THE MEXICAN BEAN BEETLE 3 



high moisture environment beneficial. Eddy and Clarke (1929) note that 

 warm, moist weather favors spring emergence from hibernation. Thomas 

 (1924) in Alabama emphasized the importance of high moisture for hiberna- 

 tion and a temperature l)etween 65° and 91° F. and relative humidity between 

 40 and 95 per cent for egg production. His records were not secured under 

 controlled conditions. Pejiper (1926) noted the destruction of inmiature 

 stages in South Carolina during a heat wave. Marcovitch (1926) found that 

 drouth destroyed the insect in Tennessee and was a more important limiting 

 factor than cold. He considered the himiid conditions of the East favorable 

 to the pest. Douglas (1928) foimd that temperature alone would not cause 

 emergence of tlie adults from hibernation quarters, but that moisture was 

 es.sential and more important than temperature. Cecil (1928) stated that the 

 beetle would successfully survive the winter temperatures prevailing in New 

 York State. The writer (1929) demonstrated the necessity of humid condi- 

 tions for the bean beetle to maintain itself in abundance, and showed that its 

 distribution in the West, as well as the East, depended upon that factor. 



All of the above conclusions are based upon outdoor observations where 

 several possible factors maj'^ have been important in producing the results 

 mentioned. A considerable diiference of opinion between the various workers 

 is evident, and some of the citations are decidedly misleading and contrary 

 to fact, as will be brought out later. Accurate data of the physical factors 

 affecting the immature stages are especially lacking. 



Description of Stages and Injury 



All stages, — eggs, larvae, pupae, and adults, — of the bean beetle are con- 

 spicuous in the field. 



The eggs are pale or orange yellow in color, nearly elliptical in outline, and 

 about twice as long as wide. They are attached at one end and laid irregu- 

 larly in groups of about fifty on the under sides of the leaves. 



The larvae have four instars, molting three times previous to the jDupation 

 molt. The newly hatched larvae are about 1.5 mm. long, pale greenish-yellow 

 in color, with their bodies armed with spines. The developing and mature 

 larvae are yellow, with six rows of spines which become strongly branched and 

 black at the tips (Plate I, B). When over half grown they appear to be 

 "humped", the longest spines and thickest portion of the body being in the 

 middle. The abdomen in all instars tapers to the anal segment which is pro- 

 duced to form a sucker-like apparatus by which the larvae are aided in cling- 

 ing to the leaf, and by which they fasten themselves previous to molting. 



The pupae are light yellow in color, spineless, and about the size of the 

 adults. They hang head downward from the under surfaces of the leaves and 

 are partly covered and protected by the shed larval skins, which are attached 

 by the posterior end to the surface on which they are fastened. 



The adults are robust, hemi-ovoid beetles with rather slender legs, and are 

 about one-fourth of an inch in length and one-fifth of an inch wide. When 

 newly emerged the color is yellow, gradually darkening with age to bronze or 

 brownish. Each wing cover is usually marked with eight small black spots 

 (Plate I, B). 



Both the adult and larval stages are destructive (Plate I, B). The beetles 

 cut irregular holes through the leaves, leaving portions of tissue and the 

 larger veins. The larvae are voracious feeders, and do more harm than the 



