227 



markings begin to appear; Aving-pads larger and blackish; antennae 6- or 7-jointed, 

 the last three joints being black. 



Fourth larval stage : duration about four days. Length of larva 0.038 inch ; black 

 markings usually quite distinct; Aving-pads still larger; antennju 8-jointed. 



Fifth stage : duration five or six days. This proved to be the pupa state, and the 

 pupa differs from the preceding larval stage only in the more intense and more 

 numerous markings on the thorax. 



Not the least interesting point in Mr. Slingerland's account is the 

 discovery that Psylla pyricola offers a very marked example of seasonal 

 dimorphism. That hibernating imagos of Psyllid* usually differ from 

 the summer generation in the more intense coloration of the body, and 

 sometimes also of the wings, has long been known, and the explanation 

 given for this difference is that Psyllid^e acquire their full coloration 

 very slowly and that the older they become the more pronounced and 

 darker are the markings. The short-lived summer generation or gen- 

 erations are thus, as a rule, lighter-colored than the 

 long-lived winter generation, and the latter grad- 

 ually acquires the more intense color. This is well 

 exemplified in our common Trioza tripunctata Fitch 

 and Aplialar acaWuc L., which have at least two ^^G-P^Psyiiapyricoia: 

 annual generations,* but in these instances there siingeriand). 

 is no sharp delineation between the summer and 

 winter forms. Now, Mr. Siingeriand establishes the fact that in the 

 winter generation of Fs. pyricola there is no such gradual change in 

 coloration, but that in the fall of the year there issues from the 

 nymphs a hibernating generation of imagos which are at once uniformly 

 different from the imagos of the summer generations. Mr. Siingeriand 

 says: 



The hibernating adults differ from the summer adults in size, being nearly one- 

 third larger ; in their much darkei coloring, the crimson becoming a dark reddish 

 brown ; and especially in the coloration of the front wings. The summer forms or 

 typical pyricola have the veins, even in darker specimens, of a light yellowish brown 

 color, and the whole front wing has a slight yellowish tinge. The veins of the 

 wings of the hibernating adult are invariably of a dark brown or black color; the 

 front wings are quite transparent, with more or less blackish shades in the cells and 

 a blackish shade in the basal cell along the whole suture of the clavus. The male 

 genitalia differ slightly in size in the two forms. 



This winter form has been identified as the Ps. simulans Forster, 

 which by European authors has always been considered as specifically 

 distinct from Fs. pyricola. 



The discovery of this seasonal dimorphism is certainly a matter of 

 great interest, but that the last word has not yet been said on the sub- 

 ject would appear from the fact (overlooked by Mr. Siingeriand) that 



* Other hibernating Psyllidse, which, in all probability, have two or more annual 

 generations, e. g., our common grass Psyllids, Livia vernaUs and L. maculipennis 

 Fitch, do not differ appreciably from the summer forms. All specimens of the genus 

 Pachypsylla fouud in early spring are darker or more sordid than those found late in 

 the fall, but in this genus there is no summer generation of imagos. 



