376 K. M. SMITH 



(1950), and the differential staining properties of the polyhedra later investi- 

 gated (Smith et ah, 1953). Previously, several workers had observed polyhedra 

 in the cytoplasm of the mid-gut (Ishimori, 1934; Lotmar, 1941), but the fact 

 that they were of an entirely different nature from the nuclear polyhedra was 

 not realized. 



The reaction of the cytoplasmic polyhedra to stains and alkalies differs 

 sharply from that of the nuclear type and is an important aid in diagnosis. 

 In smears made from infected caterpillars, fixed by mild heating and 

 subsequently stained with methylene blue or Giemsa solution, the cytoplasmic 

 polyhedra take up the stain readily. This is in marked contrast to the 

 behavior of the nuclear polyhedra, which under these conditions do not stain 

 at all. Figure 7 shows a smear made from a larva of the privet hawk moth, 

 Sphinx ligustri, which had a double infection with both nuclear and cyto- 

 plasmic polyhedroses; note how the latter are clearly differentiated. 



a. Location of Cytoplasmic Polyhedra in Insect Tissues. The number of 

 cytoplasmic polyhedroses now recorded is extremely large and it seems highly 

 probable that they are more numerous than the nuclear diseases; this, at all 

 events, has been the writer's experience in his studies at Cambridge. In every 

 case the virus appears to develop in the gut cells, usually the mid- or hind- 

 gut, and in a late stage of the disease the cells become completely filled with 

 polyhedra. These also occur in the lumen of the gut and are excreted in large 

 numbers in the feces (Fig. 8). 



In a cytoplasmic polyhedrosis of the silkworm, Bombyx mori, the polyhedra 

 are produced in the cylindrical cells of the mid-gut epithelium but not in the 

 goblet or interstitial cells (Tsujita, 1955). In a similar disease of the spruce 

 bud worm, Choristoneura fumiferana Clem., the polyhedra occur in the cyto- 

 plasm of the digestive cells of the mid-gut epithelium (Bird and Whalen, 

 1954). 



The symptomatology of the cytoplasmic polyhedroses usually differs sharply 

 from that of the nuclear disease. The main difference arises from the fact that 

 the skin is not attacked and, in consequence, the larva, though limp and 

 flaccid, does not disintegrate in the manner so characteristic of nuclear 

 polyhedroses. In some species, the mid-gut is clearly differentiated through 

 the skin by the accumulation of the polyhedra in the cells. This may occur 

 quite early in the disease before the general health of the larva appears to be 

 affected and is most marked in the cytoplasmic polyhedrosis of certain 

 species, notably Phlogophora meticulosa, the large angleshades moth and 

 Diataraxia oleracea, the tomato moth (Fig. 9). 



b. Development of Cytoplasmic Polyhedra. Xeros (1957) has described the 

 formation of the polyhedra in a cytoplasmic disease of the larva of Thaumato- 

 poea pityocampa. Bodies which are apparently virogenic stromata appear in 

 the epithelial cells before the formation of the polyhedra. Later, small 



