 ts among the Lessei Antilles, conditions are so 



Mi-able to the -pread of scale fungi that the matter 



may be let' to itself. What can be done in the districts 



no! bo favoured? Cnless there i- at some period of the year 



n when the fungi, if thej :. can be observed 



to become active, it is not worth while to trouble about 

 them, [f they are not present at all, it is at least possible, 



since they are so well distributed through the i-l amis, that 

 the conditions are not favourable. Where they have a pi nod 

 of valuable activity in the wet season, followed l>\ compar- 

 ative scarcity in the dry, something maj be done. It will be 



found that while they disappear from view in exposed 

 situations, they continue a visible existence in damp and 

 sheltered places. The spores of i t of our species do not 



appear to be very resistant, and it is probable that it is from 

 such places that the -pread begins when condition- become 

 Favourable. By distributing the material thus available, or 

 by taking material from the earliest plant- to become infested, 

 it is probable, and has often been definitely claimed, that the 

 progress of the fungus may be considerably hastened. 

 Especially is this the case with i.-olated trees. 



Various methods are available in making useof such 

 material. Branches from the fungus-infested tree may be 

 tied among the leaves of the tree to be infected. Leaves 

 bearing the fungus may be dipped in water and rubbed on the 

 leaves bearing the scales,, or pinned in contact with them. 

 The material may bestirred up in water to wash off the 

 -pores, or ground up and mixed with water in the case of 

 leaves. 



This mixture may be sprinkled on to the trees 

 with a brush, or the twigs bent down and dipped into it, or 

 it may be applied with a syringe or other type of sprayer 

 after being strained through a wire sieve, (.'loth strainers 

 keep back the spores. Brass or copper sprayers may be used 

 if they are idem and the material is not allowed to stand very 

 long in the tank. 



Comparative trials of these methods have not been 

 made in the case of the West Indian species. Drs. .Morrill 

 and Back (Natural Control of White Flies in Florida: Bull. 

 102, Bur. or Entom., 1912) favour the spore-spraying method 

 tor distributing the Aschersonias there concerned. 



The condition of the material used Would appear to 



have more influence on successful introduction than the 

 method of it- application. Ii should In used a- fresh as 

 possible, and in the active spore-producing stage, recogniz- 

 able mi examination with a pocket lens. In the case ol 

 the shield -cale fungus, a powderj glistening appearance 

 denotes the presence of the -pore-. In the red and white 

 headed fungi, the loose tufts ol ripi spores can be easily 



made out 



The common occurrence of such fungi on potted plants 



ists thai the., might in some cases be used with 



advantage. When a branch or twig is tied int the 



immersion oi tin cut end in watei contained in a narrow 



necked bottle j, ,, obvious benefit. 



