April, 1921. 



SCIENTIFIC AGRICULTURE 



Entomogenous Fungi 



By ALAN G. DUSTAN. 



Assistant Entomologist, Dominion Entomological 



Laboratory, Fredericton, N.B. 



167 



In carrying on investigational work, especially 

 where an outbreak is severe, the ontomolog-Lst often 

 finds that many of the insects under observation are 

 killed by an unknown disease. The insects so affected 

 often assume weird and unnatural shapes, become hard 

 and mummified and in many cases are covered with a 

 white growth. Closer observation shows that this con- 

 dition (has been brought about by a fungus which has 

 gained access to the body of the insect where it has 

 developed at the expense of the softer tissues. 



These fungous diseases, known teehnicall}^ as ento- 

 mogenous fungi, have been recognized for a great num- 

 ber of years but it is not until comparatively recently 

 that they have been considered of importance from an 

 economic standpoint. Previously they were looked 

 upon merely as interesting biologiciil phenomena, but 

 today it is known that the.y may be often used with 

 great effectiveness in combatting many insect jieKts. 

 The work of these fungi in a great number of cases has 

 been grossly exaggerated but in numerous instances 

 such diseases have played a very important part in con- 

 trolling some of our severest outbreaks. 



Unfortunately, however, these fun,i;i will not grow in 

 all countries nor at all seasons of the year, and as a 

 result many attempts to use and artificially spread en- 

 tomogenous fungi have been uiisuecessful. Like other 

 types of fungi they prefer a warm, moist climate, with 

 plenty of rainfall and a high relative humidity. In hot, 

 dry weather they cease to gro^v and in many cases 

 form resting spores to carry them over such unfavour- 

 able seasons. 



In regard to the hosts or insects which they attack, 

 entomogenous fungi do not always show much dis- 

 crimination. Some diseases have been recorded as at- 

 tacking only one species of insect host. In other cases 

 the same fungus may be found on a number of genera 

 in a certain family. And in certain instances one spe- 

 cies of fungus will attack insects in seven or eight 

 orders. As an example of this last type I might in- 

 stance the common insect fungus, Entonwphthora 

 sphacroxpermn, which has been found growing on re- 

 presentatives of the following ordei's: Lepidoptera, 

 Hymenoptera, Diptera, Coleoptera, Hemiptera, Neurop- 

 tera and Thysanoptera. 



The liability to infection by these fungous diseases 

 is shared alike by larvae and pupae -and in certain 

 cases even the adults are known to be attacked. It is 

 in the immature stages, however, that insects are most 

 susceptible, although in certain orders, notably Lepi- 

 doptera, the occurrence of disease among the adults is 

 not uncommon. 



Looked at from a purely l)i('logical standiioint, the 

 work of (utomogenoiis fungi is a most interesting 

 phenomenon ; but viewed in the light of an important 

 control factor, the mycoentomogist sees in these fungi 

 a possible ally which may be used to help him fight in- 

 sect outbreaks with the minimum amount of labour and 

 cost. For the last forty years experiments have been 

 carried on all over the civilized world to test out the 

 work of these fungi and to see if they can be spread 

 artificially or not. In most cases the results have been 



disappointing but in some cases the efforts of the in- 

 vestigators have been crowned with great success. 

 From the viewpoint of the practical mycoentoraologist, 

 .however, no matter how interesting a fungus may be, 

 it is of little use if it is not amenable to cultural 

 methods and artificial dissemination among the insects 

 he wishes to control. 



Early Work With Fungi. 



The first description of an entomogenous fungus was 

 written in 1754 by Father Torrubia. The insect in 

 question was a wasp collected in Havana and attacked 

 by what i.s now thought to be a species of Cordijccps. 

 Of course, previous to this time fungous diseases grow- 

 ing on insects had undoubtedly been noted, but this is 

 the first authentic case where a disease was actually 

 studied and described. From that time onward this 

 subject gradually began to attract the attention of 

 scientists and scattered through the older literatirre we 

 find accounts and popular descriptions of these fungi. 



It was not till 1880, however, over a hundred years 

 after the time of Father Torrubia, that entomologists 

 conceived the idea of making use of these fungi to help 

 them in fighting insect outbreaks. From Russia comes 

 the first record of work done in connection with the 

 artificial use of entomogenous fungi. In 1880, Met- 

 schenikoff found that the cockchafer of wiheat and a 

 sugar beet curculio were both susceptible to a disease 

 commonly known as the "Green Muscardine. " His 

 infection experiments with the cockchafer were only 

 in part successful but the same experiments with the 

 curculio were very successful. A little later (1888) 

 another Russian entomologist carried on a similar set 

 of experiments with the same disease and was success- 

 ful in bringing about an eighty per cent mortality 

 among the curculios. 



The success of the Russian scientists was infectious 

 and within a very few years experiments with entomo- 

 genous fungi were being carried on in many countries. 

 As a result we find that today this subject is attracting 

 the attention of entomologists in various parts of 

 the United States, in Hawaii, South Africa, South 

 America, and to a lesser extent, in most of the other 

 civilized countries. 



Systema,tic Position of Entomogenous Fungi 



Entomogenous plants in general may be divided 

 into three main groups. First, the bacterial foi-ms which 

 produce diseases in insects; second, the entopliytous 

 algae; and thirdly, the fmigi which are parasitic on in- 

 sects. Of these three only the last-mentioned will be 

 considered under this heading. 



Entomogenous fungi can be roughly grouped into 

 three classes, according to the type of spores they pro- 

 duce. The first group includes those forms which are 

 characterized by the production of zj'gospores and 

 azygospores and is represented by the family Ento- 

 mnphthoraceae. In the second group we find those 

 fungi tlhat have their sexual spores bom in an ascus, 

 known as ascispores and included in the order As- 

 comyeetales. In tbe last group are found those fungi 

 which of necessity are classified with the Fungi Im- 

 perfecti, on account of the fact that only part of their 



