56 



INSECT ENEMIES OF THE BOLL WEEYIL. 



this is true whether we consider the involucral or fohar glands." The 

 parasites probably frequent the nectaries during the morning sunhght 

 hours and then are equipped to go about their other duties during the 

 hottest part of the day. 



In addition to these actual observations as to the preference of 

 parasites there are other very strong proofs of heliotropism. It has 

 been found that there is a decided increase in the parasitism of weevil 

 stages in hanging forms exposed to the sun over those in fallen forms 

 which are more or less shaded. It is also apparent that the faUen 

 forms most exposed to the sun receive the greater amount of para- 

 sitism. Among the hymenopterous parasites there is only one at 

 present which seems to prefer a moist shady place for its work. 

 This is Tetrasticlius liuntein Crawford, which is an internal parasite. 



A numerical study of the records of rearing of parasites from the 

 boll weevil shows that in the majority of the species the males are 

 relatively fewer than the females. The following table wiU show the 

 percentage of each sex and also the number of parasites upon which 

 these percentages are based. 



Table XIX. — Relative percentages of the sexes of boll-weevil parasites. 



Species. 



Total in- 

 dividuals. 



Percentage of sexes. 



Female. Male, 



Microbracon melUtor 



Catolaccus huntcri 



Catolaccus incertus 



Habrocyius piercei 



Cerambi/cobius cushmani 



Cerambycohius cyaniceps. . . , 



Cerambycobius sp 



Ennyomma gJobosa 



Eurytoma tylodermatis 



Eurytoma sp 



Lariophagus teianus 



Microdon to m ems anthonomi 



MyiopJiasia senea 



Sigalphus curculionis 



Tetrastichus hu nteri 



429 



30 



64 



509 



1 



8 



433 



2 



2 



223 



2 



13 



41 



Per cent. 



60.78 

 78.37 

 81.12 



100.00 

 71.88 

 70.34 

 

 37.50 

 64.90 

 50.00 

 50.00 

 84.76 

 50.00 

 61.54 



100.00 



Per cent. 

 39.22 

 21.63 



18.88 



28.12 

 29.66 

 100.00 

 62.50 

 35.10 

 50.00 

 50.00 

 15.24 

 50.00 

 38.46. 



OVrPOSITION. 



It has been found by numerical study of the large number of para- 

 sites collected during the last five 3'ears that whenever the parasitism 

 in a field reaches between 50 and 70 per cent there is a strong likeh- 

 hood of reduplication, with resulting superparasitism. The exact 

 records of superparasitism obtained in this investigation have been 

 published in another article (Pierce, 1910). Parasites have no power 

 of discerning the presence of another egg on the prospective hosts, 

 and hence there occurs at times a tremendous duplication of energies. 



