RETREAT OF L. JUNCTA. 49 



DlSTiUBUTION OF Iv. DEFBCTA AND L,. JUNCTA AND RETREAT OF Iv. JUNCTA. 



Leptinotarsa juncta Guer. and L. dejecta Stal are two closely related species 

 with a peculiar distribution. L. dejecta is known from Texas, Arkansas, 

 and Missouri, and Stal has described it from Yucatan. As far as I am able 

 to learn, neither juncta nor defccta occurs in Mexico or Central America, and 

 as careful search along the coast belt of Mexico has failed to reveal any 

 traces of these beetles, I strongly suspect that Stal's record from Yucatan is 

 incorrect. 



L. juncta had originally a much wider range than at present. In 1865 it 

 w is found throughout the Atlantic Coastal Plain from Maryland south to 

 the Gulf of Mexico, over the entire Piedmont belt, along the Gulf coast into 

 eastern Texas, and up the Mississippi Valley to southern Illinois. It appar- 

 ently entered the Allegheny Plateau along several river systems, especially 

 the Coosa-Alabama or Allegheny River. Westward it spread into southern 

 Missouri, Kansas, Arkansas, and Texas. Over this entire area it was a 

 common form feeding upon Solatium caroliniense (plate 10). 



But with the advent of L. decemlineata into the eastern United States Juncta 

 very soon retreated or was exterminated. Evidently the two are unable to 

 live in the same habitat, for, although they have different food plants, Juncta 

 disappears in any locality soon after the arrival of decemlineata. For example, 

 it was formerly abundant about Washington, District of Columbia, and in 

 parts of Maryland, but Dr. Howard states that since the advent of decem- 

 litieata into that region juncta has retreated southward, and the same is true 

 in southern Illinois, where it is no longer found. Professor Ouaintance 

 informs me that in 1899 an d previously juncta was perhaps the most common 

 insect about the station grounds at Experiment, Georgia, but that in 1900 

 it was found in only very small numbers, its place having been taken by 

 decemlineata ; nor is it longer found in Virginia, the Carolinas, Kansas, 

 Missouri, and the upper Mississippi Valley. 



Why juncta should retreat before decemlineata is a question of considerable 

 interest, as the two species have entirely different food plants, and it can hot 

 be thaX. juncta is crowded out by the larger numbers of decemlineata. I am 

 informed by Professor Quaintance that the two species hybridize freely in 

 nature, although the eggs that are laid are not fertile, at least in so far as his 

 observations go. Concerning this crossing in nature and its effect upon 

 juncta I shall have more to say in a later paper. The full explanation of 

 the extinction of juncta is to be found in the fact that the two species cross 

 freely in nature, and that this natural crossing has resulted in a most inter- 

 esting and peculiar case of prepotency in one species and of submergence in 

 the other. 



