

INSECTS IN RELATION TO PLANTS 



217 



digests the softer portions of the insects, and the dissolved nitrogenous 

 ; matter is absorbed into the plant. Utricularia has little bladders which 

 entrap small aquatic insects. These plants are only partially dependent 

 on insect-food, however, for they all possess chlorophyll. 



Bacteria cause epidemic diseases among insects, as in the flacherie 

 of the silkworm; and fungi of a few groups are spe- 

 cially adapted to develop in the bodies of living 

 insects. 



Those who rear insects know how frequently 

 caterpillars and other larvae are destroyed by fungi 

 that give the insects a powdered appearance. These 

 fungi, referred to the genus Isaria, are in some cases 

 known to be asexual stages of forms of Cordyceps, 

 which forms appear from the bodies of various larvae, 

 pupae and imagines as long, conspicuous, fructifying 

 sprouts (Fig. 254). 



The chief fungous parasites of insects belong to 

 the large family Entomophthoraceae, represented by 

 the common Empusa muscce (Fig. 255) which affects 

 various flies. In autumn, especially in warm moist 

 weather, the common house fly may often be seen 

 in a dead or dying condition, sticking to a window- 

 pane, its abdomen distended and presenting alter- 

 nate black and white bands, while around the fly 

 at a little distance is a white powdery ring, or halo. 

 The white intersegmental bands are made by threads 

 of the fungus just named, and the white halo by 

 countless asexual spores known as conidia, which 

 have been forcibly discharged from the swollen 

 threads that bore them (Fig. 255) by pressure, result- 

 ing probably from the absorption of moisture . These 

 spores, ejected in all directions, may infect another 

 fly upon contact and produce a growth of fungus 

 threads, or hyphcz, in its body. The fungus may be propagated also 

 by means of resting spores, as found by Thaxter, our authority on the 

 fungi of insects. 



Empusa aphidis is very common on plant lice and is an important 

 check upon their multiplication. Aphids killed by this fungus are 

 found clinging to their food plant, with the body swollen and discolored. 

 Empusa grylli attacks crickets, grasshoppers, caterpillars and other 



PIG. 254. Fruc- 

 tifying sprouts of 

 a fungus, Cordyceps 

 ravenelii, a r i s ifn g 

 from the body of a 

 white grub, Lachno- 

 sterna. Slightly 

 reduce d. A f t e r 

 RILEY. 



