318 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 1 



acteristic would tend to increase the chances of the host species. The 

 phenomenon of retarded development is often observed also in para- 

 site species. Entomologists may take advantage of this factor by re- 

 frigeration of immature parasites until they are needed for work, 



5. Possible parasites per Jiost. A host may support one or many 

 parasite individuals at a time. When a parasite places a single egg 

 in a very young host and that egg subdivides as the host grows, some- 

 times forming a sufficient number of parasites to entirely consume 

 the host, the case is designated as polyembryony. This property is 

 suspected as occurring in Tetrastichus on Orthoris crotcJm Lee, and 

 in several species of Horismenus which attack bruchids and Lixus. 



The boll weevil is seldom capable of furnishing food for more than 

 one parasite, although sometimes two are bred. On the other hand 

 none of the boll weevil parasites are able to recognize the existence 

 of another parasite egg or larva upon a prospective host. In fields 

 where the percentage of parasitism has reached a very high point, 

 such evidences of duplication are very numerous. In one instance 

 thirteen eggs of a single species were found on one larva, although 

 only one could possibly mature, cannibalism settling the fate of the 

 rest. 



A very striking example is presented by Pediculoides. If a single 

 mite finds a weevil larva, two generations of its offspring can be bred 

 on the original host ; in the case of wasp larvae, even more generations 

 may be reared. 



6. Proportion of sexes. In computing the possible gains of parasite 

 over host, a very important consideration is the proportion of sexes 

 in the two species. The most striking phenomenon in sexual relation- 

 ships is of course parthenogenesis, which is supposed to occur with 

 many parasite species, and among hosts is most prominent in the 

 aphids. 



In Pediculoides males and females born ovoviviparously from the 

 same parent, mate upon the body of the parent, after which the males 

 die. 



Large series of examinations in the boll weevil problem have shown 

 the following percentages of males : the host, Anthonofnus grandis, has 

 58 per cent of males, Bracon mellitor Say 39 per cent, Catolaccus 

 hunteri Cwfd. 22.8 per cent, Cerambycohius cyaniceps Ashm. 26.7 

 per cent, Enrytoma tylodermatis Ashm. 35.4 per cent, Microdonto- 

 merus anthonomi Cwfd. 15.3 per cent. The last named species has 

 shown the most remarkable gains, 



7. Condition of Itost. Wlien the parasite species requires a certain 

 stage of the host for attack, its activity is sharply limited. This lim- 



