ECOLOGICAL STUDIES OF THE MEXICAN BEAN BEETLE 



By Harvey L. Sweetman' and H. T. Fernald, 

 Professor of Entomology 



The Mexican bean beetle, EpUachna corrupta Muls., is a native of south- 

 western North America. It has been a pest of beans in southwestern United 

 States since about the middle of the last century. The beetle has spread over 

 most of the East since 1921 and has been very injurious to the bean crop 

 through most of its ran^e. It was found in New England in 1929 in Connecti- 

 cut and Massachusetts, having apparently spread from New York State. The 

 insect is capable of becoming a very serious pest of the bean crop in New 

 England if the environmental conditions prove to be favorable to its repro- 

 duction and spread. The data presented here are the results of a study of 

 the influence of the physical environment upon the bean beetle. 



Review of Ecological Literature 



The ecological factors affecting the bean beetle have received very little 

 attention from most workers. The discovery of the insect in Alabama in 1920 

 caused much speculation regarding the effects of climate on it. 



Hinds (1920) stated that there were not any climatic or geographical bar- 

 riers to prevent the pest from spreading, but later (1922) attributed the slow 

 dispersal southward in Alabama to the prevailing winds. Montgomery (1920) 

 thought that losses from the bean beetle were not great in the Southwest 

 because of climatic and other conditions. This thought is somewhat mis- 

 leading as serious injury is rather common in that territory. Howard (1922a) 

 considered a temperature of 100° F. or over in dry weather to be very de- 

 structive, and found (1922b) that the larvae were killed in a few minutes 

 when in direct sunlight if the temperature was above 90° F. Later (1924) 

 death of the larvae was noted as occurring during heavy rains, but drouth 

 was not thought to be injurious as long as the plants were green. Howard 

 and English (1924) witnessed large numbers of the immature stages being 

 destroyed during a hot, dry period, but this was due partially to lack of food 

 and to exposure to direct sunlight. They foimd also that moist places were 

 essential for successful hibernation and that the beetles migrated if the hiber- 

 nating quarters became too dry. Howard (1922b, 1924) had emphasized the 

 fact that the adults required moist, but well drained, places for successful 

 overwintering. Later Howard (1927) in collaboration with Transeau (1927) 

 found that the regions in which damage occurred in Ohio coincided with areas 

 that were originally mixed mesophytic forest. The previous year De Long 

 (1926) in Ohio had stated, "There is an ecological factor that is controlling 

 very decidedly the distribution." Graf (1925) from a climatological study 

 concluded that temperature and moisture were not important factors in limib- 

 ing the distribution of the pest. Later (1928) he stated that low winter 

 temperature alone could not be depended upon to control the pest. Eddy 

 (1926) and Eddy and McAlister (1927) in South Carolina consider low hu- 

 midity and high temperature very detrimental to the immature stages, and a 



■' Candidate for a graduate degree in Entomology. 



