15 



Such forms of variation have also "been observed in the 

 case of Bacterium pieris liquefaciens alpha . 



Paillot theorizes that these "growth forms" probably 

 represent a degenerate stage of the "bacteria. The in- 

 creased ability of the organisms to give rise to these 

 forms corresponded to a diminution in their original 

 cirulence for the insects. This hypothesis is similar to 

 that which, according to some workers, characterizes the 

 symbiotes of aphids. In the absence of detailed work in 

 this field, one wonders what types of variation might 

 occur by the passage through insects of some of the "better 

 known "bacteria not usually found in association with in- 

 sects. One indication of such interesting possibilities 

 is that afforded by the work of Lai, Ghosal, and Mukherji 

 (1939) who found that certain morphologic, metabolic and 

 chemical changes occurred in strains of Vibrio comma 

 passed through house flies ( Musca domestica) . 



Involution forms occurring on artificial media frequently 

 arise in cultures of bacteria isolated from insects. 

 Bacillus liparis is normally a slightly elongated, straight, 

 or slightly bent rod, but when cultivated on carbohydrate 

 media such as levulose agar, huge forms, swollen in clubs 

 at one or both of their extremities, may be observed. 

 These forms resemble very closely certain involution forms 

 of the diphtheria bacillus. 



Bacterium neurotomae , isolated from Neurotoma ne moral is , 

 appears in the blood of various insects in the form of 

 elongated but rarely filamentous rods. However, in young 

 cultures on agar some of the cells swell greatly and 

 become more or less rounded. In the central part of these 

 rounded cells is consolidated the chromatophilic substance 

 and the whole aspect is one of true nucleated cells. 

 According to Paillot, however, they are without vitality 

 and rapidly degenerate. 



From the lyreman cicada, Tibicen linnei , Steinhaus 

 (19^-1) isolated a gram-positive bacterium ( Bacterium 

 mutabile) which normally has the form of a short rod. In 

 fluid media, such as tryptophane broth, bizarre, slightly 

 branched forms appear. 



The Role of Bacteria in the Nutrition of Insects 



Inasmuch as most insects harbor large numbers of 

 bacteria within their digestive tracts, it is apparent 

 that these microorganisms may exert a profound effect 



