THE PEA APHIS WITH RELATION TO FORAGE CROPS. 



51 



at any time except in fall or early winter, and climatic conditions no 

 doubt have some direct or indirect influence. 



In our experiments oviparous females were produced much oftener 

 than males, probably accountable from the fact that individual males 

 may fertilize several females. The oviparous females are invariably 

 wingless; but we have found both winged and wingless males, the 

 latter in only a few instances in 1911. In the field Mr. Hyslop also 

 observed the wingless male. In the case recorded by him a winged 

 and wingless male were attempting to mate with the same female. 

 To our knowledge these are the only two records of the occurrence 

 of wingless males in America. 



Mordwilko (10) has observed wingless males in Russia, and in his 

 writings has described this form. 



Copulation takes place soon after the individuals reach maturity, 

 and egg laying commences shortly thereafter. Eggs are laid on the 

 stems and leaves of red clover, according to our observations in 

 Indiana; but Mr. Hyslop, in his observations with this species on 

 alfalfa, mentioned above, found eggs only on the leaves of alfalfa 

 and in no case on the stems, petioles, or axils. We have no records 

 of the sexual forms being produced or eggs being laid on any plants 

 other than red clover and alfalfa. However, Mordwilko (10) has 

 observed the sexual forms on Medicago falcata, Laihyrus latifolius, 

 and L. angustifolius , and Theobald (11) found them on the flat pea 

 (Laihyrus sylvestris) . 



FECUNDITY OF OVIPAROUS FEMALES. 



Actual counts of the number of eggs laid by individuals were not 

 made, but dissections of 12 unfertilized females several weeks after 

 maturity showed that they were capable of laying an average of 25 

 eggs. (See Table VII.) These counts indicate that the fecundity 

 of oviparous females of pisi is twice that of the average aphidid. 



Table VII. — Number of eggs of Macrosiphum pisi. 



Date. 



Dec. 6,1912 



Do 



Dec. 10, 1912 



Do 



Do 



Do 



Do 



Do 



Do 



Do 



Jan. 4,1913 



Do 



Average. 



Number of eggs 

 laid previous to 

 date of dissec- 

 tion. 



1 or2 



1 or2 



Avg. of 2 per 2 . 



do 



do 



do 



do 



do 



do 



do 



Number of 

 apparently 

 fully devel- 

 oped eggs 

 found in 

 body. 



Number of 

 immature 



eggs in 



body. 



Total num- 

 ber of eggs 

 exclusive 

 of undevel- 

 oped ones. 



27 

 24 

 18 

 25 

 25 

 19 

 18 

 25 

 21 

 17 

 26 

 30 



2+ 



Several 



28 or 29 



25 or 26 



20 



27 

 27 

 21 

 20 

 27 

 23 

 19 

 28 

 32 























23 





24.8+ 





