32 BULLETIN" 66, UNITED STATES NATIONAL MUSEUM. 



b. Head. — In Andrena trimmerana the head of the stylopized 

 individuals is usually smaller than that of normal individuals. This 

 condition is due to the turning of the nutritive elements to the 

 abdomen where they are needed by the parasite (Perez, 1886), 



c. Color. — Dr. W. M. Wheeler has found that parasitized Polistes 

 metricus are much altered in coloration and has in preparation a 

 series of notes on these color changes. Prosopis gibba occasionally 

 exhibits irregular rufous patches on the abdomens of affected in- 

 dividuals (Saunders, 1850). Prosopis rubicola exhibits color change 

 regularly. "The nymphs of those Hylaei which are likely to pro- 

 duce the pale-colored specimens (H. versicolor), which prove, as 

 anticipated, to be only a variety of the H. rubicola consequent upon 

 parasitic absorption, may usually be identified within one or two 

 days of their final metamorphosis by assuming a yellow tinge, and 

 may be set apart as certain to produce male parasites" (Saunders, 

 1852). 



d. Villosity. — According to Perez the villosity of the abdomen of a 

 stylopized Andrena is much more dense, especially on the last seg- 

 ments and its coloration is altered. In general the stylopized bee 

 has the hairs of the last segments, more abundant, longer, more 

 silky, both on the marginal fringes and the disk of the segments, and 

 the color becomes lighter reddish or golden. As examples Perez 

 (1886) ites Andrena piceicomis (stylopized) isolita Dufour, and 

 A. labialis (stylopized) separata Smith. Note Mr. Crawford's ob- 

 servations on Andrena crawfordi beyond (p. 34). 



The villosity of the thorax in species having scaly, short, ap- 

 pressed hairs covering the tegument may be altered by the elon- 

 gation and redressing of the scaly hairs and giving them more of the 

 appearance of ordinary hairs. As example Perez cites Andrena 

 aeneiventris Moraw. 



e. Punctuation. — The punctuation becomes finer, more super- 

 ficial and closer, as for instance Andrena trimmerana Kirby, Andrena 

 fulvescens Smith. Note the contrary observation by Mr. Crawford 

 on Andrena crawfordi (p. 34). 



5. Alteration of external sexual characters. 



Secondary sexual characters. — a. Color of clypeus. — In the genus 

 Andrena the color of the clypeus in many species is used to distin- 

 guish the two sexes, the males having a yellow or white clypeus 

 while the females have the same black. It was found by Perez 

 (1886) that when these species are parasitized the color of the 

 clypeus tends toward the normal coloration in the opposite sex. To 

 exemplify this point he cites the following species: A. {variabilis) 

 flmbriata Brulle, A. leucolippa Perez, and A. labialis Kirby. Certain 



