ENTOMOPHTHORA 157 



FUNGI AND BACTERIA. 



Thaxter has recorded attacks on adult mosquitoes by the fungus known as 

 Entomophthora splKsrospenna. It reaches Diptera generally, but is especially 

 noticeable with the mosquitoes. Another fungus (Empusa culicis) also destroys 

 mosquitoes in both Europe and America. Thaxter also states that Empusa 

 papillata destroys small gnats (probably mosquitoes among them) . The eggs of 

 Psorophora howardii were found in the summer of 1901 to be covered with a 

 fungous growth which has been determined by Mrs. F. W. Patterson, of the U. 

 S. Department of Agriculture, to belong to the genus Polyscytalum. 



A most interesting instance of the destruction of mosquitoes by Entomoph- 

 thora is described by Mr. E. H. Pettit in Special Bulletin N"o. 17 of the Michigan 

 Agricultural Experiment Station (see pi. VII, fig. 2). 



" On August 5, Mr. Barlow found a number of adult mosquitoes killed by a 

 fungus, Entomophthora sp. nov. They were very numerous on the margins of 

 one of the pools in the north woods, sometimes almost covering the soil and the 

 pieces of bark to which they clung. Some were just killed and showed little, if 

 any, external growth, and some vv^ere covered with a dense dull white growth. 

 All were within a few inches of the water and all faced away from it. Imagine 

 thousands of mosquitoes all headed away from the water as if they were trying 

 to get away from it. 



" It would seem that the effect of the disease is to draw the affected insects 

 to the water, possibly by creating a thirst, after slaking which the insects, in 

 trying to retreat, are caught and stopped in their course by numerous rhizoids 

 or anchor ropes which are sent out by the fungus in the body to fasten the victim 

 permanently to the place where its ill luck overtakes it. Unfortunately for the 

 mosquito host, the diseased individuals die just in the right place to infect their 

 fellows as they go to the pool to drink or to lay eggs. This is a case where the 

 fungus seems to influence the host in such a way as to lead to the spread of the 

 disease. Similar impulses seem to be induced in the case of other species — the 

 Sporotrichum that is used against chinch-bugs seems to impel the diseased in- 

 dividuals to hide under clods or in other moist and protected places, just the 

 places where the young bugs come to shed their skins or to molt. This is of 

 course the best possible way to spread the disease. Then, too, in the case of the 

 common grasshopper disease, Empusa grylli, the dying hoppers are impelled to 

 climb to the tops of weeds and plants, and as the fungus throws its spores to some 

 distance, there is a good chance that some of them will fall on the bodies of other 

 grasshoppers. 



" The appearance of the mosquito fungus is quite characteristic. The entire 

 body is swollen and covered with a dull white growth, sometimes almost 

 plumbeus. The body is fastened down by many slender brownish ropes. A 

 microscopic examination shows the growth to be made up of fine threads 

 (mycelium) bearing spores at their distal extremities. These threads are 

 usually simple, though sometimes bearing a few short branches. They are 

 septate at long intervals, granular, and contain vacuoles. The spores are lunate, 

 bluntly rounded at both ends. In size they measure about 50 microns long by 

 13 in diameter, some being as long as 55 microns and a few as short as 28 

 microns. They are finely granular, with oil globules usually near the ends. In 

 a single specimen large numbers of resting spores were found. In this case the 

 mycelium had largely disappeared. The resting spores were spherical, hyaline, 

 with many small translucent interior globules. They measured from 40 to 44 

 microns in diameter. 



