8 MISCELLANEOUS STUDIES 



of short tubular processes, the cornicles (honey tubes, nectaries of 

 some authors). These are quite valuable characters, both specific and 

 generic. In the Phylloxerinae and most of the Pemphiginae they are 

 lacking, but in the Aphidinae they are always present, and show a 

 great diversity of form. They may be merely pores (certain Callip- 

 terini, Cerosipha cupressi Swain, Lachnus taxifolia Swain), they may 

 be cylindrical, yet quite short (certain Callipterini, Chaitophorini) ; 

 they may be short and cylindrical or conical (Aphidini) ; they may 

 be truncate, cone-shape (Lachnini) ; they may be clavate and long 

 (certain Callipterina, Pterocommini, Macrosiphini) ; or they may be 

 long and cylindrical (particularly in Macrosiphum and Myzus). 



BIOLOGY 



Considerable variety is exhibited in the habits, life history, and 

 methods of reproduction, as well as in the structure and body form. 

 Reproduction is almost entirely parthenogenetic, although certain 

 species at certain times have a sexual reproduction. Fewer species 

 have sexual reproduction in California than in colder climates, due 

 to the fact that mild weather throughout the winter permits them to 

 live over, and hence the eggs are unnecessary. Many species produce 

 generation after generation parthenogenetically, and are most abun- 

 dant in the spring and early summer, but gradually disappear toward 

 midsummer, due partially to their predaceous and parasitic enemies, 

 and partially, undoubtedly, to the heat of the summer. Other species 

 regularly produce sexual forms in the fall, which lay eggs that hatch 

 the next spring. The forms hatching from the eggs are wingless 

 (except in Callipterini) and usually of a different form from the 

 later generations, and are known as the fundatfix or stem mother. 

 The fundatrix is always viviparous. Her progeny consists either of 

 all apterous or partly apterous and partly alate viviparous females 

 (fundatrigenia), which in turn produce other generations of funda- 

 trigeniae. The last asexual generation in the fall, which gives birth 

 to the sexual forms (sexuales), are known as sexupara, and are usually 

 alate. Oftentimes in the second or third and even fourth generation 

 there is a definite migration from one species of host plant to another, 

 where the aphids live over the summer (virgogenia), the sexupara 

 returning to the original species of host in the fall to give birth to 

 the sexuales, which lay their eggs there. Aphis malifoliue Fitch rep- 

 resents an example of this habit, the winter host being apple, the 

 summer plantain. Oftentimes the fall migrants (sexupara) of certain 



