168 



SCIENTIFIC agriculturp: 



April, 1921. 



Green Apple Bugs 



Attacked by a Fungous disease 



(Photo by L. G. Saunders). 



life-history is known. The most of the last class are 

 supposed to belong- to the second group ,the aseus-bear- 

 ing fungi, but are placed temporarily in the Fungi Im- 

 perfec'ti luitil more is known of t.iieir ascigerous -tagc, 

 without wjiich knowledge they eannot be ela-sified. 



Life History of a Typical Entomophthora. 



Infection anicmg ciitonnigciKiu.s rungi results, in must 

 cases, from contact with a conidial spore which, adher- 

 ing to the insect host, enters its body b.v means of a ger- 

 minating hypha or tube. Although this process has 

 never yet been actually seen, it is generally supposed 

 that the hypha penetrates the insect's body at some 

 point where the integument is less highly developed, 

 as, for instance, between the body segments or joints of 

 the legs or perhaps directl.v throngb the stigmata. It 

 has also been proven that in some cases infection re- 

 sults when the spores are taken directly into the 

 stomach with the food, but this method is not so com- 

 mon as the one firsit mentioned. 



After the hypha of germination has entered the host 

 it grows and develops at the expense, first of the softer 

 tissues but latei- of those parts more highly chitinized. 

 Many authors think that fungi have the power of 



secreting some li((uid wliich acts on the body tissues of 

 the host and helps to break them down and convert 

 them into food for the developing plant. This is prob- 

 ably a fact, for it could onlj^ be through the agency of 

 such a digesting secretion that the fungus would be 

 able to break down the harder tissues as it does. 



In growing, the fungus does not usually form a 

 threadlike, branched mycelium, but multiplies by 

 means of what is known as hyphal bodies. Those hy- 

 |)lial bodies are .short, thick fragments of the plant: of 

 varying size and shape, which grow by means of bud- 

 ding, and in many cases look in<e yeast cells. They are 

 found first in the blood stream of the host, but as they 

 increase they penetrate every part of the body and 

 when the tissues are all consumed and the insect finally 

 dies, the exo-skeleton is found to be entirely filled with 

 them. Should conditions at this stage become un- 

 favourable for further growth, these hyphal bodies be- 

 come rounded up, surround themselves with a heavy 

 cell wall and become resting or chlamydospores, in 

 which condition they are able to remain for long 

 periods of time. 



Under more favourable conditions, however, the fun- 

 gus proceeds to complete its growth and each one of 



Opionectria coccicola. 



The white-headed fungus of 

 purple scale. 



Sphaerostilbe coccophila. 



The red-headed fungus 



of San Jose scale. 



these resting spores germinates and sends out a deli- 

 cate hj'phal ti;be. The germination of this elila my do- 

 spore results in the formation of either sexual or asex- 

 ual resting spores, or of conidiophores bearing conidia. 

 If conidia are to be formed, the germinating tubes grow 

 rapidly upward and burst through the thinner and 

 softer parts of the insect's body. Sometimes they are 

 branched, but in the simplest forms they grow upright 

 as simple, unbranched conidiophores. At the extreme 

 tip of these upright hyphae the conidia or spores are 

 borne and when mature the.v are shot off into the air 

 with amazing force, where they float around until they 

 come in contact with a suitable insect host. This they 

 adhere to b.y means of a sticky substance with which 

 they are surrounded, and at once send out a germinat- 

 ing tube which enters the body of the insect, as already 

 described. Should the conidia alight on a substance 

 unsuited to its development, secondary conidia are 

 formed and in tuni .shot off into the air in the hope of 

 reaching a more favourable food supply. These second- 

 ary conidia are formed from the primary ones in a very 



