HOW INSECT CONTROL FOLLOWS WEEVIL. 35. 



Following the cold of November, 1908, the winter was unusually 

 warm, being at least 5° F. above the normal in both Louisiana and 

 Texas. From March 15 to July 15, in both States, the temperature 

 was almost normal. However, by this time there was an accumulated 

 deficiency of precipitation in each State of several inches. The 

 months of July and August in Texas were extremely warm and many 

 places recorded the maximum temperatures for their entire period 

 of records. While the heat was less excessive in Louisiana, it never-' 

 theless reached very high points. This extreme weather during these 

 two months had a tremendous effect upon the boll weevil and upon 

 its parasites, although records taken after some of the hottest days 

 showed that the mortality of the boll weevil from the heat was con- 

 siderably higher than the mortality of the parasites of the boll weevil. 

 After the middle of August a period of renewed growth of the cotton 

 plant gave the boll weevil an opportunity for increased development 

 and consequently permitted a large number of weevils to mature 

 before the hibernation season. Incidentally with this fall brood of 

 weevils, we find that there was a very great increase in the parasites, 

 especially in Louisiana. The following two diagrams (figs. 4, 5) 

 illustrate the temperature of the years under consideration. 



8. HOW INSECT CONTROL FOLLOWS THE DISPERSION OF THE BOLL 



WEEVIL. 



From an economic standpoint it is very important to know what 

 kind of natural control of the boll weevil can be expected in newly 

 invaded country. Since 1904 it has been noticed that maximum 

 infestation is generally reached by August 1, and that simultaneously 

 an extensive dispersion of the boll weevil takes place. At this period 

 the boll weevils fly to fields many miles beyond the parasites. The 

 climatic conditions during the dispersion period are such as will not 

 seriously interfere with prolific breeding of the weevils in the newly 

 infested territory. The extent of the dispersion is limited only by 

 the number of weevils flying and the amount of food supply available. 

 In the fall of 1909 the sparse production of cotton in southern Missis- 

 sippi brought about a dispersion of 120 miles into new territory. | 



Our knowledge of the insects which attack the boll weevil shows 

 that most of them are derived from the parasites of similar weevils 

 that are native to the region infested. Therefore, if parasites and 

 predators are present in the invaded region, it is reasonable to expect 

 that they will immediately begin attacking the boll weevil. This 

 assumption has been proven in many definite cases. At Minden, La., 

 in 1906, a parasite larva was found in a green square infested by the 

 first generation. At Roxie, Miss., where the weevils had been present 

 only a few weeks in September, 1908, ant work and parasite work 



